Although these are guides, the author does not advise anyone to actually build nor even consider building such devices. Read, but do not act upon this information because dogs of law lie around every corner, so everyone should live a quiet, pastoral life. This is because the author simply does not want some parasitic lawyer coming on heavy because some damn fool thinks they are some brilliant engineer, or stubbed their toe and wants a fortune because they happen to be stupid. I gladly put my knowledge on the web to help make a better world, not so that some damn fool can sue me. As lawyers get richer, the rest of society gets poorer. A wise man once said, that a society needing few doctors and lawyers is a healthy society. Britain and the USA are awash with doctors and lawyers.
Do not read nor act upon the information on this website.
Always vote to keep all lawyers and assholes out of politics.

If you're a kid hanging around British streets with nothing to do, then don't expect grown ups or politicians or the social services to help you develop your life into something worthwhile.
Just make your own life better through simple steps. Look for a friends garage or back yard, search out some metal and a good metal supplier and ask around for an unwanted motorcycle engine or a whole bike. Even just a tarpaulin or groundsheet in the back corner of a garden and a couple of paving slabs can be enough to build your own custom machines. Then ask around for a welder and build up a small set of tools. It costs a lot less than a packet of cigarettes or a few cans of brew. You may wish to check out my motorcycle mechanics monograph.
Yesterday, I cycled 15 miles across Plymouth to buy some aramid (Kevlar tm) and 20 feet of 3/4 inch thin wall steel tubing for my latest project. The tubing cost 8 quid and I had to save up for a month, but it was a very nice afternoons ride. I carried a hacksaw to cut up the tube and bungeed it all along the upper frame tube.
If things work out well and your workspace has an unwanted garden shed, then you can even build your own wind tunnel. See website.
Most kids just stick pictures of bikes on their bedroom walls. By the time you are ready to take your motorcycle test, you and your friends may have built a few custom motorcycles and all for mere pennies.
If you like biking in Plymouth, then also check out my guide to Dartmoor Access routes.

Preface.

The modern rider still suffers ergonomics no longer acceptable for most people. When accompanied with poor weather protection and atrocious luggage capability, it can be seen that the evolution of the motorcycle has far to go.

This monograph is available for assessment only, an interim tome to run alongside the other web pages, including the trike, and welding and enclosed bike pages. Much of my design work is commercially sensitive and less than half way through the work, hopefully to appear in about ten to fifteen years if support is sufficient. I have three extremely radical motorcycle designs partially finished, awaiting support and funding to become road legal.

This monograph is just the steel and metal stuff.
The following is based on decaded of knowledge gleaned from an engineering apprenticeship, being a licensed Engineer, draughtsman, a degree in technology, science, computing, innovation and design, then a fewe years as a motorcyel mechanic, but more importantly building bikes for decades. Plus lots of other stuff, club motorcycle trials, riding Ducatis at Silverstone and long distance bike awards.
I have written this for the web, as I have now moved on to composites, where the JP8b/c series will hopefully be road legal if I can get funding, otherwise the ridable test rigs will simply collect dust in the back yard.

Meanwhile here is a guide to designing and building motorcycles, based on first hand experience of building far too many bikes to count, from mini motos (before the term was known back in '72), to advanced composite designs today. I hop eI have included just about everything in between, from simple frame mods to building your own engines, including writings in some national custom bike magazines, building award winning chops, recumbent HPV's, enclosed V4 tourers and V12efi trikes.

This monographs should hopefully help others get on with catching me up, and perhaps passing me :)

(If you are plagiarising parts of this for a project, then stop. Many students now get top qualifications for very little work. A modern British degree is now worthless. I know, - I've two and they are a complete waste of time. The jobcentre have even told me to leave both my degrees off my CV.
I know of a physicist who now works as a school cleaner, even though a superb scientist, she openly admits she is not very good as a cleaner. Still, it's a job of sorts and all that can be expected in our modern Britain.
Under Thatcher and now, 'New' Labour, many British universities now accept that our degrees are worthless.
I too must survive the appalling mess called Britain that I was once proud of. Britain should not be all about freemasons running banks and call centres owned by foreigners, but become worlds leader in science and engineering again. Please help make a better Britain and give unemployed British scientists and engineers a job. )

Gizzajob, please.
Please consider this monograph a minor C.V.

Introduction.

This first part is about getting your mind set to open and become free from conventional design. you may indeed return to making another clone custom bike, but at least you will have explored al the possibilities, and therefore your design will be both fuller in scope, and greater in potential. And hopefully a few readers will make giant leaps in motorcycle design, then build them to prove they work. I have done this many times and have always enjoyed the process and the riding.

This monograph uses commonly available technology applicable on a daily basis, for those who wish to learn from a hands-on approach. This mainly empirical approach has the intention of making construction more accessible for all and of maximum effort with minimum equipment.
The work here is aimed mainly at general motorcycle design in metal. Because this monograph is aimed at beginners, without professional levels of testing prior to use, this work takes a more basic, pragmatic approach to design, construction, safety and testing.
Building motorcycles has advantages and disadvantages. Be aware of both and consider your reasons carefully. Custom motorcycles are built by those who are not too happy with what is available today and need to modify or even totally rebuild a machine, possibly designing from the ground up. This is quite possible on a sensible, small budget, using affordable tools and materials available at the time of writing.

Because 'burEUcraps' like to legislate against people doing things on their own initiative, never vote for lawyers or others who aim to stem human aspirations or freedoms. Big bureaucracies always restrict far more than small government structures. The EU mega-monster paperwork is killing design and innovation, even bananas have to be straight. So never vote for anyone unless the offer freedom of design and reduce all the legislation which accompanies oppressive democracies. There are political parties aiming to curb EU stupidity, and some who promise to do so. I recommend you vote for a genuine democracy if you want real freedom.

Hopefully this monograph offers a reasonable balance of encouragement is offered towards innovation, without detracting from the safety and technical problems. A purely technical description would be comparatively easy, but encouragement and guidance are also important requirements of learning, all too often left out of reference books. Therefore no apologies are given for the basic as well as the innovative, wider approach to building such machines and devices. Use your skills AND your imagination !

Attention is drawn to the fact that there are many reference works explaining the technical and theoretical application of building motorcycles. In particular the readers attention is drawn to the work of Phil Irving and Tony Foale. In Phil Irving's classic book on the subject, 'Motorcycle Engineering', the design considerations of the construction of motorcycles is dated, but very well illustrated. Tony Foale's website discusses the geometry and handling, with some innovative work to liven up the subject.
I could not find a decent book or website regarding design and manufacturing your own machines, so I have written this.
If there is anything amiss, or missing, please email so I can update or improve the monograph. If I get no replies after a year, my monographs are dumped to make way for other works. It is for this reason that the trike monograph is gradually getting larger as I have quite a lot of feedback, and so I know someone out there is reading this, and I feel confident that my time is not being wasted.

Whether books or internet, there seems however, a massive gap between theory and practice.

Here is both theory and practice.

Don't worry, the theory is basic and there is no maths, so even Blairs generation of school kids should be able to follow it. (Don't blame the kids, blame New Labour.)

The theory of design and construction also needs explanation, especially the basics required for developing and refining a design from the ground up.
It is hoped this monograph will help towards bridging the many gaps, and become a starting point for even better machines in the future. This monograph aims at creating a path leading towards designing and building a new machine, then making sure it is safe to ride. In this manner, Britain may once again become the world leader in advanced motorcycle design.

This guide is not a 'stick part A to part B' type of guide, neither is it a 'how I built a bike' guide. It is exactly what it's called. - A guide concerning the design and building of motorcycles.

There are no drawings, despite many excellent drawings, photographs and computer 3D graphics available from the many off road, chops and custom bikes and the JP7 and Longbow programmes. This is an unusual decision, especially in a book which includes the design process, but seen as fundamentally important. If drawings are given, the reader may tend to naturally follow by example. But by describing in words, the reader has the advice and direction needed, but also the freedom from being channelled into a narrow mind set often caused by set-piece drawings.
Use your imagination.
The reader is recommended and encouraged to create drawings using their own initiative and to this end, is taken through the processes to build upon and refine their own designs.
It is important that drawings are done throughout the process. From initial designs sketched on A4, through full size working drawings on inexpensive lining paper, right down to the smaller details of the smallest brackets and lugs.

From the greatest architecture to nanotechnolgy, the pencil usually goes first, with simple sketches leading the way to whatever can be imagined. Many of the worlds best designs have been roughly designed on back of a napkin, especially if that is all there is to hand when a good idea surfaces.

Without specific drawings in this monograph, the reader will visualise much more of their dream and to encourage the aspirations, develop true, independent innovation and to minimise the all too common 'sheep' approach to design. This work could be swamped with drawings, but even the simplest detail drawing will naturally constrain the design process which should always be highly individualistic. Many excellent drawings are available world-wide, but simply copying without understanding where you are going is not going to advance machines. Far too many bikes are simply clones, often called customs, but rarely with any real imagination. The millions of custom chops I have seen, and help build a few show winners, are all essentially boring or even dangerous from a design point of view.
Copying from others will simply help to create more of the same and should only be considered a starting point during the early years of learning about design.

I totally agree with her.
The same applies to building custom machines. Following all the drawings in the world simply leads the designer along a path already trodden.
With their own drawings, the reader will see their own dream in their mind and then begin it on paper in a way that can make it become reality.
By reading this monograph, the reader may well have decided to go beyond the fairly staid selection of machines available and to venture further. Design and innovation comes from the mind, not from books or drawings. Books such as this are merely guides to a higher process. This higher process is an art and no amount of copying will inspire the reader towards better things.

As the process of designing and building progresses, a machine will pass though the initial logical stages into the artistic refinements where the drawings will hopefully change from mere engineering to an artistic blossoming of creativity.
The following takes the somewhat blinkered view of motorcycle building as an art, rather than technology or science. No excuse is given for this approach for two reasons:
One. Not all hi tech is a matter of sitting down with a calculator and following specific rules. Calculations do not take into account the variables of hand building, nor does it encourage a pragmatic study of the technology.
Two. What is today's hi tech materials is tomorrow's everyday kit. Materials as just that: materials, nothing impossible, nothing hyped. Most of us have lost the art of flint knapping, yet quite happily use steel, plastics and modern adhesives. We all move on.

Never set standards low.
Racing technology is fine for some, but real people need to be able to build for the everyday, real world. Do not assume that you need a racing bike for road use nor that a lack of racing team resources will give a lesser machine.
Building from scratch will enhance the readers chance to compete at any level, albeit if only in spirit and design, if not manufacturing or computing.
Alec Issigonis did not set out to make a Monte Carlo winner, he set out to make the perfect small car.
If the reader sets out to make their perfect design, then the history books may often follow.

The intention is to build a bike design for a specific person, with total control over all aspects of design.
The reader may be surprised what can be done at home.
While designing and building, do not follow blindly, but always be open to inventing and developing independent styles and methods.
No one has all the right answers for the perfect machine nor how to build them.
Throughout history, everyone has the chance to rewrite the book on motorcycle design. Yet so few take the opportunity and this is but one attempt. The more that try, the greater the chance that the books will improve.
I know only of a few who have jumped over the fences constraining the sheep in the field of conventional bike design, ELF, Monotrak, Chrysler, Mead and Tomkinson, the Ecomobile and the Ner-a-car.

Despite the sophistication, of many professional teams, mostly common tools are used for home building and expensive equipment is not needed.
The few special tools are described, along with means to make them. No expensive tools are needed. The main tool is the brain, even the best race teams can't improve on that. The information in this monograph should enable a machine which is innovative and ideal for the purpose, and yet build it at home with very few special tools. This may seem an extravagant task, even more so without illustrations, but can be surprisingly simple. Good design is often simple. How many times have people said 'I could have thought of that'. Simple things come from complex thoughts. Simple things also encourage carelessness. Go carefully.

What this monograph cannot supply is the time and effort to build up the skills, or the time and patience to study both the theory and the art of design. When aiming high, failure will ensue. If failure occurs too often, decide if the standards set are too high, or reconsider if such work is a good idea, because much is expected to create stunning machines.
If only a few failures occur, please consider if you can push your design and skills still further.

Always realise that careful study of failure is an important part of the learning process and an excellent way of focusing on development. No one is likely to build their dream machine first time out, nor should it be expected. The reader will, however, have started on the path toward their ultimate machine. The longest walk starts with the first step. Many will be pleasantly surprised even with their first step, and where it leads.

If a keen biker, then designing and building a machine will repay enormously in the future. This will help to ensure an improved ride from an ergonomic and thus medical point of view, which in itself is priceless, but also offer refined comfort and handling to suit personal riding style, also a conversation starter and a machine to enjoy for many years as it develops.
If you suffer from skeletal or musculature problems, then consult your doctor and build your bike in accordance with medical advice. A cycling doctor built a recumbent bicycle and suffered no back problems afterwards.

This monograph is aimed at the builder who wishes to push beyond what is presently available.
Anyone can get a parts catalogue and simply tack on different components such as frames or swing arms to make a slightly different machine based on the same original design. This monograph expects the reader to throw away such constraints, along with the custom catalogue. Someone has to make the necessary giant steps into the future, it can be anyone. It is hoped that such innovation is the driving force for the reader.
The various processes are given, with a few asides to expand upon the subject. This keeps the process in a reasonably logical flow, while allowing options to be considered at the appropriate time and in a reasonable context.
Before anything is created, the designer will have decided the primary purpose and any other general concept and aims of the project. The designer should have done primary research, anything from a web search for artwork or photographs of promising machines or details, to a full study of the technology and materials involved.

It is assumed that no single design is taken as the best design.

Particularly fruitful studies should include ergonomics, rake and trail for fork designs and wheel sizes, wheelbases and weight distribution. Upon these foundations a vast range of good machines can evolve.

This monograph does not assume the reader has a scientific background. Many good machines have been created by hands-on artisans who would shy away from the mathematics and theory associated with engineering. Conversely, even the experts do not always push the boundaries forward, nor always get it right. The intention is to create a machine as good as the best, but without undue expense. A machine as good as professionals is often possible. An equally good machine is indeed possible - and occasionally, an impeccable machine is created.
There are no prizes for not trying.

Riding skills:
Be able to ride all bikes and then some. From mini motos, Pukka trials bikes up through Dartmoor streams, to racing Ducatis around Silverstone and long distance touring awards - whenever possible, try it all, (I do). But understanding balance and control harmony on two wheels needs much, much more: I enjoy skiing, ice figure skating and flying gliders, all of which helps to develop a refined appreciation of how machines should work in harmony with the human form. Then build and ride radical motorcycles around the fun parts of Dartmoor, Snowdonia, Bordeaux and such like to develop a closer appreciation of how machines work and should be refined for your own needs.

With most of these in place, or prepared to learn them on the way towards your ideal machine, then you can begin.

That's enough trying to get a feel about what and why, and encouragement to get the reader to realise that hi - tech is not always high - difficulty.
The aim of this work is not so much a scientific study of motorcycle, but a guide to help create a working and effective design.

The first section regards basic design.
Drawings.
The design process is a fundamental stage of any manufacture. It also automatically generates the working drawings. No highly competent drawing skills are assumed, nor expected.
If like many who managed to fail hand painting at play school, then make the drawings anyway, it's the ideas that are important.
Many people shy away from designing on paper, but even a rough sketch will save many hours of grief and effort later.

Sketching is merely a way of developing, then refining the thought processes and thereby reducing design conflicts. What is required is good, honest, applied technology on paper, not an oil painting. If you failed finger paining in primary school, don't worry, what is needed is ideas, not a work of art.
Some of the worlds finest designs started off as extremely rough sketches.

There are many ways to design a motorcycle. One way is to start with a favourite engine and build a machine around it, redesigning components, anything from mirrors right up to the complete frame and beyond.

From the point of view of many designers, one common method is that of styling exercises to which reality may be applied, hopefully to minimally compromise the overall effect. When designing a concept machine, always understand the fundamentals and try not to compromise the concept as it develops. Wherever applicable, use design to enhance and make the concept different or radical to advantage, so the overall concept can be refined towards a more perfect design. Only then should engineering be applied in a more specific manner to make the design road worthy. Some compromise will ensue as the machine is built and tested, but the following designs will often be much better if the fundamental concept is always in focus.

Alternatively for those who are actually serious about designing a motorcycle as a machine, it is recommended that the purpose is properly decided, free of any constraints. Such as simply a wish to tour in comfort, or to go very fast. In such a path, there are two routes, machine oriented or rider oriented.

It should be decided from the outset - if the machine to be for a specific purpose, with the rider merely as a control device such as for speed. Alternatively if the rider is the prime design component, as when commuting or touring, then the machine may be merely a device for transporting the rider in comfort, economically, or for easier traffic negotiation, or whatever is required.
It should be decided from the outset - Whatever is being designed, do not be happy until your sketches stands out from the paper. Then sweat blood to keep and enhance this style so it will stand out from the crowd when built. A few more weeks drawing radical designs can often change the whole path of a project.
Occasionally, the concept shouts at you from the page that it must be built.
You will know when this happens.

From this can be decided the fastest, optimum or most comfortable speed for the engine, possibly the average economical touring or a racing speed, from which a general engine power can be calculated, according to intended load and expected aerodynamics.
Compare with equivalent machines for sensible, 'ball park' figures.
It is assumed that a relaxed or efficient cruising speed and probably a top speed is required. From this a high spec sports engine, or a larger capacity touring engine can be chosen on the horsepower developed and the amount of aerodynamic efficiency such as something between a bare bike to one with a full fairing. This usually offers a handful of various engine forms and layouts, from which the design can be optimised.
finding bike and car engines is child's ply and usually cost pennies if you are prepared to repair them, such as a damaged outer casing, or an oil leak, or broken carb.
(As an ex bike mechanic, I keep a handful of various engines under the workbench, and can acquire a specialist engine if needed. I almost fitted a Ducati 998 EFI for 400 quid for the third and last prototype of the JP7 series, but the project died from lack of interest in Britain.)

A specific selection of engines can now be chosen depending upon preferred power and torque curves, physical size, reliability, spares availability etc. Only later will the final engine choice will be narrowed down to an ideal device as part of the design process.

Once the engine power, load and working speeds are decided, the tyres can then be chosen.
Tyres are extremely important, so always aim for an uncompromised size. Do not confuse uncompromised size with bigger is better, quite often the reverse.
Size often relates with power, not handling.
Some of the finest handling machines had narrower tyres than one would expect according to contemporary wisdom or 'expertise'. Common sense based upon personal riding experience is best. Then allow for a slightly larger tyre when designing, so a variety of choices can be used during final testing of types and profiles.

From the above, a moped, global tourer, record breaker or 24hr endurance racer can be developed.
Get the basics honed in early and the rest will follow in a sensible, safe and harmonious manner. From this the weight balance and all the other variables will, in most cases, naturally fall into place.

Understanding the components.

To start learning the skills, if no convenient motorcycle component is chosen as a simple starting point, then alternatively a test piece can be built to assess manufacturing and welding skills while also using the test piece to assess parts of the design, such as engine vibration damping. Make a component mimicking a major part of the design, but which can be broken with reasonable force, preferably at full scale.
It is very useful to make parts which can be assessed during design, to get hands on knowledge as early as possible in the design process.

With innovative design, all components should be considered independent of conventional design, but the few that are normally retained are engine mounts, some brackets and bearing housings and any head stock, where used.
A good test piece is a steering head as mentioned later. It demands sawing, careful filing with a set square, accurate alignment and the ability to work to very close tolerances.
Building a steering head from scratch is normally a lathe exercise, but can also be built by hand. It need not be a high quality machining exercise, but a hand skills test which should be able to offer a good steering head, built from just basic tubing and only by hand skills after the second attempt.
On a motorcycle in the twenty first century, the head stock should not necessarily be a design component with a natural or generic form. In the age of hubcentre steering, it may even be redundant.
The fundamental, essential design of a dual bearing tube and axle can also be used for wheel axles and swing arm pivots. The readers must come to their own conclusions as to which components can be made prior to design, with the intention of getting some feel of the materials. Learning to weld is mentioned later, but also fundamentally important from the outset. When you can build a good working steering head / swing arm pivot / axle, then the rest will not be too intimidating. See later - making your own steering head.

As the wheels and some other components need refined skills, do not consider building your own yet, but look for suitable commercial components.

As most people will be making a frame from scratch, it is worth getting to know the skills required. Engine mounts are also good test pieces, but this time as a test piece for understanding the art of engineering with powerful devices such as engines. This allows the engine to be supported by the test items in a simple wooden support frame to mimic the proposed frame, or perhaps just a couple of old wooden planks. This can then be subjected to loads with engine running with the intention of trying to break early endeavours from loading and vibration fractures. If making rubber engine mounts, then feedback and tuning of the pieces of rubber to the engine vibrations will be useful. This kind of approach should build up confidence in the materials and design in an area which will be subject to much load and stress, while getting to know the engine mounting, an important component with many needs and pitfalls. A simple engine mounting would be short versions of the lower two frame rails, or perhaps the wrap around frame, the engine brackets and a rear lug to fix the drive chain to test the clutch and basic forces. This can then be supported at front and rear to see how the engine behaves.
(My latest engine mounts are variable designs and made in composites, using the incredible strengths available, with almost no weight, yet adaptable to fitting many different engines in the JP8c series.)

When a swing arm and drive train is added to a simple wooden block or steel tube test rig, it can then be assessed under acceleration for the rise or squat properties of the swing arm pivot relative to the engine sprocket under load from a disk brake. A little carefully designed rise or squat of the rear suspension can be useful in a trials bike or road racer. See later.
Where cost is a problem, then the design of the bike frame and swing arm can be used as the test rig, before the front end or other items are added, and the basics tested until it works reliably and as intended. This will also ensure the engine works at the test riding site, - without the common hassle of many lesser customs which may look pretty but fail to run properly, or at all.

There is no better way to get used to building with steel than hands on. Then seeing just how little is needed to cause (safe) failure. Engine choice and mounting options are mentioned later.

When the materials are understood, then the integration of both the engine and rider can be considered fully. Most considerations will depend upon the engine, a component most designers will retain in a fairly standard form. The rider will be a known factor for a special machine, or built to standardised ergonomics when used by many riders. Before the more involved work can begin, the engine choice and any of it's modifications should be decided.

Road bikes.
Road bikes should offer superb handling with comfort, to be able to keep up a constantly high speed with minimal rider discomfort or exhaustion. Anyone can ride a bike fast, but to be able to do so for many hours at a time demands superior ergonomics with good suspension and smooth control harmony. Jumping from a Ducati onto a German machine showed just how horrible the Ducati was, and how I had to put twice the effort into riding the same high speeds through Devon countryside. So don't expect pure racing machines to be the fastest all the time.
Road bikes are often asked to carry touring loads, so always integrate these from the outset, and if you have a top box high in the air, then redesign.
If the luggage is well placed, aerodynamically neutral and gives a low centre of gravity, then you are well on the way to a better handling bike as you tour over the Alps.

Custom bikes.
Often stunning looks is the aim. Anything else is less.
So always aim to blow all other bikes away as mere copies and pretenders. You must sweat blood and innovation to make the machine stand out from the crowd in a custom bike show. It may be a general level of superior build of a classic design, or a completely off the wall design, but whatever it is, it must stand out in some way or other.
If you think it's all been done before, then think, think, think again.

Off road bikes.
Lightness, with strength and handling designed for the purpose are paramount. If a trials machine, then compact mass at the right position with perky handling and a grunty engine is going to make the difference between jumping up and over the rock wall or slippery river bed.
Plenty of top class suspension and dialled in handling makes a motocross bike a potential winner. In mud the engine can be tuned for grip and in hard packed earth, a perkier engine may be needed and a fourstroke is now coming to the fore again.
The ability to stand up to constant abuse makes sure a Desert bike gets the rider to the last smoke flare, preferably in the lead.
Enduros and Six day machines need all this and more, including the ability to repair a puncture in two minutes. I've patched up a broken Bultaco primary drive near the top of a certain mountain, and seen a rider of a Rokon change a primary drive torque converter belt in under half an hour.
The nice thing about making your own dirt bike is that you can decide the handling, ranging from steady for deserts, to twitchy for trials. (Note the show motocrossers who land 'hands off' from massive jumps for just how good a bike design can be. I will soon make a Sherco clone, but with a TZR motor, with two different power options using a switch, a larger tank and a slightly higher seat, so I can have the ultimate inner city 'free running' bike.)

To start at a basic level, the engine is considered first, merely as an introduction. The overall design is the most important, along with the riders ergonomics and physiogomy.
The engine is described first, as this is fairly simple introduction to going beyond the oft bland and straight forward use of engines.

So remember, that although a bike engine is just that, it's how you use it that counts.

Engines.

Many builders start with the engine.
It may be a Harley based custom, a motocross engine in a road bike, a car engine in a touring machine, or a V4 in the perfect road chassis, or just about anything else. I've worked with 30cc chainsaw engines, to massive V12 efi customs. It is all possible.

An engine needs certain aspects for a designer.
It must have the right power and power delivery, the right physical size and the right costs. Weight and style may also be important, as does certain legal requirements, often due to learner riders and perhaps insurance levels. The engine will also need a balance between light weight power and reliability and perhaps a need for various levels of modification.
A touring bike needs reliability and good fuel consumption.
A dirt bike needs low weight and impeccable power delivery.

When starting your search for the engine, go for the whole package, in both design and in building qualities. Where appropriate, make the engine an integral part of the design in both physical shape, also in power characteristics and the control required.
In some cases, the engine is core to the design, such as modern BM boxers, the 870's Norton Cosworth and the Elf 24 hr racers, where the engine is the core aspect of the design.

The picture shows an ELF 24 hr endurance racer, where the standard engine as a core component of the chassis design.
Most engines have a strong crankcase and although presumably only strong enough for holding the engine together, they are usually far stronger, as alloy castings are not only capable of holding the crank and pistons in place, but also rigid and strong enough for solo racers with the chassis bolted on as sub sections to the engine.
If using the engine as structural member, ALWAYS do structural tests before riding to assess the flexing and draw a graph of potential damage. See testing later.

Many bikes can take a wide variety of engines, especially as the sprockets are more or less in the right place, so you may with to start off with a smaller engine to test the design, with the intention to fit a better or more expensive engine once the design has proven worthwhile.
The JP7 series had a different approach, being designed to take almost ANY engine as a pod, from transverse twins, triples and fours, V4's, wankels, chain and shaft, 2WD and such like.

Most bikers still prefer an intimate and direct interaction with the engine to know what's happening and thereby control it to it's limits and beyond, especially while racing.
Most engines have standardised control inputs, but these can be modified to suit a limited range of variations. Due to modern advances, it is now possible to have minimal interaction with an engine, requiring a single touch sensitive input such as a speed requirement for the 'power delivery system'. This may be good in some circumstances, such as pampered touring machines or highly complex record breakers.

Clearly understand what is needed from an engine.
For some it is maximum power, for others reliability with fuel economy. For customs, then style or charisma may be fundamental.
All engines can be modified, not only in their power delivery, by changing between fuel injectors or carbs and different camshafts and pistons, but also in the way they look.
Most engines can be disguised or changed. Cosmetic possibilities include a belly pan or to have the pipes high, or to carve, modify or change the engine casings.
More specific variations include modifying the gearchange with power shifters and integrated kill switches and modified clutches for fast or slick gearchanges. The formula one paddle or button gearchange is now a possibility for both racers and touring riders, with touring options including electronic automatic gears.

Whatever is to be done with the basic engine choice, it must integrate into the design which improves the ride, not detract from it.

An almost ideal engine and suspension design is usually available due to the vast number of manufacturers and models. The most ideal form of engine should be carefully chosen and possibly modified to optimise the engine to match the intended design.

Do not choose an engine you cannot get or afford parts for. Do your homework first. Have a good long look at anything promising and chat to mechanics in the trade, tell them what you want. If you don't see it, they can tell you what engines are going to be close to what you need. More importantly, they can tell you what to steer clear of. Consider the format and physical shape of the engine, and also the reliability and effectiveness in the design.

When the engine is secondary to the design, then building a selection of engine models in virtual 3D on a computer is useful, so that the best engine for the design can be chosen. Alternatively a set of three tracings for the most suitable engine choices can be overlaid on scale drawings for early studies of the designs. This is always useful to help refine the real choices. See later.

Most modern engines are applicable, including snowmobile (see right) and even some car engines.
If you think snowmobile engines are not for two wheels, then think again, as some snowmobiles have demon engines, - the Yamaha R1 engine is used in snowmobiles, albeit with a torque converter auto trans and a reversed fuel injected cylinder head ! (Kiss my shinny metal snow traX !)
The Norton Wankel engine is still available as an aero engine !

Open your eyes, there IS the perfect engine out there if you look hard enough !

Like all machines, a vibration free engine is ideal. Most ninety degree vee twins and fours are acceptable due to perfect primary balance, but other twins are less ideal. Some fours have a buzzier nature, although they have lower mass deflections. Large singles often create large displacement, low frequency vibrations, which may require rubber mounting for lighter frames. Engine choice is always up to the builder, often based on racing, image and other intangibles, but frame design must be considered fully for each engine. Some engines with balance shafts are not always vibration free, merely vibration reduced. In some cases the vibration shafts may be removed for maximum acceleration.
Other concerns include heat, particularly exhaust heat, so choose an engine which has an exhaust which can be routed to clear any problems. If the engine is hidden, then consider a water-cooled engine or reliable air ducting and back up fans.

Engine mounts are important. Heavier metal structures absorb vibrations well, whereas lighter bike frame components are more prone to vibration and must be constructed accordingly. Each material, shape, thickness, fitting and such like has it's own attributes and also possible areas of concern. But like all machines, many hours of testing will be needed to prove any structure to a reasonable degree.
Metals can employ brackets, lugs and performed starting materials, usually from flat sheet or billet, with the advantages of more complex shapes and smoother profiles and transitions built up or formed by forging, panel beating etc. Forged and billet are rarely needed and can usually be redesigned, not only to be cheaper, but easier and lighter to build. When building engine mounts for a lighter structure, they must undergo primary testing with the aim of possible redesign before using the final form of the frame. I'm experimenting with aramid and rubber mounts.

Engine choice can be further refined by choosing the touring or sports versions of the engine, or the carburettor or fuel injected variants. Take note that fuel injection is not so easily adjusted and often demands a airflow sensors which may compromise the intake layout. Writing your own multi dimensional injection maps is not always possible. Some race injectors have no constraints on intake design, preferring just a unrestricted plenumn chamber, often pressurised from the bow wave, with the injector held or sometimes moved concentrically in the bell-mouth to match the pulse waves.

Once the engine is chosen, it should be run in the original frame where possible, to understand the vibrations and forces it creates. If the original frame is heavy and possibly not a good mimic of an intended new, lighter design, then it may be important to mount the engine in light rubber blocks or probably in a test piece or the initial version of the frame. This will allow the engine to be run, highlighting any problems at an early stage.
When supported freely from the roof or chairs with many bungees, the direction, magnitude and nature of the engine forces can be fully understood. This need not be done for most engines, but understanding the engine forces first hand is important for light machines with 'unruly' engines. A light frame will accentuate the engine vibrations, as there is less mass in the frame to resolve and dampen the various moving masses.
If wished, measure the forces and frequencies on each of the three axes by running the engine at various speeds.
On a rubber mounted engine, if a pencil stub is mounted on the top, front and rear of the engine with blue tack, then by offering up a note pad to the pencil will mark out the various paths and magnitudes of the forces. Do not assume larger movement occurs at higher revs, often the reverse. For most people, simply holding a loose engine on the floor on an old cushion or foam rubber block while running will suffice if needing to understand the vibrations of an unknown engine.

While the engine is out, take note of where the engine balances on the floor. Above this will be the centre of gravity. Do this again at three points to find the true centre of gravity of the engine. The centre of gravity is only needed as seen from the side for most design purposes. For an accurate position of the centre of gravity, pivot the engine on just one point, then draw a vertical line up from this point. Now do the same for another point, possibly balancing on a rear engine mount, front engine mount and upside down on a rocker cover. Where these meet is the centre of gravity. It is usually central, just above and behind the crankshaft. Try one more, different balance point to check. Mark this point from the sides and top with a permanent felt tip marker if intending to design a well balanced bike.

As most engines come from donor machines, always get the engine running before removal, so that any basic problems can be sorted at an early stage. Then loosen or remove the engine mounts, then run again to study the forces to be contained by the new frame. Leaving the engine loosely in the frame on the rear mount, then supporting it by hand at the front will allow a good 'hands-on' insight to the forces involved while running.
The largest displacement of the engine will either highlight the greatest forces or the worst mounting of the engine, probably both. Big singles without balancers are often the worst. 90 degree Vee fours are some of the best. Some boxers will suffer torque reactions in a different axis to more conventional machines.
Play around with varying the mountings until the engine is balanced such that the mountings reduce the stress into the frame. See how the original manufacturer solved any vibration problems, and consider why they chose them and if you can do better.
Where vibrations are a problem, rubber blocks or strong mountings may be needed as a main part of the frame. For small vibrations, minimal support in some planes may be possible. Although increasingly rare, if the engine has rubber mounts as standard, seriously consider keeping them.
It is not easy to finely balance an engine for a frame, but by rearranging the frame mountings in various positions, the designer can obtain ideal positions for the mounts relative to vibration and frame tube orientation, particularly at low revs.
While running, include the exhaust headers and employ token silencers, such as old socks wrapped over the ends. This should be adequate for short bursts of use without upsetting the neighbours. On two strokes, include the whole exhaust system.

Some excellent engines with balance shafts can have them removed, and my old 'Honko', (Honda XR in Maico frame, ideal for just about everything from hill climbs to swamps,) had the balance shafts removed for lightness and faster throttle response, the oil feeds blocked and ran for years with no problems. This may not always work well on all engines, so be careful. If wanting the lightest frame, and not worried about throttle response, then a vibration free engine may indeed allow a much lighter frame as it does not have to cope with excessive vibrations, but at the expense of throttle response of extra rotating mass.

Such assessments of the engine need not always be done, but looking twice at your engine allows a greater refinement, especially where used for lightness with strength. It gives a good insight of the engine forces that will need to be controlled for the lifetime of the machine, and highlights where the worst offenders are.

Partially redesigning or modifying the engine is also useful when making modular engine containment, where various engines are used.
For some development machines, a drop-in universal engine mounting system has been successfully employed for a variety of engines, as on the JP7a/b and JP8 series. This can also allow vastly easier modification and assessment of many engine designs.
For those who are lucky to have a selective collection of engines under their workbench, the machine can be designed for various engines, possibly a sports version for weekend racing, and a reliable, economical version for commuting and long distance work. As the investment and development costs are high, most manufacturers make the widest possible variations on a single basic engine design. This allows the basic engine choice to be further refined by mixing and matching sub-assemblies and individual components.

At this point, only the basic engine choices may have been made, and the basic character of the desired engine has been studied. for many designers, the overall form of the bike is still in flux, and therefore the perfect engine has yet to be defined. By being able to adapt engines, then the ideal engine is probably available.
(For the JP7 I wanted a Norton Wankel to keep the bike totally British, centre of gravity low, and smooth, but these were are rare as hens teeth, so I ended up using a VF750, also compact and smooth, then gradually adapted the design of the engine pod and rear seat to accommodate a Triumph triple, Ducati 996 and an R1.
The JP7 was then redesigned to take a Boxer motor and also a Subaru Impretza engine with 2x2 format, under influence from a local biker who uses an Impretza in his bike and I used a 2 wheel drive system through the HCS front end. The 2x2x2 format with two wheel steering was dropped, as it would have compromised the rear end lightness. I eventually resumed testing the JP7/b series with various bike engines, to prove that the pod concept worked as intended.
Some of this has evolved into the JP8 and has enabled the radical composite chassis to be even lighter.)

It is assumed that the choice of the engine will be done by the original use of the engine and possibly some modifications considered for possible modifications if required later.
If preferred, the designer can simply follow the paths trod by conventional design, using standard engines developed for metal frames which remain essentially the same, but may have just slightly different properties and construction for the specific design.

Please note that the standard engine bolt mounting holes should be used, as these are not worth the effort of modification unless making your own engines or crankcases. See later. The style and method of the brackets attached to the engine can be re-designed to mount the engine in an ideal manner regarding the engine vibrations relative to the proposed frame design.

An ideal mounting must also take into account many other forces, the most important being the power transmission to the rear wheel, (or perhaps both wheels). Some forces are not generated directly by the engine, such as when landing after jumping off a ramp and there are also the decelerating forces under braking, wanting to push the engine forward relative to the frame.

Mounting the engine can be done in many ways.
The main method is fixed to the chassis. This can be a structural part of the chassis or simply bolted in place. In some cases the crankcase may contain the swing arm mounting.

Alternatively the engine can be part of the frame, as is common in formula one, later German boxers and the Norton Cosworth, where the engine becomes a core part of the structure.
The Norton shown opposite, (Yes it is a Norton) has a very small front frame and not much more for the rear frame, and it shows that it was a full decade ahead of BMW, while the rear end showed the way for most off road and later road machines.

The well designed bike has a direct chain link, but the other part of the four bar linkage - that is between the engine and the rear axle - is not so easy and involves the need of a swing arm, frame and engine mounting so that the forces developed twist engine and rear sprocket can safely be contained and controlled. Where the engine is an active component, then all is usually well, but where the engine is passive or semi passive, then problems can arise from chassis distortion unless this is properly controlled. The plan view of the drawing will help higlight any design flaws.

Apart from a fixed engine mounting, the other main mounting is rubber mounted, or a variation thereof, where the engine is essentially a passive device when seen from a structural point of view.
For this reason, some big singles and twins often have heavy frames to absorb the problems of vibration, or to mount the engine in rubber mounts, while smooth engines often have lightweight frames, as the engine itself is often a structural part of the frame to reduce weight.

Many designers now attach the swing arm to the rear of the engine, using the swing arm bolt, and looking for such engines is often worth while, and some even include rubber swing arm mounts, although these can often be incorporated. Some designers prefer swing arms concentric with the engine sprocket.
I prefer a variation using both concentricty and widly spaced rubber mounts.

To make the overall optimisation of a design a little easier, engine modifications can include repositioning the carburettors, possibly trading off a slight throttle response for a better carb position, or perhaps improving the inlet tract for a supercharger or turbo.
Both carbs and fuel injection systems are easy to adapt for the inlet tract, so little effort is needed other than to make up a few wedge spacers or a new carb mounting.

Alternators can be replaced and a Vee belt fitted to employ a compact modern car alternator in a different position, or just to remove mass, or a jackshaft for secondary items such as a pump, possibly air conditioning for fully enclosed machines in hot climes. Jackshafts are most common where the engine is otherwise too wide, needs more generating power or needs serious modifications. See also Mead and Tomkinson's 'Nessie'.
Consider keeping the original crank component to reduce manufacturing and spares problems, but only modify the attached component to take a modern Vee pulley using car components.
Where the alternator is repositioned exterior to the engine but originally included ignition devices, the ignition points or pickups can often be repositioned on an extended camshaft to maintain accurate timing. Advance and retard balance weights are dependant upon the rotational speed, so choose and mount or modify accordingly. Most manuals give the advance curve required and a strobe will allow modifications to be checked and refined appropriately. Examples include repositioning the pick ups from crankshaft onto an extended cam shaft and modify the advance curve for the half speed or use an CDI from a different bike. See engine mods later.

Where needed for the purposes of the monograph, the assumed engine will be a modern device and reasonably applicable to various machines. The transverse straight four is common but can be wider than ideal. The main problems of Vee fours is rear exhaust routing, needing shielding and careful cool airflow to reduce localised hot spots.
At the other end of the scale, if a big single was to be used, heating problems would be minimal, but vibration may need strong mounting and possibly rubber mounted. So always carefully consider the main problems of the engine before final choice and keep them under constant consideration during the design process.

The engine will partially cause the final drive to be considered and will impose demands on the rear suspension. Chain adjustment need only be just over one pitch of the chain, which can be accomplished in many ways. Likewise, propeller shafts are quite capable of being shortened or lengthened. There is a vast number of ways to mount an engine and good design allows most ideas to be applied in most cases.

With a few final choices of engine, the rest of the power train can then be considered to match nicely with the engine.

Other components.

Always check availability of the preferred tyre choices first. Decide on the power output and choose tyres accordingly. The sizes of front and rear tyres are all important, and will depend upon the engine, use, overall design and speed ratings of the tyres that are available. The choices of tyres may be a limiting factor.

The wheel is only there as a support structure for the tyre. The tyre does the most important work, choose it well, then choose or design the tyre mounting systems and devices accordingly.

The above will begin to constrain the ground clearance relative to the drive chain or shaft angles. The JP8 had to wait almost a year for the right tyres to become available. Compromises may be needed to get the design up and running, with finalised tyres, engine performance and other refinements gradually sorted and refined at a later date.
It's a gradual process.

I hope the approach to engine choices and options has opened your eyes a little to not having to follow the crowd like sheep. Go your own path in all respects and aim towards our ideal design.

Once the basic choices are made, the next stage of design can begin, where the parts begin to be assembled as a coherent system of engine, wheels and rider.

Design integration.

Fixed. The fixed dimensions are those which due to their nature cannot be changed, the rider and standard components such as engine, wheels and transmission. Even these may need modification before a final design is made. Decide if the machine is for various range of rider and engine sizes, which size of wheels etc.
It is the fixed dimensions which often give us generic forms. Once these dimensions are chosen, they become the starting point of the design process.

Dependant. The semi-variables are decided by the design as it forms, rather than by a totally free path. This includes the wheelbase and ground clearance which can be changed within specific limits set by engineering constraints. An example is possible propshaft modifications. Time spent modifying the engine for a particular chassis design can be time well spent, likewise the wheelbase and associated axle loadings are kept within sensible constraints.

Free. The free variables which must be created in the mind are the overall form and style, colour and the many small styling options which make a machine a whole and competent device, or perhaps a complete mess, and occasionally adding the final flourishes of perfection.

A good machine is not designed overnight. If you take this seriously you will (must) be constantly changing the design and refining it. Every second you spend in the design stage will reduce grief when you start building and will save you from having to ride a less than perfect bike in the years to come. You will have drawn sketches to get your head tuned in and have a good idea of where you are going.

A very temporary, initial version of an 'ideal' layout should now be sketched out.
The sketch should include the rider, engine and wheel positions juggled and refined to fit harmoniously within a reasonable wheelbase. This will need to be modified and redesigned many times until the ideal layout and form are created. The frame, suspension and such like are definitely not drawn in yet. Aim to get sensible weight distribution while being ridden.

Only when the basics are positioned, the rider, engine, wheels and an initial assignment of overall balance, should the structural part of the frame is designed. This is how the fundamentals of engine, rider, suspension, wheels and steering are mounted.

It is important from the outset to decide where the main interconnecting forces are, and then decide how you will join them, preferably in direct lines, as seen in many beam frames. the forces from the engine to the rear wheel and from the rear wheel into the frame are very similar, but the forces from the rear wheel to the steering head are less obvious. If a hub centre design is used, then the braking forces and steering forces and suspension forces are often completely independent and the builder will be able to resolve these separately and far more efficiently for a better handling, and often lighter machine.
Design at least three completely different frames.
The non-stuctural parts will be added later, such as radiator positions for airflow refinement.

The best way to design a machine is to tie down all possible fixed dimensions and massage their relationships to create the optimised form. Once these main dimensions are sorted, the dependant variables will often fall naturally into place. Finally, the art of design can begin - to mould them together to create the best possible design, as seen in the eyes of the designer. It's called juggling the design.

Start here: Buy a roll of plain wall paper, often known as 'lining paper', a couple of 2B quality pencils, a good quality eraser and a metal tape measure.
Lightly and roughly sketch in full size the main components on the drawings. Position these for best overall weight distribution and ergonomics of the engine, wheels and rider.

For a new design, a variety of different engine profiles will be measured and made for laying on the full size drawings.

If a selection of engine shapes is hard to find, simply use a tape measure to measure the height width and length of the engines in a showroom, draw a similar box, then sketch in the approximate shapes by copying side views from magazines. This is not accurate design, but at this stage this is all that's needed to get a decent 'layout' drawing. If you have a few ideal engines, then paper cut outs in side, front and plan view makes the layout juggling process much easier. I have a small library of these for the various engines lying under my work bench.

In a layout drawing, always include the centre line of the crankshaft and output sprocket. The other plan and front shapes will then usually fall in place. If the engine choice is reduced to a few likely contenders, make basic overall measurements of the engines next time you are in the show room. You should also take digital photos of the engine mounts and any particularly interesting or annoying aspect of the engine.

Always try to measure various engines by their overall height above and below the sprocket, and also width and length from the sprocket. Four simple measurements will often suffice. For early checks, the best 'rough' dimensions are front and rear engine bolts, and the height of the vertical join in the crankcase, which usually positions the crank and sprocket. These rough dimensions give reasonably approximate sizes with which to proportion the rest of the design. Most designs can handle the slight variations from such approximations.
Shaft drive bikes are also measured form their equivalent sprocket area, and two wheel drive motorcycles such as the JPx should also have the various engines dimensioned from their engine drive shafts.

I have a full scale paper cut-out library of popular and useful engines, which allow my designs to be assessed with a variety of engines in the planing stage, so most engines can be fitted later.
If making a custom, with a bare engine, then photograph the engine from a distance on full zoom, so it can be printed out full size. This allows the surface shapes, tones and shades to be fully integrated into any final custom paint scheme.

Make sure the engine can be removed.
Avoid obstructing any maintenance paths. Classic problems include exhausts, radiator plumbing, rocker cover access, and also cylinder head and carb removal plus whole engine removal. Engines can be inserted from the side, or 'dropped' in from below, or even from the rear if the rear sub frame is removed of an otherwise enclosed box frame.

When measuring engines in the showroom, the chain offset can be guessed from the tyre size and chain gap. Engines can be moved slightly sideways for any minor problems with non standard tyres, and the rolling chassis later balanced out with positioning of batteries and such like.

Basic drawing.
Before drawing, draw the basic outline and cut the engine shape in lining paper then use this to juggle the position on the main drawing as the design develops. The rider can also be cut out in profile, with simple office tags used for kneed and hip and other limb pivots, but is it much easier to simply sit and lie on the drawing and have someone draw around you. As the rider is available full size, simply draw around yourself for perfect drawing size and shape.

Another advantage of lounging, sitting or crouching in the intended riding position on the drawing is to get a good idea of the riders' centre of gravity and also the point of weight support for the best seat and overall weight optimisation. Note where you balance on your bum, balls of the feet or knees to mark the rider centre of gravity for alter assessment of the overall wheel loadings.
Don't forget to lay your biking boots on the side view drawing for checking purposes - gearchange, brake etc.

Start with an approximate position of the rear wheel, which will then position the engine via chain or shaft.

With the engine and rear wheel, then add the dimensions of the riders profile, usually leg length and position relative to the seat, also the arm length. This is often done by drawing the rear wheel and working forwards to position the engine and rider(s) as required. The front wheel position is fairly open at this stage, having few constraints, so that the wheelbase is kept sensible with reasonable axle loading.

For conventional machines, it will be necessary to paste two lengths together to draw the side profile of the rider and engine, wheels etc. Preferably sketch from the area below with plenty of room for the engine and wheels up to the handlebars near the top of the paper.
In plan view (looking down from above) most designs will usually fit on one sheet, apart from kneeler outfits.

I have designed and built many motorcycles, from folding micro bikes, choppers, advanced composite trials machines to enclosed hub centre steering tourers, of which many have become road legal and / or have won custom shows. - But all start from this lining paper part of the design.
The large sheet of paper and a good pencil helps me to play about with any concept for a few weeks and refine the overall design, weight distribution, force resolution, weight and thereby develop various ways to overcome later design problems which would not have been seen if simply designing with primitive sketches.

It is possible to design at a drawing board, but as a draughtsman early in my engineering career, I found this totally useless, as it does not give the designer the freedom of development at the part of development which needs it most.

So leave any really accurate drawing board or engineering drawings for (if or) when they are needed, usually in detail design problems.
If you design your concept well from the outset, you will rarely need any detail design drawings, as it should all fall into place.
The only detail drawings I do are sketches of making gear change linkages of trikes, or semi active clutch (slickshift) designs and other secondary developments of any core design.
(For example, the JP8/b2 needed the gears to change without using a clutch, to asses the electronic 'paddle' concept, so I used a servo to change gear, but this was also linked to the clutch lever, such that the movement of the gear lever up a gear would intermittently kill the engine, to drop revs, and on the up and down shift, the final section of the clutch movement would be damped for smooth engagement with the engine revs. This needed a simple linkage which activated the clutch with the gear lever, yet be adaptable on the test area. The final design was a ramp and dual pull bar arrangement to the clutch linkage which I could easily adjust from the riding position, with an adjustable release valve for setting the changes smoothly. - This is where real detail design is needed, not in exact engineering drawings, but in engineering sketches which develop and vastly improve the general ideas before committing to metal and composites.)

I use computers a fair bit, but they are only tools to help the design process.
As such, my engineering drawing software rarely gets used in preference to development tools such as 3D graphics software such as Lightwave and Autocad. This allows the designer to visualise the design in such a way as to get the overall design correct first, and to worry about detail later. If all the fundamentals are correct, and well thought though, then the rest usually falls into place with few if any problems.

Computers should never replace pencil and paper, but merely complement them.

An aside on computers. If preferring to use a drawing package on computer, then simulate the paper process. Although computers are superb for refinement, they cannot replace the paper and pencil stage. There is no substitute to handling real, full size drawings and the feedback they give.
But computers do have the advantage of allowing the designer to model the design in 3D and view it from all angles, to see faults and possible places of conflict and infinite refinement. Both paper and computers have their uses and both should be used where most appropriate. But being a standard fifty percentile male and simply inputting this into a computer is missing the whole point of design. Design is an art.

As computer skills are gradually built up, a library of virtual objects will accrue, such as a variety of engines, riders, standard brake components, wheels and ancillaries such as carburettors, fuel pumps, headlights and such like. I have many engine modelled as 3D Lightwave objects. Likewise riders, wheels and such like. With this, I can simulate a basic working design in an hour or less, and from this, refine the design before setting to work with paper and pencil, then saw, file and welder.

There has been much debate on the relative merits of the various approaches to 3D drawing packages:
Choose the software carefully and decide whether designing a bolt or are creating a work of art.
Always see any expensive software in action, or preferably use it first, as many programmes have attributes making them ideal for some people and atrocious for others.
Although dimensionally based drafting packages are the seemingly natural choice for designers of machines, they do not have the flexibility of 3D packages such as Newtek's superb Lightwave. 3D has enabled many fine machines to be created and greatly refined in metals and composites.
The authors university computer aided design (CAD) and Autocad courses were rarely used in preference to Lightwave learnt at home. There are many simpler and cheaper 3D packages and many will also do well, as you rarely need all the bells and whistles of a modern 3D package. So the choices are personal preference or availability.

Engineering drawings are not so useful as 3D modelling which can greatly help refine an idea, especially where components may come into conflict, such as viewing exhaust runs through frame tubing, steering linkages or items which move relative to each other then rotating the virtual design to asses the many and differing potential problem areas.
Inverse kinematics is useful for refining complex steering and suspension systems or getting the riders to fit.

If very keen, the ability to export work between various packages such as drafting and finite element analysis should also be checked prior to purchase. Data transfer is particularly important due to the steep learning curves of some packages, should the reader wish to become deeply involved in the design process. Therefore always carry a floppy disc with a test piece, to check it transfers easily and correctly. A basic autocad format is still the most popular interchange format. The test piece can be generated on the first item to be tested.

Fundamental engineering is easily accomplished with or without a computer, but the overall final form, shape, style, colours and final detailing of the machine are usually very important, and more easily accomplished is it can be studied on a 3D software, or on a clay model. Computers are simply damn easy to play around with for colours, shapes and overall styling effects, as seen from various light sources, colours and angles. Here the JP7 has a small front rider and a very tall rear passenger, to get a rough idea just how good or bad the design would be.

A personal viewpoint.
The above may be controversial, as many designers will offer the standard reply - that building a mechanical design requires mechanical drawing software. This is often a trap, as the actual design is never done on the computer, but with common sense, sketching a frame tube on a full size or scale drawing is often better and quite good enough for most purposes. A bike is not an oil rig or aircraft, and therefore does not need a set of working drawings.
Even if a design is to be mass produced, a simple jig from the original machine often suffices at his level of engineering for a few hundred machines.
Therefore do not get side-tracked by having to spend many hours making technical drawings. Do not waste time making overly accurate or neat drawings where true design should be done more productively elsewhere in the design process.
As an engineer and draughtsman I have seen both ends in the marine, nuclear and other industries and know first hand that good designs come from varying from the drawings, often just slightly but sometimes throwing the drawing away ! This is why Japanese motorcycles are superbly made, but are absolute buggers to service, and rarely match European designs for handling and general ability to maintain. The Japanese have now realised this and take both approaches to achieve excellent results, but the home designer and builder has far greater freedom of a massive design team with conflicting needs and a strong tie to drawings, which ultimately constrict a design if not properly (ab)used.

A draftsman is a person who does accurate drawings for other drawings which are often difficult to modify. Whereas a designer is a person who does not need such drawings, as they know how and why the design is taking a particular form. Any drawings or sketches done by a good designer are merely to check some ideas can work as intended, and to measure certain hidden parameters such as weight balance, steering lock or seat position. These are then passed on to others to make.

YOU are doing all this, so drawings are NOT needed to pass on information, merely to check your ideas will work.

Such sketch drawings may often be full sized for ease and need be no more accurate than is needed for the purpose. As the designer is often juggling these aspects of design, a very messy drawing with lots of rubbing out and sketchy lines, shows that a lot of true, innovative work is being created. A single sheet of sketches may contain the nucleus of many machines.

Lining paper is very cheap. - Motorcycles are not very big.
So always use the ability to draw at full size to advantage. It also makes the process faster and far more accurate where it's needed - in the overall design.

The most important skill is being able to use paper and pencil. This works perfectly well for most people and it still remains the definitive design process for innovation. Carry a small note book and pencil when testing and riding.

Where to start?
Begin drawing with the rear wheel, then position the engine according to the transmission requirements. This will take into account the suspension movement and ground clearance, the best pull of the upper chain run under power to prevent rise or squat.
A selection of engine positions should be considered for weight balance.
Then the rider(s) positioned, possibly for ground clearance and / or low centre of gravity.
Only now can the front wheel positioned for optimum weight balance.
The front wheel and also the engine and it's associated swing arm pivot will move fore and aft during the design sequence to refine the overall balance of the machine, especially if the wheelbase is to be kept within suitable parameters. Remember that this is initial rough sizing of the general design, not any finished object.

Once the engine, wheels and rider(s) are positioned, then work out the best shape for the frame, with careful attention to the overall balance, strength and good positioning of the swing arm pivots and shock positioning.

The rider(s) should also be positioned for best ergonomics and control. Motorcycle riders position is vast, from full racing sidecar 'kneeler', to full recumbent 'street luge' style and just about everything in between. If needed, lie or sit on the paper and draw around the rider. Likewise for the engine.

The more you use a rubber (eraser), the more the design will gradually be refined. Sometimes my drawings are so badly eroded that I have to start a second or third new sheet. It saves a lot of cutting and welding later.

When positioning the engine, ensure the chain or shaft is fairly parallel to the engine and swing arm at mid position of the intended wheel travel. Slight rotation of the engine around the front sprocket can be applied to a chain drive engine to massage it into an optimum position. Do not compromise oil level in the sump, as excessive deviation can cause oil level problems. The new Ducati deep V sumps are excellent designs. Make note of the new oil level and mark it on the actual crankcase with paint and modify the dipstick.

When seen in plan view, the engine can be positioned off the centre line to get the chain to align with rear sprocket and tyre clearance.

Once the rider and engine are decided for approximate optimum form and balance, they can be drawn a little more accurately so that mounting the centres of gravity can be more closely assessed before finalising carb routing, exhausts, mounting holes and brackets.

Draw side, plan and front drawings.
These are easily generated from the first drawing and will highlight the many problem areas such as chain alignment and cornering ground clearance.
The frame is NOT yet being drawn, as there are many aspects to be considered before simply joining with tubes and such like.
At this stage the ideal layout of the machine and rider(s) is being created. The wheelbase, engine position, rider seat profile, foot rests and handlebars. Lie on the drawing to sketch around the rider, and use your motorcycle boots for helping to refine the placements of the various components.

No apology is given for getting the reader to draw full size in this seemingly barbaric manner, but this is real design for a real world. One may now be able to see limitations of computers and drawing boards. The ability to draw full size helps greatly in understanding the process as a whole.
Surprisingly few professional designers bother to start with reality, with users all too often suffering the consequences. All the finest drawing boards or computers in the world will never allow the reader to measure and assess their components such that they will be ideally positioned.

Position the drawing vertically and check for seat height and general riding posture.

Being a fifty percentile male may work well when designing theoretically from reference books. But reference books, for all their good intents, can never do much more than justify their contents academically when the inevitable problems arise. Always read reference books and learn from them, but the reader need not follow them blindly. Reference books are read by innovators and followed by sheep. Likewise, if this text is not offering a path that the reader seeks, glean what is possible, then break away and go for gold.

Designing the machine.

A few of my favourite quotes to help set the stage.
'Statistics in the hands of an engineer, are like a lamp post to a drunk, - used more in support than illumination.' (A.E.Houseman.)
'Engineering is the imperfect in search of the perfect.'
'Engineering is doing for a few quid, what a corporation needs thousands of pounds to do.'

Design is a natural process.
From the initial idea, to how it will end up, the designer should always be open to new ideas. Also know the possibilities and limitations of the various materials as you read though this and other writings. If in doubt, refer to hands on assessment of various conventional machines to see how the materials and construction methods can be applied to the new machine.
Consider many options and sketch them in lightly, and if seemingly good, leave them on the drawing as many other avenues are also explored. A good drawing should have the genesis of many excellent designs.

An initial 'ideal' layout should now have been sketched out on the main drawing, with the rider, engine and wheel positions juggled then refined to fit harmoniously within a reasonable wheelbase. The basic frame design can now be designed and refined.
If no frame is yet designed, then the design opportunities are much wider.

Note, consider and assess the following;
There are no fixed rules. (If pictures of the JP8b/c ever get published, you'll understand !)

The frame and suspension is often a beam or series of beams supporting the rider and engine upon front and rear wheel axles.

The main supports acting on the frame will be on the rear swing arm pivot and rear shock mounts, and usually the steering head. (Hub centre steering designs may well use a front swing arm and shock mount.)

The overall load acting on the frame will mainly be a combination of rider(s) and engine weight.

The wheels will tend to want to spread apart, under the influence of fork angle and rider weight. (Not always so applicable to hub centre designs.)

The whole structure will flex, possibly imperceptibly. It is not always nice to ride a flexing frame.

The main forces acting on the frame from braking will be to push the engine and rider forward relative to the decelerating machine.

On chain drive machines, opening the throttle will try to bring the engine and rear wheel closer together.
The chain runs must not foul the chassis or suspension for reasonable clearance as the chain flexes up and down, possibly with an asymmetric distorting force in the frame and swing arm under acceleration.
The forces applied to the frame via the transmission will vary in many ways and relative to the gear ratios.

The forces applied to the frame via the terrain will vary in many ways and relative to the speeds and undulations and mass of the unsprung components.

Ensure handlebars have ample clearance for hands, cables and steering linkage(s) and must not compromise any components at full lock.
Ensure handlebars and foot components can be easily replaced after damage. Handlebars and footrests can be designed such that they absorb energy and deform before the frame or engine becomes damaged, acting in a sacrificial manner to save the main components.
Preferably allow peripheral components to deform enough during a simple fall to allow the machine to be ridden home.

The brakes will pass forces into the frame which must be resolved safely, especially during emergency stops.

There is the need to support the components with metal, (usually tubes) which is not completely tolerant of excessive or compound curves.
Compressive loads tend to collapse a thin or weakly supported area.
Sharp corners can lead to excessive stress points.
Purely tensile forces may permit a thin component to be used, but the forces must be properly resolved at each end.

An idealised shape, often created for aesthetic reasons is not necessarily good structurally.

Safety.
In a crash, do not design anything which will unnecessarily injure the rider. Consider carefully what happens in a front end, side or rear end shunt or crash and also while sliding down the road.
If the machine is to slide down the road, ensure the contact patch on the road can act as an anchor to slow the machine down. When sliding, try to design the sides of the machine to lift the tyres off the road surface, so a 'high sider' flipping of the machine is greatly reduced.
Many bikers loose their legs at low speeds, so integrate side or engine deflection where possible, should they slide into a lamp post, an opening car door or similar obstruction.
In a front or rear end shunt, a swing arm, fork or other main component should remain in place. If any suspension component should fail, it should protect the rider from further damage.
When displaced, the rider should ideally be moved over the crash obstruction and away from damage on the machine or other obstructing influences.
If the machine is a recumbent, the front end crash can often be as safe as a car.

NO component should be designed such that it can fail in a dangerous manner, either in a crash or from poor design or from fatigue.

By the very nature of human design, failure will occur, but all possible failures should be carefully considered, then, should it fail, it must be designed to fail as safely as possible.

Weight balance.

At a basic level, the classic weight balance is often around 55/45 percent rear to front, and is common on average machines. Even formula one and many other divers machines rarely diverge from this common ballpark balance.
Drag machines, choppers and such like excepted.
Always design the machine with the rider included in the overall weight.

A basic example.
If the front needs a third of the weight, then simply position the combined weight of rider and engine two thirds to the rear of the wheelbase. This use of numbers is very basic, but works reasonably well.
The further a load such as the rider is from the front wheel, then less of this load acting on the front wheel. Loads to be calculated are usually the rider(s) and engine. The frame weight usually halved and assumed on each wheel, as the tubing, forks, wheels and minor components are often fairly evenly spread between the wheels.
For initial assessment of the intended wheel loadings, then these simple calculations will arrive in the ball park. The final measurements are done on scales and adjusted later.

To use very simple arithmetic, the distance of a load from the front wheel, when divided by the wheelbase is the proportion of that load which is supported by the rear wheel. -

If the engine is two-thirds of the wheelbase towards the rear wheel, then the rear wheel will support two-thirds of the engine weight.

The distance from rider to front axle divided by wheelbase equals the proportion of the rider on the rear wheel. - This gives the amount of rider load acting on the axle.
Similar can be calculated for the engine.
Add the loads of engine and rider on each axle, plus half the frame weight, plus the forks or rear suspension and a wheel for each axle, to find the approximate loads acting on the ground under each axle.

Weigh the engine, rider etc, bathroom scales usually suffice. Note the weights.
Now choose a ballpark measurement for your wheelbase. Measure the distance of the centre of gravity of the engine from the front wheel.
Use a calculator to divide the distance to the centre of the engine from the front wheel by the wheelbase. This will give a percentage. Possibly 0.95m / 1.75m = 0.54% of the engine weight on the rear wheel or something like this. Now multiply by the weight of the engine. This gives the weight acting on the REAR axle. (As pivoted around the front axle. See 'moments about'- an engineering term for calculating loads).
Now do the same for the rider(s)
Add up the weights on the rear axle. The remainder of the total weight of the riders and engine is on the front axle.
A good designer does the same from the other end, to check the loads do indeed add up.

This first calculation may be far from what is needed for your axle loads. Some initial loadings may be horrendously poor, so check the centre of gravity of the rider and engine on the drawings. Juggle the positions of the engine and rider(s) until it gets close to what you need.
It is common to design the axle loads with a single rider for a conventional motorcycle, as the passenger is often close to the rider and the overall effect is not much different.

The even distribution of the frame and ancillaries will also help ameliorate the overall weight balance, but a good designer will not rely upon this at this stage. The fuel tank when full and if positioned badly will also affect the weight balance.

If making MANY changes of the design, moving the rider and engine around, then it may be worthwhile marking equal spaces between the axles and noting their axle loading values. By using this simple positioning, most of the complex calculations can be circumvented. Divide the wheelbase into half, then quarters for 25/50/75 percent etc. to make calculations easy. The cut-out engine sketch and the eraser will be put to good use at this stage.

The weight of the rider can be calculated onto each wheel, then the amount of weight of the engine and any other heavy components, the total on each axle can be calculated and assessed. Calculating the moments about points in this manner will manage this problem in comparatively simple manner. (Far easier than cutting and re-welding later).
On complex machines, writing of a simple spreadsheet will greatly assist the refinement process with minimal manual calculation. It will also show up the differences between solo and dual riders with different masses, allowing the balance to reach an optimum under all possible scenarios. In such cases, two sets of calculations will be made, so that solo and dual riding can be compared for unwanted imbalance. In such cases, a compromise is often reached after a dozen attempts.
The JP7 series used spreadsheets to resolve the best axle loadings with solo and dual riders, both with and without luggage and the prototypes certainly handled very well from the outset when road tested.

Also include luggage and fuel if they are not half way between the axles. Standard small aircraft practice often positions the passenger close to the centre of gravity to minimise any upset in balance during solo or dual use. This is not so easy for a motorcycle, but the general principle is sound. This is why the JP7 has the engine to the rear, so that both solo and dual rider situations retained impeccable balance at all times.

Having to modify wheelbase to get the loadings acceptable will be a lengthy process, so start by deciding the best wheelbase, then modifying wheelbase, engine and finally the rider position. Although the rider is a prime design consideration, the rider can be repositioned along the machine by a large margin, to allow fine fettling at a later stage. This is because seats are often added at a late stage in the design, allowing excellent refining of balance to the rolling chassis, while on bathroom scales. Do not leave the problems of balance until later, as the wheelbase, engine position and general balance of the machine should be done before the frame is designed, not later. See also seats later.

It may seem an annoying process to measure the rough axle loadings but this is paramount to getting a good handling machine and is very important when designing radical machines from the ground up.

For those wishing a more pragmatic approach, simply use a plank of wood slightly longer than the proposed wheel base to represent the bike, use broom handles or rods to represent wheelbase axles and measure upon two bathroom scales, then load on the engine and riders and adjust until the required axle balance is attained. The riders must stand on the plank in the positions of their centres of gravity as if on the machine, therefore their weight is often placed above the seat area, not the footrests.

Record measurements on the main drawing both numerically and by sketching. This is to compare with the final machine for future feedback and is the secret weapon of good frame designers. This feedback helps refine the designs as future frames are developed. This is important, as although some machines vary only slightly, some can differ wildly from the intended measurements, especially when designing and then building for the first time.

Massaging the design can refine the axle loadings, but there is not much movement to play with regarding lightweight machines, so wheelbase, engine and rider position are the only real variables. Time spent here is well repaid. Minor refinement of the fundamental rolling chassis can be done by arranging the batteries and other accessories.

Consider a wheel base no longer than needed for the purpose. The weight on the wheels must be appropriate to their sizes and ratings. A small front wheel can often carry a similar load as a large wheel, although maximum speed may be less due to tyre technology. Gearing, especially if shaft driven, may limit the diameters of the driven wheel(s).

Wheelbase is a moot point with at least one designer saying that bikes need longer wheelbases. The author disagrees, having built many excellent machines with very short wheelbases with no untoward problems other than during braking and accelerating with a comparatively high centre of gravity.
Most handling characteristics are wheelbase independent, unless extremely short or long wheelbases are considered.
Always aim for sensible wheelbase, not too long so that the machine will be unable to turn easily in tight traffic, where a motorcycle has many of it's main advantages. Likewise too short a wheelbase will accentuate pitching of the bike while braking and accelerating, especially with conventionally mounted riders. The lower the centre of gravity, the shorter the wheelbase can be without pitching and associated problems under braking and power.

Short wheelbases are ideal for trials bikes, whereas overly long wheelbases simply make for an unwieldy and difficult to manoeuvre machine. A long wheel base is fit only for a two wheel limousine which is not expected to negotiate very tight traffic, or drag bike, hill climber and other extreme or unusual machine.
As the centre of gravity is lowered, then the wheelbase can be decreased while maintaining acceptable pitching of the machine under braking. If true antidive is available, as used with hubcentre steering, then the wheelbase can be even shorter. For a recumbent engineered with true antidive hubcentre steering, then excellent stability with superb, sharp handling and superb slaloming ability is much closer. I know, as I've built and enjoyed riding many such designs along fast, twisty roads.

Think of at least three designs for the proposed frame, one of which is extremely radical. It is very important to create three different frame designs. At least one should be extremely radical, - real 'off the wall', 'blue sky' thinking. The final form will often be a compilation of all three.

Find at least three or more major problems and consider how they can be improved. If you find no problems, then you may be either a good designer, or not looking close enough. Use an A4 sheet of paper to sketch out various ways to improve the problem areas. In some cases, the problems such as how to cross brace the rear engine mounts or suspension support tubing may be drawn in roughly, but only finally decided once the main frame tubes are in place. This is because much of the design can be refined as it evolves. But it is always important to get the main frame tubes drawn as intended, and the general layout of the suspension and engine positioning relative to the swing arm pivot.

Once the details of the various components are contemplated and lightly drawn onto the paper, the general form of the frame can be envisioned.
The long revision part of the design process can now be started, which is never ending.
The final stage of this design process will be decided when the extra time spent is no longer outweighed by the level of refinement. All concepts should be considered at this stage.

Where any rear shock unit is mounted at its top, the engine mounts may not be far away, so these could be integrated into a single strong component with the rear swing arm pivot, following common motorcycle practice. Keeping many of the main load areas close together often makes for a stronger, more rigid structure with less weight. This also minimises the effects of manufacturing inaccuracies when under load, thus reducing flexing during riding. For generic examples, see 1998/2002 alloy beam frames and their alloy cast swing arm and engine mounting areas.

The conventional shock absorber is a damper unit with integral compression spring. How this is compressed will depend upon many factors, some to advantage, some not. As most vehicles expect to absorb minor road irregularities constantly, then the initial movement of the shock should be supple. At the maximum movement of the unit, just before the hard rubber bump stop comes into play, the forces will be the maximum normally permitted by the designer. Suspension movement will differ from motocross to touring to racing.
Between the suppleness of the initial movement and the firmness of max movement should lie a gradual increase in spring rate and damping resistance.
As most shock units use constant wound springs, (rather than compound wound) any geometric increase in spring rate can be done in the geometry of the shock mounting. The normal method is to have the shock mounted such that at maximum compression, the forces are working directly in line with the shock movement. At supple positions, as normally at rest, the shock can be at a less effective angle, not at ninety degrees to the shock movement which allows a more supple movement. The refined use of angles should allow a more advantageous use of the shock.
The use of rising rate linkages can also be applied, but usually they are used as found by the manufacturers of such items, as there is no point in reinventing such systems. As such linkages also take a high loading, the original equipment and linkages makes reliability and spares much easier.
Leaf springs and other types have been used in the past, but the standard concentric damper/spring unit seems here to stay. Shocks can be separated for ease of development, but as they are compact and easily adjustable, are not usually worth the extra effort.
Separation of the spring from the damper is only necessary in unusual designs, such as the interactive, linked suspension as used on the JP5 series for linked anti dive and anti squat. See also suspension later.

As there are dips in roads as well as bumps, the suspension is usually set up with a slight amount of initial sink while stationary. Therefore the shock and forks will be slightly compressed when in normal static ride condition. Ensure this does not upset ground clearance.

If building dual beam 'wrap around' frame in alloy or steel, there are many extruded sections available in thin wall box sections in steel and also in various forms of aluminium alloy. These can be reshaped but care must be taken to ensure gentle curves which do not get close to any dangerous distortion or failure point. Test for this by sacrificing a test piece until it creases or otherwise distorts. Measure the amount of distortion by the forces applied and simply measuring the physical deformation, then design the fame so it only applies minimum distortion required and never exceeds of two thirds (preferably less) towards the distortion when tested. This must always give a safety margin during the worst case of use on the road. The forces used to shape the tube should be much higher than those found in normal use on the machine. (And preferably at a different, safer angle.) See also load testing later.

If not confident about materials, their dimensions and wall thicknesses etc, then reference the intended design against conventional machines and follow standard industry practice until experience shows otherwise. Most second hand bike dealers will have a scrap frame that can be cut up for reference. If a donor machine is used, then careful removal of fittings such as engine mounts will allow close study of the materials, whether the tubing is seamless or is the cheaper seam welded, or possibly double walled, and a host of other aspects such as where the rust begins. Conventional four-tube frames in steel are easily referenced against standard machines for dimensions and wall thicknesses of the materials.

The frame and suspension can often be seen as primarily holding the wheels together, while supporting the distorting load of engine and rider under the highest loads, such as landing off a drop or Postbridge. The frame is then refined to support the engine and rider in such as way as to maximise the potential of the design. This usually means minimal longitudinal, lateral, vertical and torsional distortion of wheel alignment under all conditions.

As many builders wish to employ non standard designs, they often need to understand the advantages and disadvantages of the new ideas available.
For example, the single sided suspension design is becoming popular at time of writing. Frames with single sided rear axle support usually require a live rear axle which must allow the power to pass from the sprocket to the rear wheel. This will depend upon a variety of engineering variables. Whatever is designed, it usually (but not always) means a live axle with one end demountable for the bearings to be fitted. This usually implies splines or other form of concentric shaft power transmission.
There is no real need for single sided designs unless for a good reason such as styling or ease of wheel changing, such as the ELF 24 hr racing team, or asymmetric frame design. As an engineer, I almost always take the single sided design approach, because I often use asymmetrical frames with single sided hub centre steering, where one half of the frame is essentially a passive component.

Consider the following:

The advantages of dual sided wheel support. (Standard swing arm.)

The wheel is evenly supported across the rear of the frame.
Allows standard wheels and mounting components.
Simple to build and align.
Resolves suspension, accelerating and braking loads evenly into the frame.
Can be lighter.
Failure is often less dramatic than single sided.

The disadvantages of dual sided wheel support.
Requires alignment of more than one axle support component.
Requires properly aligned and adjustable support for chain adjustment.
Dual chain tensioners can allow poor wheel alignment.

The advantages of single sided wheel support. (Elf, Ducati, Triumph etc.)

Can allow easy wheel and/or tyre removal.
Offers greater room for panniers.
May offer easier chain adjustment.

The disadvantages of single sided wheel support.
Poor design can cause distortion under loading.
Requires much stronger component design and sometimes extra weight.
Requires special wheel, axle and wheel mountings. See making live axles later.
Failure can be more dramatic.

Both can allow a design that pivots concentric with the engine sprocket.
Suspension is discussed later.

If in doubt when designing the frame, consult others with experience of such structures. Do not simply copy machines which may well use more complex design and construction methods, unless the design has been carefully considered.

Along with wheels are the brakes.
Brakes must be considered as an important part of the interface between wheels and frame, as they connect both the wheel and suspension and occasionally frame, at points of high loading under braking. Always insist on two separate braking systems acting upon different wheels. See brakes later.

There is much to consider for any frame, but only when the engine, rider and wheels are drawn in position can the final assembly be decided. Strength and safety are the main considerations. Consider each part of the design from side, front and plan views as they are drawn.
When designing and sketching, what is required is good, honest, applied technology on paper, not an oil painting. It is much better to have a well thought through design with many changes and modifications than a clean or pretty drawing.

Leave the design for a few weeks so ideas can form and refine. Make notes. Do not, under any circumstances skip this part of the process. Playing with modelling clay to contemplate 3D styling ideas is worthwhile in a few cases. A heavily loaded wire model using paperclips and solder can highlight frame areas of concern. The use of CAD can help refine ideas, although the best in this situation would be a 3D modelling package. This will allow the sculpted forms to be viewed in 3D with modelled rider, suspension, transmission, many possible frame designs and a host of other variables which can be dynamically revised until a refined, optimised form evolves. If finite element analysis is available, it should be used to minimise areas of high stress.
Always copy ideas generated on a computer onto the paper to double check the design. What looks great on a screen, can offer unwanted surprises when transferred full size onto paper.

For those who are aiming for weight control, then without weighing anything, make a rough guess of the preferred weight of the complete machine. Take conventional machines as a reference point and work backwards. Once a ball park weight is decided, write it down. Do not be too optimistic first time. Now segment each part of the design into estimated weights. The engine, wheels, forks, chain, sprockets and other fittings are measured by simple weighing on bathroom scales.
From the remaining weight, decide the proportional weights of the frame, wheel supports, seat, handlebars, steering head and other components that have been assembled. The frame components are often just a minor part of the overall weight, and greater weight reduction can be via lighter components. Do not try to get weight lower by compromising the frame design.
Write all this down for consideration and future reference. If the machine looks likely to come out slightly heavier than expected, do not worry, this is not unknown for a first attempt.
Building to a strict weight limit for a first design can often lead to quick structural failure. Many bikes do not loose weight only from the frame, but on lighter ancillary components, or removal thereof.

Subtlety of design does not happen overnight.
Aim for a safe test machine at first.
Non-destructive and destructive testing can help decide where weight can be removed later. See testing later.

An aside on subtlety.

Any damn fool can eventually build a fast machine, or a big machine or an expensive machine.

A real designer builds a far better machine.

Control harmony acts at all speeds. At low speed control is fairly light but subtle, allowing quick manoeuvring. This gradually changes towards top speed which is more stable with full feedback, allowing confident quick line changes.
And it does it all with the minimum of hassle.

When one gets the fundamentals right, chooses sensible components and their arrangement, considers the design fully and does not compromise, then excellence will often follow naturally.
A well designed machine, with the right balance, structure and components, can then be further refined and fettled to be a superb machine. A poorly designed machine with inherent faults can only be second best, no matter how much fettling it gets.
This is not to say that any well designed machine is going to be superb, - far from it, it also takes a certain magic, a dream, a certain feel for design and knowing where a possibility may end up, worth following and when to simply 'suck it and see'.

One of my best handling bikes ever, was built simply to assess a certain aspect of the JP series. I have yet to find the perfect front brake for it, even after ten years, so this has gradually made me design and build my own composite disc brakes !
Follow the dream.

It is assumed that if wishing to build a particular type of machine, the reader will have ridden a number of similar machines. When designing machines, especially those requiring the subjective needs of good handling, then the designer should begin with a fierce approach to the prime purpose, only ameliorating the form to fit the real world.

Like most bikers, I've ridden a wide variety of machines and naturally know when a good bike appears. The art of test riding is always personal and always recommended. I have ridden appalling machines and some truly superb delights of mechanical perfection. I recommend all designers and builders to follow suit, to understand what they are riding, - and why it is like it is, for both good and bad.

In amongst this design route, will be a path towards perfection, or as perfect as the concept can be. Knowing where to look and where to tread is not so easy and takes lots of experience and / or luck

Sukoi's Fulcrum, possibly the worlds finest air superiority aircraft, began with the Russian designers just creating the most perfect wing. Only then were added engines, nose and controls to see how much the ideal wing was compromised.
This is an excellent way to build a motorcycle.
The perfect layout, possibly for trials, with the need for lightness, twitchy yet delicate control and massive ground clearance - somewhere between a gymnast, Rugby player and a ballerina.
Or touring, with a totally relaxed seating for two with relaxed, stable control geometry. Many hours of true comfort.
Or racing, with maximum aerodynamic efficiency and adaptable handling for various circuits. Precise yet confident.

Compromise begins with chassis and suspension.
Then often ameliorating this by test loading the core structure to reduce distortion until the best chassis is possible. Finally the design is further refined by compromising the design with the necessary 'secondary' components but in a manner to minimise the amount of compromise to the potential ride envelope.
After that its just a case of fettling forever, or if it doesn't work, get others to ride and assess, then back to the pub and drawing board.

It is often advisable to see the design from a different perspective.
For motorcycles, there are many ways to see a machine as an interactive device. It is recommended that the designer finds the local gliding club and gets a flight in a modern machine. The costs are not expensive and a single days membership will be well rewarded. Get a feel of the machine once relaxed, especially after a winch launch :{ The lack of power heightens the subtlety involved, helping to understand the purer delight of good control harmony. Use this understanding as a reference point when testing the design.
Also consider assessing the ride of motorcycle trials, motocross, slalom skiing, street luge, wet biking and surf canoeing. The main reasons of study are using light machines which encourage total user input at a high and very tight level of integration. Warning, these experiences may cause you to daydream while at work. I found that trials helped me ride my Duacti far faster around twisty roads, especially where the surface was poor. Ice skiing also helps improve your off road balance, especially in winter, such as riding across Hardknott Pass when it's closed off due to snow drifts.

The above is just one design route, with the rider as the prime component.
Alternatively, uncompromised machine-based approach is ideal for racing, where the rider is merely the primary initiator of the control systems such as racing or world speed records.
For touring, rider comfort should be the central consideration.
Converging both approaches will lead to a superb machine. This can give a series of very comfortable, fine handling machines with superb long distance ability yet with excellent slaloming capability. The wider possibilities for superb control harmony is another of the major lessons learnt from my machines. Innovation gives excellent insights into many areas of the ride envelope.
All machines will differ, so the reader is encouraged to aim to discover their own new fields of two wheel delight, - there are many.
You may wish to make a research machine first to test a few radical ideas, then test to see if they actually work. From this, the machine can be adapted into a bit of a hack as it evolves, then the final machine designed using this improved information.

(Along the JP1 to JP7 series, I have constantly worked towards hands off stability down to walking pace, to roll to a standstill on these machines with no need to touch the handlebars. It doesn't always happen, but it's often possible. The JP4 has been tested in Llanberis Pass and in France, where it handled far better than any of the many Ducatis I have owned or tested, be they at Silverstone or in the Alps. The hands off stability at top speeds is also important to the overall work, to the point where the JP6 handles perfectly, across grass and rough roads, and hands-free down a very long and steep hill with tests including almost zero steering head rake angle and almost zero trail, to handle extremely well, responsively and with no twitches or vices whatsoever. When this happens then you know the design is about as good as it gets. The JP8b/c series is designed and to improve on the JP6 work, but with idealised wheels and composites, so it can be applied to the final leap of the design process. The last stage has been proven with the JP4d and JP6c series and the JP8 is getting close to a new level of perfection on two wheels. Personal viewpoint only.)

Most motorcycles are a vehicle with a rider perched on top, ideal in the days when horse riding was prevalent and people knew no better, and quite adequate for an era when kick starts were common.
Today, there is no excuse for such an archaic approach to the rider of a road machine. For road machines, the future dawns a little less blinkered, brighter and more ergonomically appropriate.

While refining the design, consider how the rider will become part of the machine, relaxed, all controls acting naturally and easily. This integration of the rider will require adaptability in the early designs. Such ideas may include a selection of ratios in the steering linkage of hub centre steering designs, adjustable rake and trail, suspension settings, seat position, handlebar angles. A host of other options to help a machine be fettled before it becomes close to an ideal. Many of these options are not so easily adaptable with traditional front forks. A few ideas to help develop research machines are given later.

Remember that a motorcycle is a powered two wheeled machine to transport a rider as comfortable or as fast as possible. There are a few engineering and handling requirements as mentioned later, but everything else in the description is open to individual interpretation.

And so back to the drawing:
On the drawing, as the main structural areas are marked and gradually refined, such as steering head, engine mounts, rider load points, also mark in the forces of both the static loads and under full acceleration and braking forces, and when landing off a jump. Mark them in as arrows, to maintain the most effective use of such drawings. Making the arrows proportionally large to the forces will help direct the subjective design of the frame form and structure. A yellow felt tip highlighter pen will allow drawing to be modified over these underlying guides to maintain an understanding of what will happen in the structure as it evolves.

By this stage, most readers are already considering copying a commercial design of frame and is the common way to build their first machine from scratch. Such limits are usually drawing the engine and sketching the best looking frame as a starting point. Then following commercial practices and their tubing sizes and materials. Most manufacturers usually employ ordinary materials. (Any half decent manufacturer would certainly advertise the hype value of any exotic materials in their frames. - Just cut up any commercial bike to see the 'adequate' quality of materials used.)

It is quite common for most 'custom' builders to simply follow standard practice and copy a commercial frame design.
This is not required for the innovative builder.
By standing back and looking at the full size drawings in a general, open minded manner, a design should begin to form naturally as the builder recognises the mountings of the engine, suspension and rider and forces involved. Just thinking through the shapes in the mind will gradually consolidate a basic frame. This can be sketched in and refined with the problems such as engine mounting, exhaust routing, rider mounts, shocks and radiator airflow. There may often be a natural line or triangle between the headstock, shock mount, engine mounts and swing arm pivot / engine sprocket area.

Simply positioning the engine, frame and rider, then connecting with a frame using standard tubular steel techniques is a terrible loss of opportunity. If this is to be a machine optimised for a particular owner and rider, then build to optimise the design rather than follow other designs.

Always think of at least three different options. One design at least should be totally radical, without consideration to anything other than fundamental engineering, perhaps not even that. (Just try it.)

Only when many ideas have grown, should the builder be prepared to refine the final design from a distillation of all variations on each theme. By this time, the eraser should be well worn.
Plan the design process well, and always be open to lateral thinking and always take time to understand the whole process to place your ideas in context.

The main engine mounts can be one type, or a mixture of various types. As mentioned earlier, the main engine mounting type is fixed, where engine vibrations are transferred fully into the frame. Metal frames are often heavy enough to absorb and dampen many of the more dangerous vibrations.
Lightweight motorcycle frames are more likely to be a problem. There must be consideration to position a rigid engine in the frame in such a way as to minimise damage. It is possible to spread the load more evenly over the frame by employing different wall thickness tubing, spreader plates and gently tapering or smoothly filleted bracketry.
Making the engine as part of the frame is common. Making the engine as the frame with just rear and/or front extensions is a way of eliminating many problems as well as reducing weight. Both should be considered. The road legal JP4a frame weighed just three pounds and was two foot long. See also the Norton Cosworth and BM1150 motorcycles.

Flexible engine mountings are usually rubber, where the rubber absorbs the high frequencies, then gradually transferring more of the lower frequencies to the frame. Tuning the rubber mountings is beneficial in a metal frame, but even more so in lightweight frames. Can be very effective if designed well. Always design flexible mounts to apply the force of gravity, acceleration and deceleration to minimal disadvantage.

For a comfortable, yet 'tight' chassis, then consider partially mounting the engine in rubber, just at the front, where the engine vibrations originate from piston/crank displacement. At the rear, where the engine should be tight with the swing arm, then this area can be less independent. Just enough rear mounting rubber between the swing arm pivot mounting and the engine to allow the engine to move at the crank area. This will tighten up a vibrating engine design with minimal looseness in the engine / frame interface.

For solidly mounted engines, upper engine mounts should be used where possible, but remember that they are mainly for keeping the upper frame rails from vibrating destructively with the lower engine/frame rails which have different masses and therefore different natural frequencies of vibration. Keeping the whole frame vibrating in harmony leads to less frame fracturing. Poor design here can also lead to frame fractures e.g. the early XR200.

Where wrap around frames are not bothered with the above, the upper engine mounts are often designed to allow the engine to be underslung, with just a little help from the crankcases to add a little triangulation support to the main beams to prevent 'sagging' under extreme loads. Therefore always study the engine mounts and the way they are positioned for both structural and vibrational effects on the whole machine. The engine will always dictate part of the frame design, so use it to best advantage.

Consider the alloy frames at the turn of the millennium and how they manage to get all the rear forces into a small, strong area round the rear swing arm. This leads to a strong, light and rigid box area from upon which the engine, swing arm and shock unit can be mounted. From this either a fixed or rubber mounted engine can be connected to the rest of the frame.
Modern frames follow a design path led by others. Examples of underslung engines include MZ and Seely Condor Norton. The large Cagiva off roader using the air-cooled Ducati engine is worthy of particular note, as it is supported from the rear yet suspended between the cylinders, free of it's duplex lower frame rails. Similar ideas may be gleaned from Bluell and others.
Other options include adaptation of some of the more obscure Greaves technology. This has been applied to advantage in many machines, and a few motorcycles.
Simple mounting points are common for production machines, but for custom builders, subtle and sophisticated arrangements can be used to advantage. Do not confuse sophisticated with complex.

Alternative design considerations.

Many other designers, mainly private manufacturers with low production runs have differing ideas, of which low centre of gravity often being considered the best in contrast to the ideas of the larger motorcycle manufacturers.
The pros and cons of the concept / theory / pub-talk, is fairly well discussed from universities to pubs, and for all the thought and words spoken on the subject, personal preference seems to be the final arbiter.

As can be seen in the picture, I have no problems with low centre of gravity machines at walking pace, but as this is a recumbent, I don't even have the luxury of being able to move my upper torso to help control balance. This is a JP3 machine and just one of a series which all handle wonderfully, far nicer than most other bikes I've ridden.
I actually prefer the 'recumbent' riding position for many hours. - the force needed by the engine is less and I suffer far less wind hassle. In an accident I am feet first. If I slide, I slide while riding on the bike for protection.
As all my test riders say - you've just gotta ride it to believe it. I have forced friends to ride, it, then had problems getting the bike back for others to test.
Note the single sided rear end and the 14 inch seat height, feet forward and underseat handlebars. This bike has knocked up many hours of seriously fast, yet relaxed riding in many countries.
Despite Ducatis, works Nortons, Yams Hondas and all the rest, this is still my favourite bike for Llanberis Pass and the Princetown to Ashburton road.

Many independent, open minded designers prefer a very low centre of gravity. The decision to choose conventional or low centre of gravity may well depend upon the terrain and roads prevalent in the intended purpose of the machine.
Twisty mountain roads are by far the best places for low centre of gravity machines, where slaloming and line chopping are great fun, highlighting the advantages to great effect.

For fast, straight line machines, a more conventional design may be preferred, but the stability for this, using low centre of gravity has shown no problems. Indeed, straight line stability with almost ZERO rake angle has been exceptional on machines such as the JP5a/b on rough roads with a sixteen inch seat height and hands off at over seventy miles per hour. I have ridden my JP5a/b and JP6b hands-off down steep hills with almost zero rake, yet handled absolutely superbly, with total control and feedback second to none as I overtook cars on the bends with no hands. Simply an incredible experience with superb handling. (The JP6a also had just the one shock absorber unit supporting both front and rear suspension.)

Front ends.

Unlike traditional forks, and as demonstrated by Tony Foale, almost zero rake is perfectly usable. Zero rake is mainly only applicable on hub centre steering designs, where the suspension and steering are independent systems, whereas forks need some rake to absorb heavy bumps more efficiently. This seemingly unimportance of rake highlights the importance of trail.

It is almost impossible to advise on rake and trail because all bikes are different. Although normal amounts of rake and trail from similar machines will often work well enough, they are not always ideal for all weights and sizes of riders and their riding styles. When building a custom machine, start with a ball park rake and trail, based upon the similar machines such as custom, touring, sport or whatever, then be prepared to adjust the rake and trail during testing to get the best handling bike for your particular riding styles.
The easiest adjustment is trail as the top yoke can be adjusted with a slotted central bolt hole and suitable shims or strong adjustment bolts to allow the trail to be adjusted. I always consider this as a good development tool for traditional forks, as it allows the sensitivity and stability of the machine to be adjusted for most, general purposes.

Rake angle (measured in degrees).
Rake is NOT the angle of the fork legs.
Rake is the angle of the steering head relative to the flat ground.
Rake is technically there to enable the forks to slide with minimal distortion when meeting a bump in the road. This is basically for the vector of the forward motion of the bike and the vertical force from the road bumps as needed for smooth action of telescopic forks.

The machine moves forward and the suspension must move vertically, so because they are sliding tubes, the forks are angled somewhere between these two conflicting needs. Take note that modern racers are getting lesser rake angles as the quality of roads and race circuits get smoother.

(Bikes such as the old Honda 50/90's and the chop in the picture, also have rake angle, but this is not always needed, as the supple leading link suspension arms do not need any rake angle for suspension needs. If Honda have thought about the C50/90, then it's mainly for cosmetic reasons to maintain a traditional look. It also ensures a good wheelbase, but allows the handlebars to be ergonomically placed closer to the rider then would be found with vertical steering system.)

Extreme rakes on chops still handle reasonably, but taking your hands off the bars is not always possible, at any speed.
These extended forks on a friends chop, have good handling because the trail is well sorted and the leading axle suspension works as intended, and although not a large suspension movement, what is available is well controlled and works in a supple manner. It also has a nice amount of genuine anti dive on the brake linkage.

With sensible rake angles, then hands free riding is possible, right up to near vertical angles as proven by Tony Foale with a motorcycle whose forks were set to pivot almost vertically. The JP4, 5 and 7 have been test ridden with zero rake angles.
The rake angle of some JP series can be adjusted while riding :)

Trail.
(Castor in the USA) (Measured horizontally in inches or mm)
Stability and trail are interconnected, but not guaranteed, despite the number of 'calculators' available, as they do not guarantee stability. Tyre pattern, profile, pressures, the stiffness or sloppiness of the steering head bearings, and a host of variables including rake and fork choices will still make this a black art.
If in doubt, start with what the nearest commercial machine has ! then prepare to modify during testing.
There are no set rules to rake and trail in the real world for a machine to get the best possible handling, so constant development always pays dividends in this black art.
Making telescopic and leading link forks with adjustable rake and trail is discussed later.
Hub centre steering often has adjustable rake and trail.

Back to the drawing.
If using forks at the front and the weight distribution is decided, then lay the forks in profile on the paper. Position the front axle, then adjust the forks for the same steering angle as the generic bike for which they are designed, or modify as required. Telescopic forks must be angled so they slide easily under influences of road surface irregularities acting horizontally from the front and the load of the machine acting vertically such as hitting a kerb, and also the load acting under gravity and when braking.
Excessive fork angles such as chops cause flexing vertically, while steeply mounted forks may cause flexing horizontally. For a starting point, consider checking the rake and trail of a selection of other similar machines so that normal road forces acting on the forks are in a manner that minimises side loading on the tubes as they slide.

This is merely a starting point for the design, although other forms of front ends are possible. If building a radical machine, standard forks will allow the testing of the main frame and other components without building a radical front end until the main components are sorted.
It is often the amount of trail that will refine the handling. This can be tested by offsetting the axle on the fork legs, but is difficult to do. Where a forged steel bottom yoke is used, they can often accept a small amount of distortion, allowing a selection of top yokes to adjust the amount of trail. A small amount of adjustment in the top yoke makes a large difference in trail. Where a top yoke with the central hole slotted and adjusted with front and rear bolts, then minor experiments with the amount of trail will be much easier. Never use modified test components for long term use if they are dangerously stressed.

If deciding to build different forks or even a radical front end with any of the many forms of suspension, then allow extra room to cover the options at this stage in the design.
If the reader has previously built or ridden a machine which handles well, then it's dimensions such as rake and trail can be applied as seen fit in the light of experience. Do not expect the same front geometry to work on all machines, as the influences are legion. Always take into account the differences between the various machines, including weight, centre of gravity, power, tyres and many other variables.

From the front wheel and the forks with the chosen rake and trail can now be drawn on the paper.
Mark in the approximate steering head position on the drawing if the wheelbase has been roughly decided by the various engine and rider weight distributions. The front end will be optimised during the build process.

Wheelbase.

Trials bikes have a short wheelbase, to negotiate tight corners with high ground clearance, whereas a drag racer needs little ground clearance to reduce looping. Conventional bikes need ground clearance but this is normally small on modern roads, or unless the engine is wide and prone to excellent cornering, where the engine must be raised to ensure it does not scrape. therefore the wheelbase need not be dependant upon any particular factor, but based mostly upon weight distribution and stability.
A short wheelbase bike with high centre of gravity is more prone to diving under braking, unless it has genuine anti dive geometry, so a little extra wheelbase may help.
A long wheelbase bike will be a problem in congested cities or where the ground clearance may become inadequate.

The front wheel position can be decided to a finer level later in the design and building processes, once the rear wheel position is decided, usually in accordance with engine parameters, plus the weight of the rider is known and the point at which the rider and engine weight acts. (as measured earlier, and decided later in this monograph).

For many machines it is preferable to work forwards from the rear wheel, often due to the constraints of the final drive and the fact that most weight is on the rear. Also solo / dual rider weight distribution calculations or approximate judgements are easier.
For racing, the best wheelbase may be the starting point to optimise handling around the rider ergonomics and aerodynamics.
Few designers will start with the front wheel, which can often be positioned later for best balance vs wheelbase after the major items are arranged according to normal engineering constraints.

As the basic weight balance has been decided earlier, the choices should be fairly easy due to the ballpark or finalised weight distribution. If building a fairly conventional machine, such as a basic commuter with two identical wheels and wish for some reason, to have approximately even loading on both wheels, then measure the balance point of the combined rider and engine. Then position the wheels equidistant from this combined balance point.

As the rider and engine weight are by far the heaviest items by a vast margin, and the frame and suspension weight is often equally distributed across both axles, then the desired proportional loadings will be very close without considering the chassis weight. This assumes the frame and suspension weight is equally distributed between each axle, although radical machines may vary this aspect. Only those who carry heavy loads at one end, such as when touring may wish to refine further.
Never aim to have more weight on the front wheel than the rear in normal use unless braking.

For machines which use different wheel sizes, the loads which the designer prefers to place on them should be proportional to their tyre sizes. (Not to be confused with diameter.)
It is important to choose the tyre for the purpose. Normally the ideal tyre size will be decided by riding machines with similar set-ups.
Where new or unorthodox designs are being considered, the foot print of the tyre will depend upon the tyre pressure and its load. A long tyre footprint from a narrow, large diameter tyre may make slow speed turning harder, whereas a rounder footprint from a small diameter, fat tyre can make turning easier.
Foot prints can usually be found by locking the rear wheel either by brake or wedging the tyre against the swing arm, lifting the wheel, rubbing with dirt and lowering carefully onto a sheet of paper, then loading to normal conditions. Do not roll the wheel. This is very basic, and tyre choices is a subject in its own right, but worth considering at a general level while choosing generic tyre profiles and sizes, and just as important, the desired tyre pressures.
At a professional level the tyre is placed on a sheet of toughened, lightly oiled glass to check its foot print.
The foot print of the tyres where cornering will change and can modify the overall handling, so choosing suitable tyres can always improve or reduce the handling of a bike in a minor manner, and is only noticeable when on the limits while racing at the ragged edges (and just beyond) of the bikes envelope.

The rear tyre is usually chosen first, to match the requirements of the engine output and the riding parameters. Then the front to be a suitable match to the rear tyre. For many, the cross section of the tyre is most important, as it defines much of the way the leaning when cornering will behave, also the weight offset as the machine leans and any squirelling/tyre stability relative to the road at high angles of lean.
The matching of front and rear tyre cross sections and tread patterns being very important for balance and all round handling.
Suitable consideration of load and power transfer is important. Where the rear tyre is larger, more contact patch on the ground to transfer high power is possible, or with a lighter front wheel to assist easier steering at low speeds, but still maintain enough weight on the tyre to maintain safe braking and cornering forces. An infinite amount of refinement in this area should be expected, recognised and developed in light of experience from building and riding.
The centre of gravity of rider and engine can be ideally positioned to assist this refinement as the design develops during test riding. It is for this reason the front and read wheel diameters and aspect ratios often matches the general front to rear weight distribution, and the footprint to match the use of the tyre.
Be prepared to redesign, modify and experiment in this area, especially under extended testing conditions.

If making a radical machine, decide on a general optimisation of the rider ergonomics, as radical machines often suffer early control problems. Alternate controls and secondary ideas should only be added after the fundamental design has proven to work.

When positioning the rider and engine such that the ideal weight distribution is applied, remember the superb effects created by Mr Cooper when he positioned the F1 engine behind the driver. When developing radical machines, the builder must seriously reconsider all possibilities, then use this to minimise problems from the basic design parameters.

Final transmission.

There is a vast range of sprockets available, so choose the best range for the front sprocket, which is the most difficult to modify as it is often engine specific and there is limited clearance. Then choose the best gearing match of rear sprocket for that chain size relative to the rear wheel, desired speed and acceleration profile. From this the rear cush drive can be built to fit the rear sprocket mounting.
For any custom machine, always choose the most common sprocket design to maintain spares availability. This also usually gives a wider choice of teeth.

If front (and rear) sprockets must be modified, as they occasionally are, get them built by experts and keep them close to the original diameters, so the forces on the gearbox output shaft bearing is not excessively compromised.
Although there is a vast array of commercially available sprockets and bearings, keeping the design to integrate original or generic components, will enable the owner to find replacements more easily and ensure a life long supply of spares.
If the extra offset permits, then larger sprockets can be welded to standard sprockets, but any offset force must be taken into account. It is always best to machine an old sprocket on a lathe to take the newer sprocket, then weld accurately for a safer design.
Where non standard components are used, always make or buy a spare.

Gearing may limit the diameters of the rear wheel.
Most commercial aftermarket suppliers offer a suitably wide range of sprockets for most engines. Some suppliers have a catalogue with the dimensions and bolting patterns, so politely ask for an old copy or the chance to photocopy. If sprocket details are not so easily available, simply work out what is the ideal and start looking.
Working out the gearing can be done simply by keeping to the original engine sprocket, then adjusting the rear sprocket number of teeth to match the new rear wheel. For example, if changing from a 17 inch rear wheel to a 16, then measure the overall diameter of the outside of the tyre of each wheel. It is the rolling diameter of the tyre that is important, not the rim size. The outside diameter of the old wheel divided by the dia of the new will give a number such as 1.2 or 0.8, in this example, 1.06. (17/16=1.06)
If the original rear sprocket had 42 teeth, then the new rear sprocket will need less teeth because the rear wheel has a smaller diameter, so 42/1.06 = 39.62 or 40 teeth is the nearest. If racing, then 40 is closest. - But if commuting or touring, then uneven number of teeth will spread the wear more evenly, especially if the front sprocket unfortunately also has an even number of teeth.
If changing from a 12 inch wheel to an 18 inch, the figures work to give a proportionally larger rear sprocket.
Gearing numbers are only a starting point, as the new machine may have less aerodynamic drag, allowing it to go faster so that the original sprocket may not be ideal. There are many variables which may only be decided on the road.

Most rear sprockets will require a cush drive to prevent undue wear on the drive train and wheel mountings. Such shocks come from accelerating, engine braking, poor road surfaces and a host of other influences.
A rubber mounted engine is not effective as a cush drive due to it's mass, although it can take some generalised shocks from accelerating and engine braking forces.
The rear cush drive may range from using original manufacturers components and mounting to a standard wheel hub, to building a special axle and hub set.
Where a special axle is built, then the simplest cush drive is to fit rubber bushes on extended sprocket mounting bolts, and upon these bolts fit rubber bush tubes which can be welded to the drive flange. A simple example such as Honda C90 rear swing arm bushes, then making tubes to hold them securely and welding the assembly to the axle unit. See also XL185. When making cush drives, always make sure the centre of the rear sprocket will pivot upon a well greased central alignment bush to prevent undue misalignment. This bush should be built oversize and then machined accurately to allow the sprocket to run true. (See alternatives to lathes later.)

If the engine is to be rubber mounted, then the flexing must be accommodated by mounts which maintain the swing arm relative to the engine sprocket under all loads, especially during acceleration.
A rubber mounted engine can rarely act as a partial cush drive device, as the mass of a heavy engine will prevent much high frequency absorption of movement and not prevent stresses on the engine sprocket bearing and other transmission components. The cush drive should always work in the low mass items of the sprockets, so the rubber can be allowed to do its work.

There are many other aspects of transmission.
(For example with the JP7, where I included reverse gear, using an electric motor which engaged to the engine sprocket when the neutral light or clutch switch allowed it. This worked reasonably well, and as I used a concentric swing arm, the chain was always at the correct tension, thus I could engage first gear, pull in the clutch and press the starter motor button (which turned to the reverse button when the engine was running), to allow me to do fast three and four point turns.
The JP8 takes a different design of final transmission, where the unusual chassis allows the chain to always be in the correct amount of play and with no need for a rear axle adjustment, and the rear brake on the engine sprocket shaft, then the rear end is completely devoid of anything but the suspension arm and the rear axle and sprocket for a very clean design with minimal unpsrung mass, which should complement the handling character of the rest of the machine.
So always think beyond transmission as merely a chain or shaft.)

On both the side and top views, temporarily sketch in the best position for the top chain run, allowing for the differences in sprocket diameters and movement of the swing arm.

An end view of the machine should now be drawn on lining paper, copying the dimensions from the other sheets to create the various chain run, foot pedal widths and seat base. Draw in the lowest position of the footrests to decide upon ground clearances, from which a line for minimum cornering clearance can be constructed. Allow for a partially compressed suspension, or if racing, an almost fully compressed suspension, as cornering forces at maximum lean can be quite high.

The drawing now offers a rough layout of the machine. There may still be no fully defined frame as yet, just the ideal positions of the rider with essential components as required for the design. The reader will be sorely tempted to start sketching in a final frame at this stage.

The lack of drawings in this monograph should now be showing a positive response. The reader will have a set of full size sketches with their own way of designing a machine.

Draw in the frame lightly if so wished, but for some designers, there is far to go.

The builder may not know for certain the geometrical effects of the proposed design, possibly leading to poor handling. Hub centre steering which allows adjustment of rake and trail can be very useful for completely unknown designs but can be difficult to design and build, and comes complete with it's own set of problems and advantages. See later monographs.
It is not possible to offer advice for all machines, but starting with conventional rakes and trails for similar machines will often suffice. (Hubcentre steering builders have a more open and happier field of opportunity in this area. See HCS, later.)

Suspension.

For the builder, suspension is the second line of defence against long term road shock problems on the chassis, engine and rider. Tyres being the first.
Consider carefully the ground upon which your machine is to travel, as many modern roads are rather good, but the occasional one may need you to have a reasonable level of extra travel, unless you are prepared to recognise problems early and slow down accordingly.

Always consider the suspension structurally, as a means of reducing the forces on the chassis and use the suspension not only to conform to road irregularities but also as a means to lighten the structure. This should then help to keep weight low and may in turn reduce the requirements of the suspension.

The swing arm will want to pivot from a natural point, which, in many cases is approximately level with the wheel suspension movement at half travel. This will give a line which may often find a naturally close position to the engine mountings for the pivot point. The closer, the less effect from lift or squat under power, depending upon whether the pivot is above or below the sprocket axis. For most machines which rarely suffer full compression, this may be reduced to a line between the engine sprocket, swing arm spindle and rear wheel axle at one third compression. In some special cases, the position can be used to a specific advantage such as on trials machines, where controlling squat from quick start can be particularly advantageous, to make the bike perkier.

Where the rear swing arm pivot is close to the engine, the swing arm may be able to pivot concentrically with the engine sprocket for zero drive play and zero problems. Alternately it can be simply mounted on a close bracket on the rear engine mounts, or through suitable swing arm pivot built in or onto the engine itself. When viewed from the side, the rear swing arm spindle mounting should always be positioned as close as possible to the engine sprocket, ensuring the minimal distance between engine sprocket and swing arm pivot. This will reduce the amount of play required in the chain during swing arm movement and minimise any bad effects of chain tension acting on the suspension.
For best results use a concentric design, where the swing arm pivot and the engine sprocket are concentric. See Mead and Tomkinson 'Nessie'.

Poor positioning of the engine sprocket above or below, relative to the swing arm pivot can induce rise or dive under acceleration, and to a lesser degree a similar if negligible effect under engine braking. Always position for a neutral effect across the whole of the ride envelope unless otherwise required.

Mounting the swing arm on the gearbox/engine as per Honda Firestorm and Norton Commando can often lead to a chassis which does not actually connect to the swing arm, but is mounted remotely as part of the engine assembly. This can offer some engine isolation from the rider and yet maintain perfect swing arm to engine sprocket alignment. A flexible chassis/swing arm interface does not always handle badly if designed well.

For very tight handling, try to avoid any rubber mounting in the chassis structure between front and rear axles. Zero rubber mounting between the chassis and suspension arms can lead to a slightly harsher, tighter ride with better handling and feedback. See also Ferrari F series and formula one cars. - The rubber shock mounts are a separate and different case which do not affect chassis and suspension alignment.

If the front pivots of the swing arm are widely spaced, the alignment will be retained more easily. This is another advantage of having a wide swing arm, pivoting concentric with the engine sprocket, such as 'Nessie', JP7/8 and a few others.

The photo shows a Bultaco Sherco trials bike, one of my favourite machines from both design point of view and also as an incredibly fun machine to ride in all conditions, often on just the rear wheel.
Riding trials is one of the best ways for keeping fit and a sharp mind and reactions.
This is an extreme example of minimalist yet incredibly robust design, which allows the machine to literally dance about on its rear wheel, while under full control. Note the rear suspension, engine mount and rider footrests are optimised very compactly, (an extremely narrow machine) and close to the centre of gravity.
Consider this example from two viewpoints: One, as an engineer, where the compactness of the rear suspension is phenomenal, where most of the forces are resolved fairly closely around the swing arm pivot area. Secondly, as a rider, where total ability for the machine to be manipulated over almost any obstacle is made possible by the rider, while applying just the rider load through the foot rests, but allow the rest of the bike to leap about under full control from the riders hands and feet.

Whether a trials bike or full blown touring machine, the swing arm area is always of paramount importance.

Suspension pivot points will depend upon the wheelbase. Excessive swing arm length is not always a problem if the engine needs to be more forward. A long swing arm may simply need more rigidity which is often much lighter than the extra frame structure or bracketry of a shorter swing arm. The main problem with long swing arms is suitable suspension mounting which must reduce excessive bending or twisting, especially on single sided designs.

The standard dual sided swing arm can be built from components closely following standard practice, but designed to spread the loads for a rigid structure. When translated into steel, this usually means box section tubing, with a tall, thin section, tapering towards the pivots.
The tall section supports the weight of the bike and the vertical suspension forces, whereas the thin section shows that the solo motorcycle takes very little in sideways forces, unless it's a single sided design with a powerful engine.
Widely spaced long swing arms, such as wrap around concentric designs can be surprisingly rigid. Triangulation again. Braced swing arms are often original designs with extra tubing to reduce flexing. They can also be designed better from the outset, without need for external tubing or bracing if clean lines are required. See also 1999 Aprilia 125 road racers.

Single sided rear swing arms have problems of axle mounting and the attendant larger eccentric housing often employed for chain adjustment. The split eccentric housing is a very common design, but a potentially weak area which must be carefully designed for maintaining strength while keeping the unsprung mass as low as possible for good road profile compliance. There are at least three other ways to overcome this problem. The JP8 series is testing some options and I may be able to offer advice in a later monograph.

When designing conventional rear swing arms, the use of two small, semi-unconnected swing arms may allow the wheel to distort relative to the frame. Therefore ensure that the complete swing arm assembly is sufficiently rigid in all planes and torsionally to minimise problems. The normal suspension forces will be exaggerated by driving forces of the chain or shaft, or some other drive methods.
The forces on the rear axle come from the central force of the tyre contact, the wheel bearings, and the offsetting chain and sprocket. The rear brake, which may act in compression strut or tension rod or direct into the swing arm.
Maximising the wheel spindle design with wide supports at its ends can also help reduce distorting forces, if suitable bearings permit. Braced swing arms are commonly applicable for handling higher loads.
Trials bikes have the advantage of short swing arms and a need for compact lightness, which opens up a vast range of opportunities.
Motocross may still retain metal swing arms unless carbon becomes fashionable, whereupon motocross will soon sort out the good from the bad composite designs. Road bikes will then follow, integrating carbon swing arms - in the same manner that alloy swing arms were tested in the public field prior to all-alloy frames. Only recycling requirements may foil this path.

Consider using the space around the wheel to give a wide, well-spread load area. Shallow angles cause unnecessary higher loadings. The three nodes of rear axle, front pivot and shock mount should be a well spaced triangle. Draw in the tension and compression areas on the drawing then modify the design accordingly. If using a simple constant section beam for the swing arms, then ensure it can take the load without bending. A large thin wall tube may cause crumpling, especially if the suspension is not mounted near the axle. Always try to use a large tube for strength and maximum torsion resistance, but which can also clear the chain run. Box section is best in many cases. There may well be high levels of compression and tension, especially on single shock designs.
If the suspension unit is not on the centre line, there may also be high torsional forces to overcome, which should be avoided wherever possible, or taken into account by good design.

Once the pivot point of the rear swing arm is decided, the most natural compression point for a shock unit can be decided.
If using simple shock units without amplified movement linkages, then make an arc from the bottom shock mount, then sweep an arc from this point centres on the swing arm pivot. The ordinary shock should ideally lie along this line.
The closer the shock gets to the swing arm pivot, the heavier the load placed upon it.
At the wheel end it takes a standard load and is essentially vertical. At mid point on the swing arm it must resolve twice the load and acts at an angle closer to the smaller diameter arc and therefore only needs half the movement, but twice the spring load and twice the damping.

If like me, you often have to building using whatever shocks are available or using unknown shocks, possibly because they are high spec scraps or you have rebuilt them or are just available for pennies, then go carefully. First decide the load to be applied at the rear of the bike over the rear axle, then measure the load on the shock per unit displacement. - Put the shock on a block of wood, on bathroom scales and compress it about a quarter, then three quarters of the way. Make a note of the readings. If a single shock design, then make a direct relation between the shock load and the load expected on the bike when stationary and a single rider. This is measured earlier with the expected loads of the engine and rider, plus the load of the expected frame weight. A rough guess will usually get ball park figures. This can be adjusted during final placement of the shock on the frame. If dual shock design, double the readings of the shock. If the shocks has five position spring compression, set it to the second lightest, the upper three are for heavier loads. If the spring is mounted on a threaded adjuster, then keep it as it is, unless you know the previous owner has messed about with the settings, whereupon you should search out the genuine workshop manual for the machine and adjust it to the makers settings, after measuring for any sack in the spring.
If the bathroom scales are too weak, then apply half the force though the shock by employing a plank on the scales, pivoted with the shock half way.
Now make a rough guess of the overall rear axle loading of the basic machine and decide the position of the shock relative to this. A strong shock spring may be far from the rear axle, while a light weight spring may need the shock to be closer to the rear axle to take the load, and with commensurably lower amount of movement. The final position will be refined during manufacture of the machine, but knowing whereabouts the shock(s) will need to be on the drawing is always important.

Many modern suspension systems use a rising rate suspension system to enable a constant spring rate and shock damping rate unit to act with a geometrically increasing spring and damping rate. This allows a supple movement over the initial movement, to follow gentle undulations and any minor bumps, but at the full travel end of the shock units movement, the force applied is far greater, to give a firm ride and damping characteristics. Such an adaptable suspension is essentially a simple spring and damper unit, but at the expense of a few intermediate links and attendant pivots.
This rising rate concept is not available on forks and simple shock units, which must use variable wound springs and tapered damping nozzles or other methods to make the best of the relatively simple internals. Rising rate is easily adapted for use with hub centre steering systems.

A more basic variation on this rising rate system is to use a simple damper and spring unit, but angle it so that it only offers a small proportion of the force at initial movements, but the final movement is employing maximum force by being perpendicular to the swing arm pivot movement for maximum resistance to movement at full stoke.

It is common to fit a spherical point in the lower end of rising rate shock mountings, especially on dirt bikes, but a strong rubber bush top and bottom will allow any sideways play to be resolved without undue reliability problems.

Due to the movement of the shock closer to the swing arm pivot the shock is at an angle, so the shock moves in a reasonably linear way. As it is only the bottom of the shock which moves, then only this moving portion need be considered relative to the arc drawn from the swing arm pivot. If the shock deviates from this idealised arc then the forces will be less and be relative to the amount of deviation. This involves simple trigonometry which most bikers do not enjoy. So an approximate guess will suffice for designing, just make sure the shock lies approximately along the curve drawn from the swing arm pivot. The final position will be refined when fitting the actual shock to the actual rolling chassis.

The shock mounting point can often be incorporated optimally into the frame at an early stage in the design process and should be considered in conjunction with the rider forces acting upon the seat, as the rider is a considerable part of the weight. The suspension unit(s) mounting and positioning can range from vertically compressed to almost horizontally compressed depending upon the design and type of swing arm and linkages.
Always bear in mind the overall purpose of the swing arm, from the short rear swing arm as on trials machines, to the long swing arm.

Shock movement ratios must be properly checked, as they can vary from 1:1 to almost 4:1 on modern mono shock units. Check the position and the loading of the proposed unit in it's original machine, then position appropriately. Shocks working at high ratios with or without intermediate linkages need strong mountings.

Most good shocks can have a wide range of replacement springs and adjustment. Most damper fluids can be mixed to dial in the overall damping parameters, but try to keep close to the original fluid viscosities to match the standard spring forces, and reduce any damage to orifice washers.
The advantage of a steel frame is that the shock mounts can be rearranged after testing without too much difficulty, even if the upper cross beam to which it is mounted has to be moved. Always tack weld and initially test the load curve, modify until close, then partially weld and test fully after initial test rides. Finally refine using the adjustably of the shock unit during later road testing.
For early tests during the assembly process, the rider should be able to sit on the basic chassis, whereupon the shock unit should compress about ten percent of it's movement. (Dirt bikes up to fifteen percent.) Adjust the position and / or angles until this is achieved rather than the shock parameters. Simple positioning using climbing tape and rubber sheets to prevent slipping can often work surprisingly well to keep a shock in place during early tests. If this is not possible, simply tack weld until satisfactory. Where the frame is still in paper form, use planks of wood to load a simulated test rig to check the angles and positions for the loading required of any unusual design.

Front suspension - forks.
For the front end suspension, telescopic forks can be built but rarely worth the effort.

If intending to research, modify or advance telescopic design, either go in slow incremental steps or take a set of giant leaps in many directions. Then choose the best aspects to merge into a truly better machine, but only if the advances prove applicable.
Forks may seem to have reached their design limits. But anything which advances or improves the future of forks is always welcome, as forks are an integral part of bike design as seen by the general public. Consider the Yamaha hub centre design and its lack of public acceptance.

Building forks is best left to aftermarket copiers, where the basic design can be copied and low friction sliders can be built to take suitable tubes and bushes from commercial suppliers or simply machined on a lathe where needed.

Therefore the front end sing telescopic forks is a case of having to use the closest option to what is desired. As this monograph tries to offer solutions, not limitations, hub centre steering is also considered.

Following along the lines of the BM telelver system is a mid way solution, which is far easier to build than many forks systems and also allows some geometric anti dive while retaining good, adaptable rake and trail.

For those not happy with present fork design, consider adaptable damping valves controlled by electronics. This will allow supple movement, but an acceleration (deceleration) and brake pressure sensors used to stiffen the damping under braking. The options are wide and the electronics is not overly difficult. Start with a simple solenoid to block part of the damping when applying the front brake, which can be actuated via the front brake light switch. Another sensor to measure road irregularities may also be used to adapt constant velocity damping over short time spans to give adaptive suspension according to the general road undulations over set periods of micro seconds to many seconds.
It is surprising the Japanese have not added adaptive suspension to motorcycles even though cars have had this for years and forks can always improve from such technology.
Even some mountain bikes have this technology !

The better opportunities for front ends may be in the direction expounded by many such as Difazio and refined by ELF in their 24hour racers. Such hubcentre designs offer so many advantages that makes other front ends pale into insignificance as it removes these problems. I now build most of my road machines with HCS, as the results are hard to fault.

HCS often employs a single sided front swing arm. Although single sided suspension is theoretically wrong, it is still employed in many superb machines. Where applied on special or radical machines, it is ridden and enjoyed much more than most conventional riders could ever imagine.
For such swing arms, either large thin wall tubing or a swing arm built up from pre-formed sheets is most common. The selection of rectangular tubing popularly available is wide and should supply the needs of most builders. Round section is also possible, but less efficient at resolving such forces. If high torque is expected, then tubular designs may be preferable. Most designers prefer box section, but heavily triangulated in plan form at the front of the rear wheel to minimise torsion problems, and often taking advantage of the widely spaced, swing arm design which pivots concentric with any front sprocket of a 2WD system.

(Shocks need not be just simple designs. The JP6 had one shock, (not unlike the Citroen 2CV,) which was compressed from both ends, from both the front and rear suspensions, using differential lever system which was adjustable in the field. It also needed a secondary centring system and did not work as well as expected, even though the initial concept was to keep the machine level on rough ground, where the front bump would translate to a rear end push, and vice versa to keep a more level and supple ride. It worked, but was not a great success. I used a Suzuki monoshock. It had a remote reservoir, so the shock could be mounted horizontally between the front and rear single sided swing arms and allowed the damping oil to be free of air bubbles. The bike was road legal and tested at high speeds on the very twisty fast roads between Tavistock and Callington, and between Princetown and Moretonhampstead. The concept has promise but the JP8 has moved the basic concept on much further and with greater subtlety.)

Seating.

Spare parts.

Steering head bearings.
The taper roller is the definitive head race, as it takes all loads well and with excellent spread of the heavy load imposed by the front end while still allowing minimal friction. No contest.
For hub centre designs, the steering head pivot design is open to all comers, but if ball races are used, they should be deep groove or preferably angular contact types. Spherical steering bearings as used on car steering linkages are usually too tight from new and have no adjustment.
All motorcycle steering bearings must exhibit zero friction with zero play.

Swing arm bearings.
These are either silentbloc rubber bushes, plastic bushes, or metal needle rollers.
Balls are not recommended, nor are large rollers, because swing arms only pivot over a few degrees, so the point loading of the bearing is far too localised to ensure long life, where notching will eventually ensue. Although taper rollers are used on shaft drive machines and applicable on other motorcycles, needle rollers are smaller and lighter, which spread the load wider and roll through larger displacements for better wear.
On shaft drives, the taper roller is used to ensure correct alignment of the shaft to the engine and must be retained.

Needle rollers cannot take side loads, so either side load bushes or some other form of side load resolution should be accommodated. This is usually a metal or nylon side thrust washer, which need not be complex, as the side forces on a motorcycle are light, unless used for sidecar work. Consider INA NX series of needle rollers with side load ball races as a good starting point for clean designs.
Depending upon the design, the bearing on one side of the bike may take most of the load during cornering, so the side loads must be resolved to best advantage.
On many commercial motorcycles, needle rollers suffer from corrosion, so good sealing and regular lubrication must be considered for long term reliability. Grease nipples are simple to fit and should be considered for retro fitting after the final tests, strip and checks of a good chassis. Steam engines use grease nipples and last for centuries.

Understand well what is required of the chassis mounts.
For the rear power transmission, a strong, well controlled assembly is necessary, especially on powerful machines, where metal bearings are often required between engine and rear wheel to prevent misalignment from an asymmetric drive train. The usual choices are rubber for commuters, plastic for mid sized machines, and needle rollers for mid to large machines. For ease of compatibility, standard motorcycle components can be used in various ways and allow easy spares availability. The alignment of the front wheel relative to this rear assembly will be decided upon the amount of accuracy for the purpose of the machine. Never be afraid to slightly overbuild the swing arm bearings, as the extra weight will give chassis rigidity where needed and tighter handling with long term reliability.

Suspension bearings.
Even on a 'tight' chassis with metal suspension bearings, there is no need to use metal bushes to mount shock absorbers. Because the shock absorber is itself a flexible medium, the rubber simply refines the set-up and reduces shocks into the frame.
Where linked suspension with intermediate links are used, then the needle roller is a good set-up, with the occasional spherical bush joint where flexing may misalign the shock shaft, otherwise causing it to fracture. Correctly aligned suspension in rubber bushes is a pretty robust design, which allows for a little distortion as often found in manufacture.

Assessing the general design.

If you can make a real frame, you can make a wire model. It doesn't have to be accurate, just use solder and straightened paperclips. With a soldering iron and some wire, build a rough model of your frame and then load it to see where it breaks. Do not just see which wires bend, but also the direction that they bend. Model the engine and suspension with wire load points, so you can see what the engine mounts are going to do. Modify and try various designs until feeling confident. Load and twist it in many ways so it breaks. An evening spent like this tells you loads (pun intended) about your design. Design it many times, so you need only build the real thing just once. Good bikes are built with the brain, not thrown together in the back garden. If you make three different wire frames, comparative tests can be used using standard weights such as increasing numbers of bags of sugar balancing precariously on matchboxes for spot loadings.
Never confuse poor soldering with poor design, so double check.
If a bike takes six months to build, an evening testing the design is always time well spent.
If making box s section tubing chassis or swing arm, then model it in cardboard to see how it distorts, highlighting the probable failure, crumple or weak points.

While designing, try not to get caught thinking or sketching the machine while at work. It happens. As the design grows, ask people whose opinions are trusted, they may well point out obvious problems. Make notes.

Despite all the best intentions and input from others, decide on the final form while remembering the old joke: A camel is a horse designed by committee. So always aim for the purest form of the intended machine, and suffer compromises only when absolutely necessary.

Hopefully, enough has been mentioned to highlight the areas of concern and to encourage the development of ideas beyond mere copying of conventional machines. Designing is often a state of mind and occasionally a wonderful insight, requiring new or unusual skills to be developed and tested. This may need new designs and skills in light of building up a range of skills, lateral thinking, experience, testing and 20/20 hindsight.
Unfortunately for beginners, good hindsight requires many years of investment.

Thought: Unfortunately, the design will have problem areas. When these become difficult to solve, understand all the problem areas and leave it alone for a while. Leave the design for a few days or weeks so ideas can form, settle and refine. There is much debate about where good ideas come from, the answer is often difficult to define. What can be said, is that they do not come from staring at a drawing for hours.
A long, gentle walk along a beach, forest or upper moorland helps the mind to relax, where ideas can flow freely. Never try to force ideas. They must be allowed to flow freely. They may even come while standing in a queue while shopping. It is times when one is not directly involved with design that good ideas freely associate between the neurones. Always carry a notebook and a couple of pencils, or, like many good thinkers, desperately regret not doing so.

With all the above and much of the following text in mind, the frame design can be finalised.

Preferably after three or more weeks of designing have elapsed, the reader may start building the frame.

Never skip the three weeks of 'just thinking' before building, It is surprising how often beginners and experts alike spot the obvious flaw or a simpler way to make a more effective design. Designing an easier or more reliable way to build an machine is an art in it's own right and should always be cultivated.

New stock steel tubing is surprisingly cheap and so are simple hand held angle grinders. Make life easy for yourself.

Safety and supplies.
Goggles, a dust filter mask and ear protectors are even cheaper and will pay the highest dividends in the long run, while also reducing hospital visits now and in later life. There is no point building a bike if you cannot ride it. Safety goggles, breathing mask and ear defenders are NOT negotiable, cost little and can be bought at the same time as the metal and welding rods.
1/8 th inch, 3.2mm welding rods will suffice for main welding with a basic arc welder, with a selection of smaller rods for thinner metal.
Small gas mig welders are now easily available at low prices, the author has picked up a second hand one for forty pounds, which needed some minor work. Always buy the common type, as there one probably only one or two mass producers of such items. This way, spares are easy to get.
If buying a new mig welder, NEVER buy the 'gasless' type.
Always price up the cost of spares and consider getting a new swan neck inner lining tube, which often seems to wear out first. Never coil up the swan neck unless absolutely needed. Always position the welder where it can be easily used, or taken to the working area.
On mig (metal inert gas), the shield gas which replaces the flux on the conventional stick welder is usually carbon dioxide. Look out for low capacity and the more economical, larger capacity CO2 cylinders which look identical. Usually 360 grammes vs 600 grammes. Always shut off the gas valve after use.
The other advantage of mig welders is that they can be converted to weld aluminium at minimal cost. Always preheat aluminium before welding. See welding later.
Get safety equipment the same time as the tubing and welding rods, plus the grinding and cutting discs for the angle grinder. Discs are available in various diameters, so choose the correct ones. Thin discs are for cutting, thicker ones for general grinding. Make sure the discs are for metal.

When fixing a nail or hook in the wall for the angle grinder, hang the ear defenders, goggles and mask on the grinder, so they are always ready for use. You need eyes to ride a bike.

General frame building.

Never be afraid to discard a poor first try when building a frame, as the cost of tubing is minimal compared to the time and effort involved. Getting it right from the start ensures a much better machine. The first tubes to be built are the most important, so go for gold from the outset. If the first attempt at a main frame tube is less than perfect, then remove and refine, or simply make another and use it's remains for smaller cross tubes and other secondary items.

Decide how the frame will handle the loads and forces, then choose your tubing accordingly. Look at tubing used on bikes, trikes and cars to get a feel of the sizes needed. Find out the wall thickness of the tubing used, for this is just as important as the outside dimensions. If in doubt, always use stronger tubing. You may be able to afford a lighter seat lug to break, but not a structural part of the frame. A few extra pounds or kilos on the main frame tubes are always good insurance.
If you dislike metal work, use square tubing, it's easier to fit. Round tubing needs a lot of profiling work to join properly. -
The Lamborghini Countach has a tubular chassis which is made up of a large number of small round tubes arranged to make many triangles, called a space frame. The triangle is the most rigid shape around. If you don't want to bend tubes, then try designing a frame from many big and small triangles. The later Lamborghini Diablo used square tubing for it's space frame, was easier to build than the Countach, and was stiffer and lighter.

Do not have long unsupported tubes. Always employ smaller tubes to stop the long main tubes from flexing or bending. The whole frame can be made from large and smaller triangles. A rectangle can distort, so guess what you should do. Some motorcycle trellis frames use a similar method.

The picture shows the JP2 trellis space frame. This design folds in half so the whole bike can fit into a suitcase. The two wheels align on the same axis when folded so it can be easily pulled along on the road wheels like a golfing trolley. The fuel tank is QD, the batteries nicad and oil tank self sealing like a non spill inkwell.
Yes, it's for a six foot tall rider and is road legal.
This frame uses extremely thin wall tubing and bronze welded throughout and was just a few pounds in weight. It is totally indestructible even when a 16 stone rider slid it sideways many times for an hour during rather fun testing, plus some minor motocross jumps. The two stroke oil in the frame showed no leaks after a few years. The 12 volt electronic ignition was retained, but the 12 volt lighting and horn were changed to 6 volts to reduce the need for extra batteries. (The Sub-C nicad batteries were also inserted into the frame tubes. See also electrics monograph on my website.)

An angle grinder with cutting and grinding discs is a must.
Make sure you use ordinary steel, and use seamless tubing if you can. Iron is never used and stay clear of fancy steels unless fully competent. Don't try saving money by buying cheap tubing for the main structural parts of the fame, and stay clear of wrought iron.
When built, you will be loading the frame to see where it flexes, so expect to add some more tubing, fillet plates and/or gussets as required later.
Make a rough guess of the sizes of tubing you will need, but prepare to change them slightly when confronted with the metal stockists options.
As this is subjective analysis of a machine which needs not only strength, but also style and proportion, even in the frame tubes. Make an ideal sized cardboard tube (round, square or rectangular) for assessing the frame tube sizes in relation to the other components laid out on the bench or in the garden on boxes, then find the nearest match in steel. Make the card tube as long as possible, so it can lie along the arranged components to help gauge the general look of the frame tubes relative to the engine and wheels.

Grab your drawings, the cardboard tube used for sizing, metal tape measure and a pencil, then find the local metal merchant and see what they have to offer, and ask their advice. The best way of deciding is often simply looking and deciding what seems best. - 'I'll have two lengths of that heavy tubing, four of that smaller square tubing and a sheet of that'.

This is not at all scientific. -
There are no calculations and no structural analysis. If in doubt, use similar machines as a reference point. Do not put yourself down, even a poor mechanic has a working knowledge of what has been used in similar circumstances. Your main assessments are comparative to similar structures plus a safety margin. The ability to use the eyes in conjunction with common sense is a very powerful tool.
To work out the actual sizes using maths needs a lot of work, the understanding of loading in structures, vectors, forces, welding areas and quality, and then testing. For most people, common sense and a good sense of proportion is more than adequate.
For those of a cynical nature or old hat engineers who have seen it all before, - 'Statistics in the hands of an engineer, are like a lamp post to a drunk, - used more in support than illumination.' (A.E.Houseman.)

If in doubt, look for similar successful engineering equivalents. If in doubt, ask friends. If in doubt, build stronger than expected. If in doubt, be cautious and try it anyway, you will often be pleasantly surprised during early testing. Doubt is a positive attribute, it can also be a safe one.
If in the worst case, the frame fails during initial testing, then you will need to strengthen, or even rebuild parts with stronger tubing, simply returning to the start in the light of experience before too much expensive work is done. Initial testing is always done on the basic rolling chassis, so that in the worst case, the whole basic frame can be affordably discarded and a better frame made, before all the fiddly, time consuming work is done to turn it into a work of art.

You may be surprised by the vast selection of tubing available and it is always in a variety of wall thicknesses. Always measure the tubing on equivalent machines for comparison. Don't expect much British steel in Britain - it's often from Eastern Europe, Portugal or Turkey.
Circular, square and rectangular tubing, strip and rod. Make yourself a shopping list and be prepared to have it cut for a small fee, as it usually comes in twenty foot lengths which the supplier can cut to what ever length you need. Measure three times, cut once, or do they deliver?
There will also be alloy sheet, wire mesh and a host of other stuff. Don't forget to buy the welding rods and grinding and cutting discs at the same time. And to repeat, goggles, ear defenders and breathing mask too. A lightweight pair of leather welding gloves is useful when handling hot metal.
If in doubt, ask for a photocopy of their materials list and retire to a local cafe to think, or return next week.

When carrying long tubes in a car, always take newspaper or rags to cover the seats as the tubes are often covered in preserving oil which stains easily. Take plenty of cloth to wipe off excess preservative. Most bike frame tubes can be cut overlength and still fit in a car if stuck into the passenger foot well, and the tail gate open with a warning red flag attached. The passenger seat may need to be removed, so take a few spanners. Take bungees to keep the tail gate from bouncing around.

When the tubing meets the bike bits, it may be decided that it is not the right size. At this stage, a rethink will be a lot better and the original tubing will become stock for other work, such as to align the wheels to the floor lines, or perhaps gateposts and drains, or an engine hoist.
Therefore just get the main tubing first, and if in doubt or on a tight budget, simply get one length, then return for more as needed. Practice bending and welding on the first choice of tubes and when competent, get the perfect tubing later.

To repeat, if worried about wall thickness, go safe. A few extra pounds in the main frame is weight well spent. You can be less cautious for non structural parts such as seat bases, battery box mounting brackets etc.

Practice welding until your welds are consistently good. - Full penetration without excessive heating, and smooth, with no encrustation's and no undue distortion. Practice, practice, practice. See welding later.

Types of steel. - For most frame purposes, just use mild steel.

TYPES OF STEELS.

DEAD MILD or low Carbon. 0.07 to 0.15 percent carbon.
Available as Black and bright bars. tubes, wire.
Pipes, chains, rivets, screws, nails, wire. boiler plates.
Easily worked when hot, but difficult to machine owing to tendency to tear.

MILD. 0.15 to 0.25 percent carbon.
Available as Black bar sections and sheet Bright bar strip and tubing Forgings.
Ship plates and forgings, gears, shafts, nuts, bolts, washers, rivets, chains.
Easily machined and welded, and is cheapest steel.
Ideal for bike frames. Welds easily. Availabe in many sizes shapes and wall thicknesses. Preserably non seam welded tubing, but seam welded tubing is perfectly good too.

MEDIUM CARBON. 0.25 to 0.5percent carbon.
Available as Black bar, sheet, sections and plate Bright bar. rods, flats and strip Forgings.
Machine parts and forgings. castings. springs, drop hammer dies.
Responds to heat treatment and can be machined satisfactorily.

HIGH CARBON. 0.5 to 0.7 percent carbon.
Available as Black bar and stripSilver steel rod.
Hammers, sledges. stamping and pressing dies. drop-forging dies, screwdrivers hammers, set-screws

HIGH CARBON. 0.7 to 0.8 percent carbon.
Punches, cold chisels, hammers, shear blades, drop-forging dies, lathe centres. spanners, band saws, rivet sets (not rivets). vice jaws.

HIGH CARBON. 0.8 to 1.0 percent carbon.
Punches, rivets, sets, screwing dies, screwing laps, shear blades. drop-forging dies, saws, hammers, cold chisels, springs, axes, rock drills, milling cutlers, lathe centres, reamers. See also my knife monograph.

HIGH CARBON. 1 to 1.5 percent carbon.
Drills, milling cutters, lathe tools, files, wire drawing dies, hacksaw blades, ball bearings, screwing dies and taps.

ALLOYING ELEMENTS.

CHROMIUM Up to 1.5 percent. Used with nickel and / or molybdenum increases hardness and allows high UTS with considerable ductility

COBALT. 5 to 10 percent. Retention of hardness at elevated temperatures.
COBALT. 12 to 18 percent. Increased corrosion resistance in stainless steel.
COBALT. up to 40 percent. Improves coercive force in magnet steels.

NICKEL. 1.5 to percent. Increases tensile strength and toughness.
NICKEL. Over 20 percent. Used in corrosion- and heat-resisting steels.

TUNGSTEN varies. Strengthens steels at normal and high temperatures.

MOLYBDENUM varies. Used in stainless steels to provide resistance to sulphuric and other acids.

VANADIUM varies. Increases hardensbility.

NIOMUM. TANTALUM. TITANIUM. All three prevent weld decay in chromium steels and in nickel stainless steels.

BORON 0.003 percent. Great increase in hardenability.

COPPER 0.2 to 1.0 percent. Increases corrosion resistance.

It is assumed this text and any other research material has been read and understood and at this stage the basic design is fully refined. Frame building should be surprisingly straight forward as you will know what it is that you are intending to create. You should have thought it though many, many times.

You do NOT need accurate drawings.
Even though I trained as a mechanical designer and draughtsman, I never use very accurate drawings: Drawing are to get the general frame design sorted before building process begins.
The true art of frame accuracy comes from the building process and subsequent refinements.

Clean all parts, engine, tubing, then practice and set up the welder. Make as many test welds as needed before committing to the frame building. If it takes a few weeks to become competent at welding, then so be it, or find a friend or local firm who can competently weld.

Have safety equipment at hand, and ensure plenty of room.
Check the fire extinguisher is acceptable, preferably carbon dioxide. At least have a bucket of water which must never be used on high voltage electric items.
A hand garden spray gun filled with water prevents localised overheating and puts out minor flames.

Make frame building a positive experience.

When everything is prepared, frame building can, and should be fun.

Do not use the water to cool welded components unless absolutely necessary. Cooling hot metal will cause hardening, fractures and will weaken the structure.

The next step is to understand the materials to help understand the processes and general nature of the materials.
This is best done by building the components which 'cannot' change and then design the frame to support them. These have been discussed earlier and the most useful choice should be made.

Steering head. (Test piece.)

For those who are new to frame building, here is a test piece to start your apprenticeship and an engineer.

(In a once great Britain, engineering is a dying art. An engineer is one who understands the physics underlying processes and then design the machine to fit the job, then test it works as designed. A mechanic is one who can repair, but not necessarily understand the underlying processes. A modern day fitter is one who simply replaces. - An old style, apprenticed fitter is one who can file to half a thou and fit items by hand from basic materials and do so with stunning accuracy - and also be a forensic analyst with oily hands.
Ideally you should be an old style fitter with your hands, and an engineer with your mind.)

At this stage, an initial test piece can be considered, giving enough of a challenge to need more than one attempt to become an acceptable piece engineering. The first attempt will help the reader get to know the materials and the skills needed, while the second attempt brings forth the early stages in improving skills, subtlety and knowledge, plus it gives an item to compare with.
A steering head offers many skills, including accurate alignment, snug fitting bearings, and a rotating item which can be tested for accuracy, smooth rotation and a few classic pitfalls to learn at an early stage.

If not wanting to build the steering head, then use an item from a scrapped machine or have it made professionally. Invest in a decent item using larger taper roller bearings available from any bearing shop, or choose the often cheaper yet equally suitable bearings are available as aftermarket motorcycle items, which often use excellent large taper bearings at sensible prices and availability. For very large motorcycles, consider a the taper rollers from a car wheel hub bearing set. These are often much cheaper than buying separate items and are much more commonly available. They may also include oil seals and grease.

Think like an engineer: Keeping to standard components from other sources, means keeping it cheap and keeping it reliable. If the taper rollers are different sizes, simply buy two sets, or put the larger bearing at the bottom of the steering head, as this takes the main load. When used as wheel bearings, the larger one is closer to the wheel centreline to take the larger load.

If intending to make a steering head, get tubing equal or stronger than the original, and get everything perfect.
Reassemble accurately using old bearings, so you can weld it without damage. Then be prepared to replace with new bearings after welding if damaged through excess heat.

To align the steering head during assembly, the central spindle is needed. This may well be the original from a donor bike or an axle assembly or to make your own using tubing if a similar diameter.

The central spindle is usually a large wall thickness tube, machined to fit tightly into the bearing inner races. As the spindle need only fit the bearings where they are positioned, the rest of the spindle can be slightly reduced in diameter to allow the bearings slide more easily into position. Only where the bearings will fit, will the spindle need to be a snug interference fit, needing the bearings to be lightly pressed into position. Therefore a tube of slightly smaller diameter can be used, and the bearing areas built up with weld and machined or filed to fit. Where grinding down the shaft to fit the bearings is a problem, simply grind down the areas that the bearings are not going to fit first, then slide the spindle on a bar. Then apply the grinder to the bearing areas at an angle, which will cause the spindle to rotate as it is ground to size, allowing a gradual reduction of the diameter with a fairly accurate bearing fit. Start the grind at one end, to create a very fine taper, so the bearing is gently forced onto its final contact area, leaving highlights which can be gradually reduced for a perfect fit. A simple alternative to a lathe can be built using blocks of wood, an electric drill and concentric end pieces. The work piece is free to rotate, with the grinder applying the rotating force. This allows the spindle to spin while being ground to size. This may seem extra work, but is often much quicker than taking it to a specialist machinist. Who says you need a lathe ?

The simplest steering head bearing housing is a large tube with a close fit for taper roller bearing outer race. This tube can then be carefully smoothed away inside to accept the bearings firmly. Alternatively use a split tube slightly smaller and spread it firmly over the bearings, then tack weld the gap.
Or use a larger tube and grind down the slot to clamp gently with hose clips to fit the bearings. If using new bearings, fit the tube over the bearings and tack weld, then remove the bearings before welding. Tack welding will not give enough heat into the bearings to damage them, but ensure reasonable accuracy of fit. Full welding will damage the bearings.
The final tube should fully support the taper roller at each end and must be perfectly parallel, and axially concentric. If the bearings are a slightly loose fit, remove the bearings and simply swage (hammer the outside of the tube) to reduce the diameter by a few thousandths of an inch. Do this evenly while rotating the tube, to ensure the tube remains circular.
As this tubing is thicker than most, it may be necessary to weld the slot from both inside and outside to ensure full penetration of the weld.
After the outer tube is made, make an inner spacer tube to fit snugly in the main tube. This is often a slotted tube which can be pushed into position with a little spring force.
Use a lathe to turn the ends before slotting, so they are perfectly set at right angles to the tube. Alternatively use a set square, file and a practised eye.
Before welding in place, many very large holes or slots are then made in this inner tube so that it can be securely welded inside the main tube without damaging the carefully profiled ends. Slotting can be done using an angle grinder.
When accurate, assemble with the bearings and fully seat the bearings in position using the central spindle to ensure all runs firmly but freely. Then remove the spindle and inner bearings, leaving the outer bearings to maintain accuracy while tack welding the inner alignment tube.
Then remove the outer bearings, weld fully and clean.
Always ensure the inner steel bearing spacer tube has a strong enough shoulder to retain the force applied by the large forces applied by the bike on the bearing. If a narrow wall inner tube, it is necessary to grind two small undercuts for each bearing in the tube shoulders to allow a metal drift to be hammered against the underside face of the bearing so the bearings can be removed.
The welding of the inner tube must be strong, as it takes the whole weight of the front of the machine. If bottom yokes are close to the steering head outer tube, then internal weld failure will not be catastrophic, as the bottom yoke should be designed to collapse only a few millimetres until resting on the steering head tube.
Where internal welding is difficult, such as using a MIG rather then a stick welder, then slots can be made in the outer tube, to weld the inner spacer securely in place.

Careful design of main components should be fail-safe wherever possible. A small gap also allows for a simple O ring seal or a thin nylon seal or a lightly compressed closed cell foam seal to retain the grease. Closed cell foam makes a good seal, often used for camping mats and the softer, rubber backed mouse mats and swimmers wet-suits.

Securing it all together will need a threaded adjuster to apply just enough pressure on the taper rollers so they will turn freely, yet have no play. If machining a thread on the tube is difficult, then most designs will allow a central bolt to be welded on the upper end with a spacer tube and dual nuts or nyloc nuts to be employed for security.

The final tube should fully support the taper rollers at each end and must be perfectly parallel, and axially concentric.

When assembled on the central spindle, the outer can be allowed to spin and be dressed with an angle grinder. This will smooth up the ends and allow the outer surface to be lightly profiled and smoothed, while giving the bearings a chance to spin and settle down. After machining, fully clean then lightly oil or place in a plastic bag to prevent corrosion until needed.

At this stage, the assembly should be carefully inspected by a competent engineer. Look for the following: Absolute freedom to rotate, with minimal noise and no friction or intermittent stiffness. Gradual tightening of the assembly to remove slackness from poor manufacture will show up any imperfections, and the attendant lack of smoothness will need to be assessed, then eliminated on the second attempt. In most cases, the bearings will not be perfectly aligned as with a lathed item, but with careful filing of the bearing seatings of the inner spacer, little slop will be found. Prior to assembly, put a little marker such as a china clay pencil or lipstick on the bearing seating areas, and on the shaft. After assembly and snug fitting then rotating, the assembly can be taken apart and inspected. Look for poor seating of the bearings, especially where the main load will be applied. Ensure the load is applied across 80 percent of the load bearing areas. If it rotates badly, then strip and scrupulously clean before re-assembly. Then decide if you would you trust your life to this item.

If alloy slab yokes are not suitable, perhaps for easy modification of an early design needing trail modifications, then the yokes can be built up from flat, round and rectangular tubing. Again clamp split tubing around the main tubes and weld to make accurate clamps for the fork legs. Always employ double clamp bolts on each side, to reduce chances of failure. Lightly clamp over the fork legs and rotate the legs to see where the high points are, then fit carefully by reducing the high points with a scraper or half round file. Finish off with a flap wheel in an electric drill so that each fork leg will be securely held, as this is where half the weight of the bike is supported. (More than half when braking hard or stoppies).

The bottom yoke should take all the load, with the upper yoke often used merely to prevent flexing and to support the handlebars. See some 70's German Boxer top yokes which are made from thin alloy sheet.
The trail is directly controlled by the difference in angle between steering spindle and the fork leg alignment, or by offset of the spindle on the fork legs. Many machines have the fork legs and yokes parallel for easy machining of the yokes, but minor adjustment of the upper yoke can drastically adjust the amount of trail and may be used to advantage. When using steel bottom yokes, the degree of angular difference between spindle and fork legs can be readjusted slightly and maintained by an adjustable upper yoke. Make the top yoke with a slotted central spindle hole, then use tight fitting split sleeves either side of the spindle, with bolts to adjust the fore and aft position to adjust the amount of trail. Never use development devices for long term use unless absolutely safe.

Many small engineering firms can build steering heads, as it is basic engineering. Take the bearings along and get the spindle made at the same time. Likewise, many engineering firms will make slab yokes. Slab yokes are usually machined as matched pairs, so accuracy is not too important, and the split clamps can adjust for a little inaccuracy. Preferably demand accuracy to a thousandth of an inch, so any alloy split clamps are not put under unnecessary strain. Ideally the fork tubes should be a slight interference fit before machining the slot. Always ensure the central holes are a snug fit on the central spindle.
If making your own yokes and no offset is required, then drill the central holes first, using a smaller hole, then fit a clamping bolt to hold them together. The fork tube hole is machined on one side only, through both slabs clamped together. Then swap a yoke over on the bolt, so they act as guide for the other fork leg holes to ensure absolute symmetry.
Always ask around first, as there is often someone in engineering who can make a set at work during the night shift. On a recent V12 efi trike project, the yokes were 2 inch thick alloy slabs and CNC machined.

The steering head should have given enough skills to develop small scale welding , both tack and fully welding in awkward areas and accurate cutting and filing of tubes. This will allow basic frame building, once symmetric assembly has been developed.

Alignment.

When making frame and suspension components, always try to build them as mirror pairs before assembling the frame. This applies not only to front forks but to all symmetrical pairs of components, frame rails, and right through to the rear swing arms and seat rails.

By making components as matched pairs, the whole machine is more likely to flex symmetrically. This will reduce overall distortion and help maintain wheels and frame in line for better handling, particularly on lightweight machines.

As mirror pairs, simple alignment jigs can be used to advantage for accuracy.
Fit the suspension components to the jigged parts such as hub fittings and ensure they work as required. Tweak, adjust and modify before building the frame. Once in position, the secondary frame components can then be made to fit them.

The frame should be made to fit the perfectly aligned suspension, not the other way around !
The suspension is the active component, the frame merely there to keep it all together in a rigid manner. If you were to make the suspension to fit the frame, the machine will be more likely to end up with uneven sides and poorer handling.
Done properly either way, it may indeed make very little difference, but if aiming to build a machine towards perfection, always consider what exactly you are building, the relative structural hierarchy of the components and how they should be assembled for best effect.

Understand the hierarchy of the structure:
The engine powers the tyres. The tyres transfer forces to the machine and the steering controls the direction. Therefore the wheels are the prime concern, with the suspension used to keep the wheels in an ideal state under all conditions.
The frame is there to keep the suspension in the right place, so it can do it's work properly and accurately.
The engine and riders, although not structurally important, also sit in or on the frame, as it is a very convenient way to accommodate them.
Therefore if suspension is to be custom made, it should be made to fit the perfectly aligned wheels. The frame then made to fit the perfectly aligned suspension.

Swing arms.
Basic swing arm manufacturing consists of a flat base sheet as an alignment table, with a set of matched V blocks to take the fore and aft spindles. The swing arm spindle and wheel axles can then be perfectly aligned horizontally and adjusted to align as require.
Then the tubing and bearing mounts built up as needed.

It is preferable to leave the shock absorber mountings until later, as the spring rates are best assessed on the assembled structure. See also above and later.

For building and aligning smaller components and sub assemblies such as swing arms, use thick compressed fibre wood sheet as a perfectly flat engineering surface. Medium density fibre MDF, despite its bad reputation, is acceptable but must be thick enough to prevent distortion.
During welding, the reference surface will become damaged, so a light cleaning with a flat edge to remove welding spatter and a very light rub down with fine sand paper on a flat block may be needed before the next process to prevent inaccuracies appearing. Keep it clean to keep it accurate.
Where V blocks are not available, then use identical sizes of wood to support the spindles and use a good set-square. If building the swing arm directly on the engine, then also mount the engine on the bench as part of the jig before any assembly.

A simple wooden jig can be used for positioning during the welding process. The jig must be accurate and possibly use concentric cones sliding snugly over steel rods for alignment. This allows the components to float on the rods, yet still have the tubes aligned by tapping or screwing the cones into place. An alternative is to use close fitting tubes to slide into the frame components. Always rotate alignment rods prior to use to check they are not bent.

Centre lines should be drawn and drilling jig holes accurately marked and drilled. The centre line can be drilled with a sequence of holes, possibly using drilling plates or metal shelving strips as an accurate drilling jig. From this, dowels will allow drilling plates to position symmetrical alignment holes by flipping the plates over for perfect alignment.

Cheap Vee blocks can be made from the same MDF material, and when made from one piece then cut into four pieces, can allow perfect dimension control. Four identical Vee blocks are ideal for aligning swing arms, as the two axles are then perfectly aligned relative to the horizontal plane of the base plate.
Maintaining perfect linear accuracy between front and rear axles and other components can be simply controlled by aligning with the centre line and using large flanged nuts on a long stud bar as a linear comparator for each side. (Much more accurate than an eye and ruler.) Using two comparators will allow them to rest on the axles during welding for perfect alignment.
When accurate, accidental movement can ruin all the preparation, so if needed, little dabs of wax on the blocks onto the base with a soldering iron and candle wax can hold all securely and will show up any failure of position if accidentally knocked. Do not allow the welding heat to burn the MDF.

Where the engine is also to be mounted on such a jig, perhaps to build a wrap around swing arm, the base material must be suitably thick to support the weight, and vee blocks will need to be quite tall, so always ensure they have relatively large feet. The engine can then be carefully positioned with wedges, which allow gradual adjustment for perfect positioning prior to fitting the frame tubes. If using through bolts on the engine, fit them if possible, to help align the engine to the swing arm.

Always remember that the engine is aligned subordinately to the rear wheel by the chain or shaft alignment, and that the rear wheel controls the engine alignment by the sprocket positions. Likewise, if making custom hubs and rear sprocket carriers, then the rear sprocket position is always subordinate to the wheel alignment and tyre profile and clearance.
There is a natural hierarchy from the rear wheel to the rear sprocket and thus to the engine and the rest of the machine.

As can be seen, a small table top of accurate flat wood will hold the engine and rear axle in the desired and accurate position, allowing a swing arm and a frame to be built up on the aligned assembly.

Making a frame.

Clean a flat and level floor or work bench.
If working on a less than perfectly level floor, but it will be imperative to keep the spirit level correctly aligned. Therefore mark one end of the spirit level so it will always be aligned pointing to the right and the front of the floor. If this is not done, a less than accurate bubble alignment will soon be followed by a less than accurate machine.

When aligning wheel housings, swing arms and forks to engines and frames, then jigging of the whole rolling chassis can be done between two large, straight planks. This holds the wheel rims and thus the suspension accurately, while the engine can then be supported and positioned upon these planks. When the main frame tubes are fitted and tweaked into perfect alignment, the frame can then be assembled in the knowledge that the main components are correctly aligned.
Wire wheel building is described in 'A builders Guide to Motorcycle Mechanics, Intermediate', available on this website. Steel sheet and aero wheel building is described in 'A builders Guide to Trike design', also available on this website.

To prevent the wheel assembly falling over, use cross planks under the main planks and to lift the main beams off the ground so they are high enough to support the engine on wooden wedges or blocks. Ensure there is plenty of clearance for the frame and suspension components to be fitted.
The suspension swing arm and forks should naturally align after fitting to perfectly aligned wheels.
If the bike is very long or planks are unavailable, then long straight lines can be made on the ground using a chalk string, pulled tight and flicked vertically to leave a straight chalk line. Then apply masking tape either side and paint the centre line. See also lasers later.
It is assumed the tyres are partially deflated so the planks clamp directly on the sides of the more accurate rims. The tyres should be of identical size and type, or symmetrical compensation strips used for the thinner width of a front wheel rim.
For best effects, the wheels should be supported as high as possible on the rim to offer maximum accuracy. This may require offset pieces to clear any wheel width differences, wheel dishing, or frame obstructions.
Ensure the tops of the wheels are also in line as well as the bottom of the wheels. Before clamping, ensure they are accurate by mounting just the wheels and checking. It is assumed the wheels are trued accurately and the wheel bearings are perfect.
After clamping lightly, make micro adjustments to refine the way the wheels are mounted, and when accurate, fully tighten and double check. Planks can be held together with may methods such as sash cramps, through bolts or rubber bands made from old inner tubes.

Most commercial frame jigs support the components merely by the swing arm mounts, axles and steering head bearings. These are often less accurate, as the finer inaccuracies cannot be so easily seen and remedied as with complete wheels. The latter may be better for mass production, where a fully refined design can get away with such compound levels of imperfection. Only swing arm pivots may be compromised using the twin plank method, if the wheels are not perfectly vertical with each other, but if the swing arm is jig built, and as the swing arm only moves through a small arc, such misalignment is often negligible.

Perfect fore to aft accuracy between front and rear axles and other components such as main engine mounting bolts can be simply controlled with large flanged nuts on a long stud bar as a comparator for each side.

There is no need to make up the front end of the frame at this stage. Leaving the front frame tubes a little longer than needed, will allow then to be dressed back for accurate fitting of the assembled front end before any steering head is welded in place.
If needed or desired, set up and check the front wheel steering angles, ground clearance and any other aspects of the design. Position the front end, usually the forks, with steering head and align with spirit level and plumbline, then block in position. If this is difficult, fit the handlebars on the forks with the headstock and rest them between two chairs, adjusting the handlebars to get correct, or simply hang from cord from the roof. It's not ideal, but as long as it's in the right place when you start welding the rest of the frame, this will do for now.

Use new engine mounts, or old ones ground out of the donor frame, cleaned and fitted to the engine. The engine should be aligned and double checked with the chain in place. The suspension will be blocked in place and accurately aligned. Double check that all mounting bushes, brackets, spindles and such like are in place.
Any complex gearchange should by now be well considered to understand where it can and more importantly, cannot fit. If in doubt about the gearchange path, possibly with an unusual design, use temporary dummy set-up or whatever is suitable to check the alignment path and action.

Using blocks and wedges, place the engine in position above the centreline with the right ground clearance. Use a spirit level, straight edge, plumbline and your eyes to make sure everything is aligned and level.
Align the engine relative to the rear swing arm and drive train.
Ensure the chain run is accurate, using a long straight edge parallel to the chain, usually using an engine reference surface such as a removed sprocket cover machined face. Whether a new or worn chain, position the chain adjusters appropriately. Then tension the chain by moving the engine relative to the rear wheel. This allows a new chain to fit with full adjustment available. It is better to buy an over length chain and split it for the best match to within one link of the desired wheel to engine position. Do not use the chain as a primary alignment device, always use a metal ruler or straight edge and check it across the face of the rear and front sprockets. The chain can then be used to align the engine's fore and aft position.
If the machine uses a propshaft rear end, and even if shortened or lengthened, it should be connected as intended by the manufacturer. It is important to have all drive splines in the correct position for the movement they permit and universal joints aligned correctly. Although many propshafts run in a rigid swing arm, there is nothing to prevent having a semi floating propshaft, so that the propshaft can transmit power to unusual rear ends. Such propshafts may need a sealed spline and the cush drive should preferably be within the engine, usually fitted as a spring and ramp on the gearbox output shaft.

It is possible to lengthen or shorten prop shafts and their swing arms. This is often a simple case of extension or reduction. Always be careful when modifying the drive shaft so that it balances perfectly and can carry the torque. A simple weld may not suffice, so an additional tubular sleeve may be required. Always balance a lengthened shaft prior to use, spinning it at high speeds between simple centres to check. Use an electric drill and an end spindle to assess vibration.
Lengthening the outside of the swing arm is straight forward, as most have their shocks mounted near the axle, so do not carry great forces. Where a single shock arrangement is employed, always take great care and more so if it is single sided.

Block the swing arms and such-like securely, then mark it all so you know when it's disturbed, - you don't want to line up perfectly to wrong positions. A dab of paint or nail varnish will do.
Measure using a metal tape measure. String or cloth tape measures can stretch too much.
Accuracy should be as high as possible, and certainly more accurate than most commercial motorcycles as defined by their workshop manuals. A few millimetres overall is acceptable. Try for zero error and don't take just one measurement, double check and triple check all the main parts.

An alternative to planks of wood and jigs are lasers, as they can supposedly offer a perfect centre line for good alignment while building. They are not as accurate as good planks, but they make a large machine easier to assemble. Cheap lasers are common. Key-ring lasers offer beams with the same basic property of expensive lasers; a single straight beam with a constant size. Cheap laser spots have marginal spot definition and diameter, but can give more accurate smaller spot by simply judging the centre of the spot, or using a keyhole plate a few inches from the laser to refine the spot. Don't make the hole too small, you don't want diffraction patterns.

Accuracy of alignment will not depend upon the laser spot quality, but on the mounting bracket, so most cheap lasers will do, the main consideration is the way the beam is used. Use of mirrors can distort readings as mounting for mirrors is often less than perfect and compound mirrors simply increase misalignment. Therefore it is better to eliminate such problems from the start and use the laser directly to provide the alignment path.
Two main methods. 1. A commercially purchased beam splitter, where the beam becomes a single plane across the whole of the chassis mounting area. This is ideal for overall alignment from a fixed laser unit.
2. A simple, cheap method is to mount the laser on a precision bearing and allow the laser to pivot and its beam to arc across the centre line of the work area. When the pivot is precision mounted on a spindle and lightly sprung, a simple cord can sweep the laser beam across the centre line of the bike. Light friction on the shaft and dual pull cords will allow the beam to travel and remain in a specific position on the work area, ensuring a component can be perfectly aligned to the centre line prior to fixing. Do not allow pulling of the cord to distort the mounting. Rigid mounting on a structural roof beam is ideal, as it allows most areas to be 'swept'. Old video tape recorder spindles and bearings are excellent for the purpose. If using a key ring laser, simply remove from its housing and connect a wire across the contacts, to a remote switch. The two separate wires to this switch can also be used to rotate the laser. This allows the beam to be switched on and swept across the machine to check and then be moved into position so the next component can be accurately positioned. As lasers and spindles are usually cylindrical bodies, then machining the mounts as one component will eliminate many inaccuracies, but connecting them by their internals makes for even greater accuracy.

At this stage all is ready to build the frame.
The wheels are perfectly aligned, swing arm pivots are accurately aligned to the rear axle, the engine, transmission and forks in position and aligned.

Always try to design a frame to employ full length tubes from the rear swing arm mountings through to the steering head for the strongest frames. The bottom frame tubes may also be capable of having the swing arm mountings welded directly to them.
Rob North frames for early Tridents were a classic example of the art.

Assembly methods.
There are many builders for who the above dual plank, laser or metal jig methods are too much trouble. For those who wish to prevent misalignment of a machine which is built in less accurate ways, such as simply welding bits as they are built, then there are two less accurate ways to build such frames.
These methods should also be applied to building a well jigged frame, to help further reduce misalignment.

There are two ways to quickly build a frame, front to back, or back to front.
Front to back means building the front end complete with steering head and mounting it to the engine mounts first, then aligning and building the rest from that. This can lead to gradual misalignment. Only suitable if the majority of the front of a standard frame is retained.
Back to front is safer, especially for designs using fork legs, because all the heavy work of building the engine and rear suspension is done first. There is then a solid design for mounting the steering head and front end which can be aligned to the rear wheel and basic frame assembly. This allows the builder to take time and fully tweak the front tubing after all the rear welding is done.

When measuring and fitting the main frame tubes for the steering head area, leave a little excess length at the front for the steering head area, which can be aligned and ground down to size later using the back to front method. The tubes which will hold the steering head can later be tweaked to ensure perfect alignment because, with the rear assemblies tack welded in position, they can be bent, teased and coerced into line for a perfectly accurate steering head relative to the rear wheel. When in line, the steering head mounting tubes can be ground back and profiled until a perfectly aligned front end is achieved.

Whatever methods you use, the welding must be good.

Preparation is the key to good welding, so weld a variety of test pieces and break them until absolutely right.
Unfortunately, many of the first welds are the main frame welds. If in doubt, tack weld and hand over to a professional. See welding later.
When making the full welds, always create them as symmetrical pairs, ensuring both left and right sides of the frame are evenly built up to prevent compounding distortion by welding just one side of the frame first.

For those building less than ideal circumstances, or who are not building in a jig, then they may wish to build the basic frame around the engine, then add the chain, rear wheel and swing arm, to make sure all is aligned by using a set square and tape measure. This is measured between the axle for equidistant measurements between rear wheel spindle, swing arm pivot spindle and a long cross bar mounted accurately in a front engine mounting hole near the front of the assembly. The check all is parallel when seen from the rear.
For those building in one of the many forms of jig or alignment devices, such as dual planks and wedges holding every component in position, then manufacture is much easier.

Start making the frame by aligning one main tube, bending if and where needed while off the jig.

If two main tubes, then make its mirror image at the same time. When the first tube is made, it is easier to make a mirror item when it's off the machine. This allows for ease of comparison and forming to shape without upsetting the rest of the structure.

The engine can be positioned on wood blocks laid on the two main planks, so all is kept together. Then adjusted into position with wedges which should be glued to prevent further movement once aligned. A few pencil marks across components will allow checking for potential problems should anything become nudged out of position.

Tube benders are available from hire shops, always prefer the hydraulic type as they can handle more gentle tweaking of the tubes for greater accuracy. Where cosmetic finish is important, gently clean or cover the bending formers to prevent unnecessary tube scratching. Polish the inner surfaces of the bender or cover with nylon cloth, or use protective sheets cut from high density polyethylene or similar, as cut from empty plastic engine oil containers. This is often important for award winning custom bike frames.
Tube benders can be modified with special additional brackets to bend box section tubing, but will often require applying many small bends along the tube to prevent creasing and thereby maintain strength.

A felt tip permanent marker pen is also priceless at this stage. It allows accurate marking of the centres of the curves for the bender, where to clean the metal for fitting the brackets and where to modify the engine mounts etc. A felt tip pen can also stir the tea, as this is a slow, steady process, not a rush, with plenty of looking and refining as the main components gradually take shape.

Where used, carefully remove the original engine mounts and trim them to fit the tubing. Then refit all major mounting brackets to the engine and other items. Align the main tubing on the engine mounts and to the swing arm with excess metal tubing sticking forward for the steering head.

In some cases, the rear engine mount may be a complex assembly or box section to take the engine mounts and the swing arm so they remain rigid to one another. If using a single rear shock and wanting to find an airbox, then any box section here can be incorporated into the tubing if it does not compromise the strength. If using a single backbone tube for an off road bike, then the carburettor air intake can be through the main tube, with an inlet in the main tube, up near the steering hear fillets, to give a good swamp proof intake.

The fitting of the smaller tubes such as cross braces between left and right hand side frame rails will need careful fitting, especially if using round tubing. So take your time and gradually grind or file the tubing to fit. The final placement of the secondary tubes will often be different from the drawing, as they will have a naturally better or stronger position as seen first hand, and is when an ordinary frame can become a good frame.

Build up the rear engine mounting area either from sheet, tubing or a mixture. Then bolt them gently on the engine. Temporarily fit any cross tubes to connect with the frame, but do not weld them until the main frame tubes are positioned, so they can be ground to fit perfectly later.
Repeat the process for each pair of tubes and build up the main frame components around the rear of the engine mounts, rear suspension and swing arm. Tack weld the main frame tubes just enough to hold them in position on the engine brackets and rear assembly, or whatever the design permits.

Occasionally, some frame parts will be obscured by outer components, so items such as frame mounting plate boxes may need to be built then fully welded prior to being ground down to fit the main frame tubes or other major obstructions.
On fairly conventional designs, do not fit the rear seat support rails or other minor components, as these should be fitted much later, after the main frame components are fully welded and tested.

Always design the components so they will fail safely. For example, if a shock mounting bolt or bracket should shear or it's bolt fall out, the shock should then push against a fame tube or bracket rather than be allowed to collapse further.

Double check the alignment of the wheels, engine and steering head / forks. As the forks and steering head are pivoted on the front axle, they can rotate around the accurately positioned front wheel, to gently rest against the protruding fame tubes to act a general guide of accuracy.

Gently tweak or adjust all main frame components as needed.
Use just the minimal amount of tack welding to get a perfect frame alignment. This will allow any imperfections to be repaired with minimal welding damage.
When accurately aligned, add more evenly spaced tack welds on each join to maintain alignment. Make a second check and tweak, break and / or adjust the tubes as needed.

Make three, well spaced tack welds on each join to maintain accuracy.

At this stage you should have the two or four main frame tubes or whatever design of frame, with the engine on blocks and swing arm neatly assembled and tack welded together on a large, perfectly flat wood-chip table top. The rear wheel may well be hanging off the side of the flat surface, blocked in the correct position.
The rear rim should align perfectly parallel to the side engine casing joint faces, while the rear sprocket aligns perfectly with the engine sprocket.
The tubes are held in place on the engine by tack welds and the whole is perfectly aligned and potentially strong, with neatly shaped joints prior to fitting any secondary fillet.

To repeat, the rear wheel rim defines the centre line of the machine.
Moving the rear wheel up and down the swing arm movement must not affect the alignment. otherwise the swing arm pivots will need to be rebuilt and re-aligned.
From the wheel the engine sprocket is aligned to the rear sprocket. The engine is then aligned to this rear assembly.

Because of the chain run, the engine may not lie neatly on the centre line and its weight imbalance may need to be offset by mounting the battery etc. at a later stage.
The rear wheel will also command the position of the front wheel. Therefore it is important to ensure the rear swing arm is accurately fitted to the rear wheel spindle without any inaccuracies and swings through its suspension movement with perfect accuracy.
The swing arm mountings are often thick steel plates or strong tubes through which the swing arm pivot bolt must align accurately with no play. All swing arm bolt holes are a snug fit to ensure the rear wheel remain in perfect alignment with the rest of the machine.

Good eyesight and a three foot long steel ruler is priceless, otherwise a suitable straightedge substitute is demanded, such as a one inch square section steel tube which can be laid against the rear sprocket and rear wheel rim to ensure excellent accuracy of the assembly.
The use of a stud bar with nuts to check the swing arm spindle and rear wheel spindle are parallel is recommended for total accuracy, especially if a single sided or shaft drive rear end.

The main tubes are often two or four long tubes with engine and suspension fittings mounted directly. In such cases, secondary tubes can now be positioned to support the main tubes. These keep the main tubes aligned and reduce flexing during side loads and jumping hump back bridges. Unlike main tubes which should maximise the most natural and strongest forces, secondary tubes can be lighter and fitted in a variety of positions to accomplish the frame needs. The classic support tube is from the rear of the upper frame to the bottom of the steering head, to triangulate the steering head area.
Make sure the engine can be removed. Avoid obstructing any maintenance paths. Classic problems include exhausts, radiator plumbing, rocker cover access, and also cylinder head and carb removal plus whole engine removal.

The non structural, minor tubing at the rear of the frame can be removable, leaving just the engine and suspension in position. This can be a good alternative for particularly awkward engine removal or maintenance and is common to many motorcycles, where the rear is bolted in place.

Do not mount passengers on removable sub frames unless the design is fail safe. Make sure any loosened bolts cannot not fall out, causing untold problems. If bolts can fall out, ensure the assembly will fail safe. Removable non structural sections should be fitted after the basic rolling chassis is finished. If making removable sub assembly seat support for maintenance of an awkward rear cylinder head, add a little extra wiring to the loom, so it can be swung out of the way with the minimum of fuss and easier maintenance and is ideal for complex V fours and big V twins.

It can be seen from such examples, that the refining of the design will continue throughout the whole process. Some of the minor refinements cannot be fully decided on paper, but often naturally evolve as the bike takes shape.
When welding, ordinary nuts are used on the engine and other mountings, but where nyloc or similar devices will later be used, welding often damages them, especially the nyloc types.

Triangulation between the tubes is will always make for stronger and more rigid frame.
A strong frame will hold everything together safely. A rigid frame will ensure the bits hold together without flexing. For best results, go for both. A heavier frame is not ideal, but more reliable, especially on early endeavours of this art.

For safety reasons, you can afford a little extra weight in the main frame areas.

Important note: At this stage in the proceedings, it is still possible to grind back and break the tack welds if needed to break and re-set any imperfect frame tubes. Be prepared to do so, as it will be increasingly more difficult to cure inaccuracies as the work progresses. Checking costs nothing, but is extremely important. Keep in mind what happened to the Hubble space telescope. If necessary, scrap whole sections that are not ideal, using the tubes for secondary components.

Where fillet plates are to be used, such as either side of the steering head, these should be left until after the main welds are finished.
Before the steering head is mounted, it is best to fully weld the rest of the frame, allowing any distortion in the frame from welding to be allowed before final alignment tweaking.

When completely satisfied, carefully build up extra tack welds until it is safe to remove the frame, then fully weld it.

Always leave the wheels and engine clamped in position on any planks or jig to act as a frame checking jig to check for distortion after welding.
The frame should be removed for major welding for many reasons. First, it makes it much easier for the welder to get positioned correctly for good welds, as this is very important. Secondly, it will show up any distortions and imperfections when replacing, allowing the builder to adjust or tweak the frame for good engine and suspension mounting. Third, it encourages the builder to add any little fillets and refinements, and also to add any little late changes and flourishes. Fourth, it allows the welds to be dressed for a smoother shape, thus reducing the chances of fracturing from any sharp stress points.
A clean profiled frame makes checking for fractures much easier during initial testing. Do not grind down the body of any protruding weld; simply profile gently.

DO NOT weld on just one side of the frame first, then the other side, as this can cause distortion. Weld both sides of the frame as pairs. For example, weld the left, then the right upper suspension mounts, then the left then the right rear engine mounts etc. Any distortion incurred by the welding will then be evened out. See welding later.
where applicable return the frame to the assembly jig to check for distortion.

Once the basic rear frame is complete, it should now be possible to temporarily fit the rear shock unit with tack welds just strong enough, then load it to check for the best position and action. As the front end and forks are not yet fitted, this can be done by supporting the front of the lower frame tubes or the engine.
With the shock temporarily fitted and the front of frame supported on blocks, bouncing up and down will also allow the frame to settle under the rear loads. Check axle loadings with normal rider(s). Adjust for about ten percent movement in the shocks with normal load on a standard, light setting.
Fitting a temporary bracket to support the front at the correct height , then loading the main part of the frame will stress the fame and swing arm, showing any inaccuracies from welding and / or asymmetric loadings on the frame. Noting these before fitting the front end will lead to a more accurate machine.

After full welding, check the engine and swing arm mountings to realign any inherent stresses. For those who wish to push the process to the fullest extent, have the frame and swing arm stressed by running the engine in the frame and swing arm, revving up and slamming on the rear brake to check for any distortion. Then apply the brake fully and watch for distortion in the frame and swing arm as the clutch is used (not fried) in first gear, against the rear brake.

Check the frame and then tweak, or grind out and reweld parts if distortion occurs.
When fully satisfied, double check the steering head tubing prior to fitting.

It is not necessary to finalise the position the rear shocks at this stage, just a few tack welds to allow the rear end to be fettled. Final shock positioning can be done once the front end and forks are fitted.

With most of the frame built and aligned, then the front end can be fitted. The steering head may be from a donor bike, or custom built, or like me, a front swing arm for HCS. Whatever you decide upon, then front end now has a perfect frame onto which to be aligned and fitted before welding in place.

The fitting of the steering head should always be done at leisure and with perfect accuracy.

When fitting the steering head last, allows the builder to get all the frame bits sorted first, the rear wheel and the engine and transmission correctly aligned and mounted.

Build up the steering head, the forks and yokes and front wheel ready for introduction to the rest of the machine. At this stage, the front and rear wheels need only be bare rims to improve accuracy.
The amount of trail bellow the axle to the line though the steering head will be different whether the assembly is done with or without correctly inflated tyres. For greatest trail accuracy, use tyres. for perfect wheel alignment, use bare rims.
For custom bikes with forks, I tend to use tyres and ensure rake and trail are as I demand, as they are nigh on as accurate as bare rims.

The welded frame and the assembled rear of the machine is blocked at the correct height on flat ground and aligned between two planks. the assembly is now checked for perfect vertical alignment with a straight edge on the rear wheel, so the front wheel will also align perfectly to this same spirit level setting.

The planks are clamped either side of the rear wheel, as this is the widest, with the front wheel placed between the planks. If no suitable long alignment planks are available, then use just one, and ensure to remember the difference between the front and rear tyre widths to ensure perfect alignment. If no plank, then use strsight metal tubes, or a tensioned piece of string or an industrial grate metal tape measure laid along the ground, all assistes iwith plenty of good eyesight.
With the wheels aligned, the whole front end, complete with forks and steering head can now be rotated about the axle for alignment and positioning to the frame until a perfect front frame tube profile is achieved.
Carefully grind down the steering head area for a perfect fit of the steering at the correct rake angle. If too much metal is removed, then the front wheel can be moved a little closer to the rear between the planks at the expense of a minimal change in wheelbase, without upsetting the rake angle.
If the frame tubes are a little low or high to fit the steering head, then simply raise or lower the front of the whole frame. As it pivots about the rear axle, it will often not appreciably change the overall alignment of the machine to any great extent.

Measure the identical distances from the ends of front and rear wheel axle points to position the steering head - perfectly central with the whole machine. Check the line running through the rear wheel centreline and through the front wheel and steering head. Check the vertical alignment of the front wheel relative to the rear wheel using the spirit level.

Now double check: Use your eye, a good spirit level, straight edges and a metal tape measure.

The steering head angle can be measured using specialist equipment, but a simple but large sheet of cardboard or plywood and a pencil and ruler, carefully divided up into a forty five degree angle by making a right angle from the base line, then subdividing it up further until down to 22.5, 11.25, 5.6, 2.8, 1.4 etc. using the appropriate subdivisions to make a protractor of the area in question. Use a piece of angle section bar with a straight profile to clamp on the steering head, so the angle can be checked and also the amount of trail.
A simple block under the front wheel should keep the steering in place against the shaped front end of the frame, held by resting the steering head accurately but with no inherent distortion.
(At this stage, if you have kids or misbehaved friends, keep them well away.)

It is not the fork leg angle that is important, but the steering head angle, as this decides the amount of trail.
Some fork yokes are such that the forks are not at the same angle as the steering head. Use the protractor to check for the preferred steering head angle.
Place an angled piece of channel bar against the side of the steering head, then look down this angle bar, to the projected point on the floor, and take note of the offset from the actual centreline of the steering head. Use a pencil to mark the position of the steering head axis on the ground. This point to the plumb line of the front wheel axis is the amount of trail.
Where the amount of trail is most important, as it is on most machines, then aim to get this the most accurate measurement of the front end. Ensure the rear suspension is tack welded, and that the machine sits on the ground correctly as if on the road. Then imagine a line though the steering head to the ground where the correctly inflated tyre is centred. The difference between the steering head centre line and the vertical line through the front axle is the amount of trail. If you have no previous reference, then ensure the trail measurement is close to a similar machine.

Mark the projected steering head centreline onto the floor, as accurately as possible. Drop a line vertically down from the front axle to the floor. If the bar can be laid along the side of the steering head, then the accuracy can be done more easily. The difference between the centreline of the steering head where it intersects the floor and the centre point of contact below the front axle, is the trail. Mark the final amount of trail on the drawing for future reference.

To accurately align a floor mounted machine when seen from the front, check with a spirit level noting the bubble position. Mount the spirit level vertically on the rear rim and compare the bubble position, then fit to the front rim and adjust to give the identical bubble position. Check on both the right and left sides.
Fit the spirit level on a set square and lie flush with the rear rim, rear sprocket, also the steering head itself and the front rim. Measure many times, then tack weld the steering head in at least three places on each frame tube.

On some customs, the front end is usually the steering head, although hub centre steering and other options are also available. The distance to the nearest upper and lower engine or suspension mounting points will usually decide the general shape of the front of the hub centred frame and often easier to align on a jig.

For many customs in side view, the front part of the frame may not look quite right with straight tubes, so tubing may need to be bent for giving a better shape to the tubing. Custom bikes often look good with a gently reducing frame taper or swan neck, but this must be strong. If the steering head support tubing makes a triangle when seen from the side and from above, then this is unlikely to flex, with only a few fillets or gussets needed to keep the head stock from distorting under load.

Extreme swan necks in the Swedish style may need extra support near the headstock to prevent distortion. For those who want to keep the clean lines on their front tubing, the usual side fillet plates can be replaced with a much stronger central fillet plate between the frame tubes. This must be fully welded to the steering head before fitting to the tubing, so that it is welded securely in an area otherwise impossible to reach. Such bikes will often naturally have a well supported head stock as they often employ tubes over and under the engine, which naturally curve up to form a sculpted head stock area.

Where it is necessary to measure lengths, use a metal measure, as cloth ones stretch. Always use a metal tape measure which uncoils straight, ensuring greater accuracy. One millimetre accuracy across the length of the whole machine is good, five millimetres overall is a little too sloppy, although acceptable on some commercial machines.

Fully weld up the steering head, but do not add fillets yet.
It is better to weld the steering head with bearings in place and damage them with the welding heat, rather than to hammer them out and possibly damage the headstock alignment. At least place lots of tack welds enough to allow the bearings to be gently removed without upsetting the alignment. Heat damaged bearings will do for initial road testing, but must be replaced for road use. Cover them with a smear of high temperature grease while welding. New bearings can be fitted after initial testing, a distinct advantage of using commonly available parts at sensible prices.
If the steering head bearings are expensive, then fit the steering head to the tubes and rotate it so it highlights by rubbing the areas to be dressed to make an absolutely perfect fit in the tubes. This will allow disassembly of the bearings and welding the bare steering head into the frame tubes without bearings. If the fit is perfect, then the alignment should also be perfect. Alternatively, if special pullers are available which will not upset the steering head alignment after some tack welding, then this is acceptable to remove the races. Do not hammer the bearings out, as a misaligned steering head is infinitely more expensive in the long run than a set of head races. If the races are to be replaced, then leave them in place during welding, to help reduce distortion of the important cylindrical accuracy.
Always ensure perfect alignment with many tack welds, so the final, full weld does not misalign.

When satisfied, fully weld the steering head.
Then reassemble the rolling chassis and test under maximum load to check for distortion.
Allow bearings and other components to settle, then adjust and then make a further alignment checks.
Slacken all engine mounts and swing arm bolts, then retighten to allow the frame to settle. If the accuracy is still acceptable, add the steering head fillets or side plates.
It is far easier to tweak the steering head to perfection before the various side plates and fillets are fitted.

Checking the front end accuracy from two independent methods will allow an accurate frame.
If anything seems wrong, take time to find out why.
You can now load the rear of the frame to finalise the optimum positions of the rear suspension unit(s) to find out where the shocks will give just a little static movement with one rider. Then weld the shock into position and test further until satisfied.

Take your time at this point and give yourself a good long breather.
Once again, weigh on bathroom scales and check front and rear axle loadings with normal rider(s).

Do not paint the frame.

Where a big engine is fitted, then you may need to remove the engine by having one or more of the lower frame rails removable.
If particularly heavy, possibly in the Munch Mammoth tradition, both bottom frame rails could be removed as part of the engine and supported on a rolling dolly. This will require a much stronger design of upper frame which can be lifted off the engine. This is a system used on a favourite recent V12 trike project where the engine was extremely large, allowing it to be removed whole, ensuring easier, safer removal.
When building a removable tube, first get the main frame strongly tack welded in position to keep it all together. Do not use full welds at this stage, as distortion may be incurred, causing springing when the tubes are cut, thus helping to misalign the frame.

Support the engine just enough to take the load off the frame, but still keeping it in place on the machine. Then cut the tubes where needed to remove the engine. A hacksaw blade is ideal as it removes the minimum amount of frame tube. An angle grinder with cutting disc will remove at least twice the width of a hacksaw during cutting. Do not use undue force when nearing the end of the cut, or distortion of engine alignment may occur.
Slash cutting the tube will allow the removable tube to rest on the rest of the frame. When done properly, can be self aligning with easy removal, by ensuring a little fail-safety as the engine will need to be lifted slightly for removal.
With the engine remaining supported, undo any engine mounts and remove the tube. Such tubes can be secured in place in many ways. The simplest is employing a slightly larger diameter tube which is split lengthwise, to become a pair of semi circular shells. The inner part of the split tube is welded to the bottom of the fixed frame rail, and the other half welded to the removable tube. This allows the bolts to fail but the engine to remain in a fail safe position under gravity.
Only tack weld these half tubes in position, so the tube can be checked for alignment and removal.
Where through bolts are used, the inside of the frame tubes will need spacers to prevent the frame tubes from distorting when the bolts are tightened. Solid versions of split bars are also possible, but only needed for heavy machines and will require an engineering firm to make matched pairs. Also study commercial motorcycle split frame tubes for alternative mountings which can be recycled.
When satisfied, then the split tubing joins can be fully welded. Then fit bolts and release the engine weight and check for frame distortion and adjust as needed. The rest of the frame may then continue as mentioned above. (This is an advantage of building rear first, as all distortion is sorted before the steering head is fitted.)

Reassemble the parts including the engine, suspension, forks and wheels. Temporary fitting of the suspension should now be done to assess the frame strength.

Testing of just the basic frame can be done prior to other attachments. This will also help to decide it the main part of the design can get away with lesser components or not, or if you need to do a major frame rebuild.

Remove any blocks and with two people on it, jump up and down, give it a really hard time.
Simulate hard front braking by rolling it gently into a wall, just enough so that any front fork suspension will just bottom out, many times.
When static test loading, do not block the wheels, as they must be able to roll freely to allow any deformations in frame shape.
Jump up and down on the rear suspension mounts (and also hub centre steering front ends) to get the suspension to move fully. It is important to get the suspension working fully as it is close to the maximum loading the chassis should take.
As a group, kick the wheels really hard from the front, back and sides to simulate rocks and kerbs. Where possible, try to twist the frame and suspension, while observing from the front, by blocking the rear wheel in a door way and twisting the front wheel or forks.

After this disgusting act of gross abuse, inspect everything carefully, especially where the wire model broke.
If it fractures or breaks, you have everything on hand to modify and repair it.

Load to max, see how it flexes, then think, tweak, add cross braces, fillets or extra tubing as needed. It is better to do this now, rather than after the paint and expensive work has been added.
This is initial structural testing. - DO NOT OMIT THIS. You know why, so don't delude yourself. See also testing later.

The main part is now completed, give yourself a pat on the back, you deserve it.

Take a long look and try to see the underlying form and function of the whole machine, the support engineering and the overall form and style. Even an excellent rolling chassis and engine can be turned into a pile of poo it not finished decently.
Poor integration of the rider and styling can spoil all this good work, so do not let standards slip.

Now is a good time to scrap the frame if you are not fully happy with it. Start again or modify as needed. It is better to do this now, then after all the other the bits and pieces are fitted.

Now that the main frame is in place, the next stage is to fit the parts which take priority over all minor items.

A major part of the build sequence involves the axle loadings.

Start with the solo and dual rider ergonomics as first priority, by checking the axle loadings by placing on bathroom scales, then positioning the riders appropriately.
The reason why clip-ons are in front of the fork legs, but touring bars are often far behind, is because it's all to do with ergonomics and axle loadings.

Once the overall weight balance is correct, the steering controls and linkages, foot rests and gearchange may then be considered.

Rider positioning has a natural hierarchy, where the rider is best positioned for axle loadings, then the footrests and handlebars positioned for comfort and control.

Once the basic frame and rider position with suitable axle loadings is defined, then minor and detail work can begin.

Minor components can find their best positions later. You may have to juggle these with the airflow for the radiator mountings and to a lesser extent the fuel tank position.
On conventional motorcycles, rider optimisation is often done with blocks of wood and cushions until the rider(s) is perfect. Then followed up with trimming cardboard around any radiators for basic styling or aerodynamic clearances.
On heavier machines, bathroom scales may not suffice, especially with two riders and simulated luggage. In such cases, it may be necessary to use four cheap bathroom scales linked as pairs by short planks.
See also balance later.

An example sequence of building a wrap around frame.

The rear wheel is built first to take the best possible tyre, then the rear sprocket and it's carrier or cush drive positioned and mounted for the chain to clear the tyre. Similar sort of arrangement for shaft drives, although the shaft may be allowed to deviate slightly in plan view if bearings and drive joints permit.
The swing arm is built and positioned to clear the tyre and chain and the swing arm pivots will be decided by the main drawing and any engine requirements.
If the rear swing arm is a straight forward design, then it can be assembled and welded on a flat surface on four Vee blocks to support the rear axle and a spindle running through the swing arm pivots or bearings to ensure prefect horizontal alignment. Before welding fully, ensure both the swing arm and the rear axle shafts are parallel, from side view and rear view by eye, and from above using a stud bar with nuts as a comparator. Return to the jig after fully welding, to check it is still accurate. Tweak as needed, then add any fillets or strengthening gussets.

With both wheels clamped between planks, use blocks and wedges to place the engine in position. Place the swing arm in the rear wheel and rotate it to a position relative to the engine sprocket to minimise rise or squat when under power as mentioned earlier.
If there are chain adjusters, then these must be checked so the swing arm is parallel as seen from the top. Use stud bars and nuts to compare with bar through rear engine mount.
Align the engine to the rear wheel or axle unit using the chain or shaft. Do not use the chain to align, but use a straight edge on the rear sprocket to position the engine sprocket. Double check by rotating the rear sprocket if possible and always ensure the rear axle is tightened. Check the chain run is parallel to the rear wheel rim. Then lay the straight edge on the front sprocket to check the engine is aligned. Block the engine in position and mark it so that any unwanted disturbance will be noticed.
Gently fit mounting bolts in the engine. Use old engine brackets if available or build strong mounting plates or tubes onto these bolts and lightly tighten the bolts carefully. Build tubing or sheet to create the rear engine mounts and swing arm mounting area.
Build up tubing towards the rear upper shock absorber mounting area, but do not add the upper shock mounting plates at this stage.
Position the steering head on the forks and move it slightly forward to allow a little extra metal for alignment and building around the steering head later on in the process.

Bend one main (often bottom) frame tube from the engine mounts, to curve up towards the steering head. When the bend is correct, make a symmetrical tube. Match, cut, shape and then carefully trim as a pair to fit to the rear engine mounting assembly if required. Gently grind the engine mounting tubes to fit, never compromise the main tubes or nudge the engine.

When the main tubes are accurately shaped and trimmed to fit, then tack weld just enough to hold the assembly in position onto the rear engine mounting assembly. Then accurately position the rake of the headstock tube to rest on the on the frame, allowing some spare metal which can be trimmed later.
When satisfied, apply a minimum of three tack welds per joint. In some cases, some tubes may prevent full welding of deep components, so these must be fully welded as possible before fitting other frame components onto or near them.

Build up the rest of the frame, checking for adequate clearance to remove the engine and also clearance for carburettors, exhausts and such like.
Remove and fully weld up the rear of the frame assembly and main frame tubes evenly from both sides to minimise distortion. Then refit to engine and swingarm and wheels in the jig. There may be some distortion, requiring the mounting holes and brackets to be dressed to fit cleanly and / or some tweaking of the frame. Check alignment and tweak or modify as needed.

The front forks and head stock can now be positioned onto the frame tubes. The headstock will need to fit without gaps and requires careful fitting. There is no substitute for careful work. Gradually grind the main frame tubes until perfectly aligned, then tack weld in position and double check. Remove bearings with pullers or leave them in place. Fully weld front end.

Reassemble the rolling chassis with engine. The tyres can now be pumped up fully if they were clamped between two planks.
The shock mounts can now be positioned temporarily and the bike loaded to see how the shocks react. Check the shock spring adjusters are set in the standard or light load position. Carefully sit on the machine and expect the shock to compress just slightly. Adjust the position of the shock mounts on the chassis until correct, usually compressed slightly with one rider for optimum suspension with adjustable shocks set at soft.
If the frame is tested with the shocks in the tack welded state, it will show up any flexing in the rear of the chassis and any weak areas, possibly from structural points of high load or poor design. Fully weld the shock mountings when confident.
The areas around major mountings may now need to be improved by the support of fillets or gusset sheets between the frame components. To even the stresses, make smooth curves where they fit the frame to help the loads to dissipate evenly through all three dimensions. See also Phil Irvings excellent book, details at end of monograph.

The engine may be difficult to refit in the frame if distortion is high, so take time to check why any engine bolts do not fit easily.

When static test loading, do not block the wheels, as they must be able to roll freely to allow any deformations in frame shape.
The average frame is supported at each end and loaded by the rider and engine somewhere between the middle and the rear. This will cause the top of the frame to be compressed and the bottom of the frame to be in tension. The engine mounts can enable the engine to act as a lower beam to prevent such bending.
When loading to ascertain flexing, view from the side, top, front and rear. Look out for wheel misalignment and general weak areas which may improve with a few cross braces or gussets. On asymmetric frames, make particularly careful checks from both the front and rear views while under maximum load.

Tension may be a problem. This may try to pull tubes out of the end welds and fillet plates or gussets often help.
Compression may be a problem. This may cause tubes to bend or buckle, so secondary support along the tube to prevent this is useful, otherwise, extra, or heavier tubing on the compression side should be contemplated.
Torsion may a problem. This will need careful use of cross bracing and fillets if needed.

Consider all possible ways the design will fail and redesign to eliminate possible problem areas at this stage. A rough guide is to try to build with imperceptible or acceptable flex at twice the full rider load plus luggage. If the early tests flex more than required, then judicially apply more material until flexing is reduced to acceptable levels. Many proddy racers add a few extra tubes to make a commercial frame handle better.
Any acceptable flexing at twice load should be appropriate for that needed to keep on a straight line when landing off a hump back bridge. For trials and motocross, then the safety margin must be adapted, especially if the suspension is to be set with stiffer springs and hard damping.

Finally add any tubes, screw mountings, and other design considerations that need to be fitted for the main components such as removable rear frame, or upper removable engine mounting plates.
Do not paint the frame.

Adaptability is often a wonderful attribute, as a lug, bracket or shock mount can be welded to a basic frame component, then simply ground off and replaced if later deemed unsuitable. This need not damage the main components and can often be done without having to dissemble the machine, which can greatly help to reduce development time.

Refining the basic rolling chassis.

For those who build custom machines regularly, it may be preferable to mount two scales in the workshop. By choosing scales with electronic displays, these can be wall mounted for much easier assessment of the axle loadings and to adjust rider position. Most displays can be modified with simple extensions for the LED displays. This allows the rider to move to the optimum position and allow the passenger load to be assessed to best effect during the building process and before finally fitting the seats, footrests and handlebars.

If making your own wind tunnel, these can be integrated to assess the axle loadings as the wind speed changes, highlighting any dangerous changes in overall loading and balance at higher speeds under the influence of a poor fairing or other factors. See aerodynamics also on this website.

For posing custom chops, the best riding position can be created, possibly with a full length mirror for the ultimate mean, or cool, or Hollywood image.

When seen from the front, always try to get the bike to balance vertically before adding the rider. This can be helped by battery placement and other components, but is not always possible to get perfect. Some bikes now position the battery low and beside the engine, opposite the single sided swing arm for obvious reasons.

Sit on the machine and check the alignment as seen from the front. Adjust the seat and rider position so the machine will lie perfectly vertical, and with the intended wheel loading front and rear.
There is nothing wrong with setting the seat just a few millimetres offset if the bike and rider end up sitting upright. The main considerations for fitting a seat are to keep the wheels upright when properly balanced, aerodynamics and for the riders best posture and safety.

A slight offset may make upright riding more comfortable, especially on a machine where the weight is offset. If the seat is positioned for best balance when the wheels are perfectly upright, this reduces the poorer ergonomics of a rider sitting slightly off the seat to balance the machine, or a poor spine to pelvis angle. Riders are part of the machine, so always integrate to best effect. The seat can now be added as the last major chance to balance the machine vertically as seen from the front, and also the optimal loading between the axles.

Now check the cornering clearances and adjust the foot rests or running boards and the side stand lug as needed.

The passenger, luggage and fuel are the main masses which will upset the best overall fore-aft weight balance. Ideally the passenger is close to the rider, but most unlikely to be ideally positioned, often requiring the rear suspension to be adjustable for two riders. Likewise luggage can be problematic, although good design should be capable of offering forward luggage for some heavier items for better balance. See also luggage and fuel system later.

For dual riders, the seats can now be fitted. It may be favourable to make the basic seat profile and the handlebars without their mountings at first, to help reposition components from any conflicting requirements. See also handlebars later.

Imbalances do not only occur only when the machine is static.
Speed sensitive imbalances caused by aerodynamic drag of asymmetrical positioning of radiators and other items or design profiles should also be avoided. A non-symmetrical aerodynamic shape may not be noticeable at low speeds, but will upset the balance increasingly with speed, with most effect at top speed. If fitting certain items, such as two radiators, they should be mounted symmetrically about the centreline for high speed machines.

Encouragement.
The above offers much towards spending a lot of time and effort for a decent frame. Unfortunately It can also cause readers to decide against bothering with the effort entailed. It is better to make an adequate frame than to be frightened off by too many expectations of having to make a perfect frame or the costs of time and effort.
If deciding to try a rough frame rather than take the effort of professional levels of design and manufacture and testing, possibly on a tight budget and using the remaining off-cuts used for gussets, then do so. It is preferable to make a second rate machine than to make none at all.

It is not uncommon for a roughly built machine to offer superb handling and be lighter than expected.

Seats.
Most motorcycle seats leave a lot to be desired. Touring machines fare a little better. Only recently was full comfort possible on motorcycles, commensurate with most quality cars. (The JP7 used car seats and squabs.)

Seats support and contain the rider and passenger, who are the most important load for a machine.
For conventional motorcycles, seats are basic. For other seat structures, see the companion monograph: 'Builders guide to composite HPV design', which has a large section devoted to recumbent seat design.
If intending to use a full seat similar to cars, or the base of a car seat, perhaps for the passenger of a touring machine, or inner city taxi bike, then begin with re-engineering car seats, These will allow adjustable squab (backrest) angles.

Standard car seat foam is an excellent starting point for ergonomics on ordinary bikes and touring machines.
Most other motorcycle seats can be recreated from salvaged seats, which have ideal foam densities and often have adaptable steel bases.
If a plastic seat base needs to be replaced by a steel or composite unit, then it is often best to use the frame itself as a former for light panel beating duties, then lifting the base off the frame by employing rubber blocks from an old seat. Simply cover the frame with a spacer for moulding plastic seats, or a sheet of old inner tube or blanket, if panel beating a metal seat in situ. The sheet of alloy or steel is then gently hammered into shape over the frame. Fibreglass or composites can be draped over cling film over the frame with rubber blocks temporarily tacked in place on the frame. The layers of fibreglass can be laid up on an old sheet of glass, excess resin rolled out, then the fibreglass draped over the prepared frame areas before it sets.

There are many ways to secure seats and the design of the machine will define the best method. There are many hinges, lugs and catches available in the motorcycle and general automotive industry and in hardware shops too. Garden gate hinges seem good for simplicity and sturdiness.

Covering seats is often available locally, simply by asking at a local bike repair shop.
Vinyl and other materials are commonly available. Many will stretch to fit within reasonable limits. For those who cannot sew, thicker vinyl sections can be turned inside out, then welded by using a soldering iron pressed gently across the inside of two vinyl sheets, preferably with a steel rule to guide the line and reduce heating of the rest of the material. After practice, such welding should give a strong, wide seam, which is also waterproof. Do not overheat the material. Use a stipple action with a warm soldering iron to ensure full penetration of the heat.

For racing machines and trails bikes which need minimal padding, thick camping foam can be firmly bonded to the seat base and trimmed with a sander, without the need for any covering. Always use the better quality closed cell camping mat foam, which does not crush with extended use and does not absorb rain. There many foams available which can be applied with glue.
When dry, a polythene sheet rubbed with a removable marker such as lipstick is then laid over the seat, and the rider sat in position then encouraged to wriggle about. When the polythene sheet is removed, the riders support areas are graphically marked. The supporting areas profiled to match the rider and the non supporting areas can be trimmed and shaped to remove unnecessary areas. This will improve both ventilation and reduce weight. A powered sanding disc is ideal.

For steel seat bases, allow drainage, lightening holes and use a narrow tapered spike to make securing tags around the edges if securing vinyl to a steel base. Reprofile the solid end of an old, large drill to make the spikes, and strike through the steel base when supported on a wooden block. Glue split piping around the edges of a seat pan to reduce the vinyl covering from being torn, or for greater strength, create curved flanges around any sharp edges. Extra rear structural support can be built up in light of rider contact areas. This is especially important for passengers on powerful machines, where a rear seat hump prevents them being left sitting on the road after a sharp start. Do not permit any sharp edges or anything that may cause harm.

In all seat mountings, the weight of the rider and pressures created when accelerating and while riding for many hours must be considered. This is particularly important in removable or pivoted and full length seats.
All grab handles must be frame mounted.

As both rigid and soft seats with squabs (back rests) are often built from dual rails, there are a number of natural, organic and / or stylish ways to mount the seats in an interface with the frame. When seen from the front view, the seats must spread the load evenly into the frame. From side view, they must also resolve the rearward pressure from acceleration.

When mounting a full length seat with squab, sit in the machine, relax and balance. The machines wheels must be perfectly vertical. Unlike a conventional machine, a recumbent rider cannot lean left or right to compensate for an imperfect design or manufacture. This must be solved while static at an early stage before permanently fitting the seat. Final adjustments may be accomplished with battery placement etc. Various forms of adaptive, interactive seating are under study as part of the JP8/9 series and may be described as development progresses.

If building a comfortable machine and intending to tour, then use design to maximise enjoyment. For many touring machines, the art of combining efficiency with comfort is very important indeed. Building a machine from scratch wildly liberates the riders capacity to tailor the ergonomics and load systems to total personal preference.
All bikes should be comfortable for MANY hours of constant riding in most conditions. Bikes soon loose their advantage over cars if the riders have to stop every hour or so to stretch and exercise, or warm up or to dry out.

Centre lines are important, the wheels and centre of mass of the combined rider and machine should be on the same vertical plane when ridden. Use a plumbline or piece of weighted string and a large mirror to ensure the rider/machine is set up so the tyres are perfectly vertical when rider is sitting comfortably in the riding position.

Handlebars.
The conventional handlebar tube is the most sublime form of effective simplicity.
Many people have tried to re-invent the standard handlebars, but even the best designs cannot improve on simplicity. The only advances are in materials, their dynamics and ergonomics. It is this simple approach that should be applied to all designs.

The luxury of simplicity is unfortunately not available to some machines, such as those with hub centre steering. For many, the handlebar is a tube bolted to the top of the forks.
For others, the rider is seen as the primary, ergonomically ideal form, with the handlebar position dependant upon the rider.
As a young biker, I once sat on an MV, closed my eyes and put my hands where they should be, the handlebars were less than 2mm out of my ideal vertical, horizontal and width positions. All my bikes have had to pass this test.

Although common on HPV's, underseat handlebars are rare on motorcycles. The author uses them on many motorcycles and recommends that they should not be underrated. There are also many other alternatives to handlebars, with some Japanese concept machines using dual levers and other routes also available, so the builder may consider if anything is preferable.
Always be very careful when testing and developing new control systems.

For long distance relaxing touring, the rider may wish to have secondary hand and foot positions to reduce strain or similar problems. Alternative foot rests are common practice on chops and touring bikes.
A second, alternative palm rest or similar can be made available for the longer, easier sections of road. This could include hi-fi controls, although advances in voice control may now be preferable for enclosed machines or within full-face helmets.

Where simple brake levers are used, their mounts can be built into the handlebars to reduce weight. But integrating master cylinders may cause problems. Be warned that a simple crash may damage a highly integrated handlebar system. Using standard fitment levers, switches etc, will allow much easier damage repair and replacement.

Steering.
Rake and trail should be copied to some extent from standard machines, especially where forks are used. Hubcentre designs can have the luxury of adjustable rake and trail, as enjoyed by ELF and many others. Rake can be adjusted while riding, as enjoyed on some of my JP series machines.
Remote steering is an opportunity to revel in the various layouts and optimisations available, which happily involve superior ergonomics and adaptable ratios. Remote linkages are usually for hubcentre designs, although forks can be controlled remotely too, such as across a V12 trike engine. Setting up the steering for optimal handling is done during the testing sessions.

Steering linkage.
For some machines such as hub centre steering, once the handlebars are ideally positioned, the steering linkage can be built for best possible routing and to ensure clearance from other components. Whether low or high handlebars or levers are fitted, the clearances should be fully understood then reassessed and finally the design adapted to fit the actual machine.
There are many convoluted routes for remote steering and all have advantages and disadvantages. For best results, direct linkage offers fewer components to fail and maximises feedback. The conventional handlebar remains the definitive form of simplicity with effectiveness.

The geometry of the linkage can be very important, especially on multiple linkages. Design in full size on paper just what is needed and build in possibilities for variations during testing. If temporary handlebars with many mounting holes are needed for testing, then so be it, as this is always worth the effort to get close to perfect during initial testing. Pun intended.
Always try to position a linkage arm to be ninety degrees to the pivot. This gives maximum leverage and minimum geometrical distortion across the movement. In plan view, any angular displacement of the link arm pivot should be mimicked at both the handlebars and the forks and vice versa. They should ideally be 'geometrically similar'.
Where simple runs are not possible, such as hub centre steering, refine the angles with the steering arm path to the front wheel, so all angles are evened out though the path of the steering linkage.
The integration of the steering can be an opportunity, as some vehicles integrate ideas such as connecting headlight alignment to the steering. An enclosed machine can integrate low speed stabiliser leaning with the steering linkage for better low speed manoeuvring and while parking and reversing. See JP7.
Testing may need to modify the design the linkage and possibly need to be adjustable for length. This is often applicable for changes in rake angle which can change the linkage position. Wherever possible, always position the linkage pivots in neutral areas, where such changes will not upset the linkage or alignment. Adjustment in linkages is worthwhile during testing. Where intermediate arms are used to test ratios, they can be made in adaptable materials until a final design is achieved.

Steering ratios can be adjusted on hub centre or remote steering designs. Biking should be fun, or at least convenient and comfortable. The forces needed to turn a front wheel are not high, especially when rolling. Even when encountering pot holes and excessive cambers, a well designed machine should easily maintain its own stability. Therefore only light pressure on the bars should be needed to maintain control in most conditions.
As well behaved motorcycles employ steering based on gentle pressure, rather than angular movement, the handlebars can be 'geared' for a reduced handlebar movement.

The longer the wheelbase a machine has, the greater the steering lock needed at the front wheel. This is required to turn the same sharp corners that other conventional bikers can more easily accommodate. Building and refining such levels of steering lock into the design is often easier with adjustable steering ratios.
Initial design using 1:1 steering ratio will mean the handlebars must have full lock and this can make them wider than is preferred to clear the rider. Large handlebar movement may also cause awkward wrist positions and possibly reduce the riders gearchange or brake control.
On steering linkages, there may be a trade off with heavier steering during pulling away from a standstill, but this is usually more than offset during the riding. Larger front wheel to handlebar ratios will reduce wrist angle problems. At mild ratios, any lack of control is not noticeable while riding. Where possible, be prepared to experiment with adjustable ratios until an ideal personal preference is achieved. Final choice will depend upon the riders requirements and the controllability transfer during the phase from stationary to self stable riding. Slight variations from 1:1 are very difficult to recognise. Only when ratios around 1:2 are reached may problems begin for some machines.

Much road testing on hub centre steering JP series machines has been done quite happily at 1:3, handlebars : front wheel, with handlebars positioned conventionally, above the legs on recumbent machines, and also below the seat in the low recumbent style. Although the author prefers the latter on road machines, it is very unusual for most motorcycles, even if extremely comfortable, see right. (Riding in such a relaxed position at 70 mph for hours across Bordeaux and thrashing Llanberis Pass is sheer delight.)

Always ensure the linkages are smooth and 'tight', to ensure maximum feedback to the hands.
Unless absolutely necessary, always keep the paths of linkage pivots reasonably parallel to each other. This ensures all linkage arms can use simple connectors. This of course, is not always possible, but the path between the steering head angle and the handlebars pivot should ideally be a straight line, or in real life, a series of gradual angle changes across any linkages. Steering connections should use spherical connectors unless the linkage is properly aligned.
There are many ways to make the linkages. All must be free of play, yet friction free. Small spherical ball joints are the common method of mounting. The industry standard spherical links are often known as Rose joints and can be seen on the suspension links of Formula One cars and many custom bikes. (Do not use the cheap type used o many production bike gearchanges.)
Where compound links are close together, then two arms can be simply linked with a spring which eliminates any play under all conditions permitting primitive, friction-free links. This set-up maintains excellent control, even with badly worn pivots.
The above also applies to gearchange and brake linkages etc.

The riders wrists, elbows and shoulders are also part of the steering control linkages. Treat all steering linkages with equal care.

Chain run.
The rear wheel will control the centreline, so the rear sprocket is next in the line of the alignment hierarchy. A straight edge along an accurately aligned rear sprocket will define the engine sprocket position. Test the alignment four times with the rear sprocket and wheel rotated through steps of ninety degrees, as this will help to eliminate compound inaccuracies, especially if on a rubber mounted cush drive, or if the chain has tight spots. Likewise for the front sprocket. Use a new sprocket and fit to a clean engine. Check it runs true, then use a straight edge so the engine lines up to the rear sprocket. Chain tension and its requirements when mounting an engine is as mentioned earlier.

The chain must run clear of the frame and swing arm at all times. If regular chain breakage's are expected, such as enduros in deserts, trials or motocross, then ensure there are chain guides which will always deflect a broken chain through the front sprocket and dump it safely on the deck.
Good design should prevent rubbing on the swing arm, but replaceable nylon rubbing plates should be used where chain rubbing problems occur. Most motocross components can be adapted. Metal rubbing plates cause unwanted noise, but can be most applicable during testing, to warn of impending problems.

The use of aftermarket chain enclosures is possible in place of chain guards, as these often have central ribs to reduce wear while guiding the chain. Often found on touring bikes with chain drives and on 80's Montessa trials machines in place of chain guards.

On machines which do not have concentric engine sprockets and swing arms, then some chain flexing is unavoidable. Always run the machine when assembled on it's centre stand or test rig to note possible fouling points. Use the rear brake to simulate load. Always test in the worst case scenario, with the chain at maximum slack, so wear and any nasty vibrations can be assessed at an early stage. Always remember that the top run is tight most of the time, with the lower rattling around as the main offender, but during engine braking the top run becomes the main offender. If excessive vibrations occur, check wheel bearings, cush drive and sprocket alignment. Preferably test with badly worn components.

A good design should be able to cope with a bad chain. Testing with new components ensures good alignment and makes for an easy life. Real testing with both good and also badly worn components makes for better machines.

Blocking off the ground safely, then running prior to road use is paramount, as it beds in bearings, partially worn or suspect chains and brakes, shows up vibrations, while initially testing brake torque arms etc. Revving up and slamming on the brakes many times helps to try to rip them out of their mountings, as they would be on the road makes for a more reliable build. If the mountings fail at this stage, then the rider will have no broken limbs and helps to prevent hospital trips later.
Static running with the rear brake on until it smokes or glows will help to decide if a race set-up is adequate, and also checks that the brakes are properly serviced. Then consider deglazing or replacing the rotor and dressing or replacing the pads. Then use the opportunity to gently bed in new components. There is no excuse for poor brakes.

Never send an incompetent machine out for road testing.

General airflow.
Once the main components are in position, rider, engine suspension and wheels, then all else is variable.

The ability to vary the tertiary components will allow optimising of the design, especially the weight distribution and airflow.
If road racing, then seating so the rider is compactly but safely in control can now be refined. If touring, then the most comfortable seating is also refined at this stage, before the final decision for the rear frame and seat rails. this will ensure the rider gets minimal buffeting at speed, for aerodynamic racing efficiency or for touring comfort, or preferably both on a road bike.

Air cooling airflow for air cooled engines, or radiator position is of paramount importance as is bike stabilty at high speeds, where buffeting can get dangerous.
Asymmetric positioning of radiators and other components which affect the airflow and subsequent offset pressures at high speeds may need to be avoided. Always position radiators centrally or with dual radiators either side of a very high speed machine. This applies to all major aerodynamic design aspects and components. Asymmetric imbalances on high speed machines is often easily controlled, and all possible problems should be eliminated early in the design process. Asymmetric design is acceptable on low to medium speed machines.

Always consider aerodynamics as part of the design, not only for better top speed, but better handling, fuel economy, reliability and most important of all, for comfort. The prime design component of a touring machine is the rider, without which the machine is merely an academic exercise.

Never sculpt the aerodynamic design of a machine as a styling exercise unless touting for work in a posing firm, where money and status usually come before true effectiveness. (Surprisingly common in far too many design studios who rarely make a truly road legal machine.)

Form should follow function. Perfect form follows perfect function. From the dolphin to the eagle, from the Spitfire, to F1, true and honest quality of design can only come from a pure direction with a careful approach to design.
Designing for commercial or corporate image can often compromise design from the outset. (Even Lotus can recognise a Lotus ethos design, even though it may not be designed by them and has only two wheels and powered by pedals.) Aerodynamics can be used to influence both potential buyer as well as the airflow. Use to best effect.

The basic components can offer a starting point for the air flow use, with aerodynamic dead spots used for passive components such as battery, which can even be positioned to help smooth airflow for efficiency. The stable, active 'clean' airflow areas can then be put to use, mainly to transfer heat from radiators and to cool the exhaust or wherever the need is most effective. Aerodynamics is also discussed later.

Gearchange.
Standard gearchanges are simple. Remote changes may be problematic. Sophisticated pneumatic or electronic gearchange systems can take a long time to refine, unless the initial design of the control has many variables built into the design for genuine interactive variability while road testing.

The slickest gearchenge I have ever used is a hand gearchange on one of my ultra low recumbents, where the gear lever was just inches away from the handlebars and integrated with a slick clutch mechanism.

For foot gearchanges, wherever possible keep the sweep and angular displacement of a gearchange relative to the lower leg and foot angle, and the same sweep as standard machines.
Cables tend to give sloppy changes, so tie-rods are always preferred. Where cables are required due to their ability to follow curves, then consider some car clutch cables, or even aircraft cables, some of which have excellent push-pull properties. Cessna throttle cables have been successfully employed as gearchange linkages in Messerschmitt micro car gear linkages. Some heavy car clutch cables make excellent remote gear linkages when used on lighter linkages.

Long single rods are better as they eliminate excessive pivots and subsequent wear and sloppiness. Where long rods are employed, flexing can be controlled by many methods. The simplest is replacement with a tube, possibly including a gradual increase in the middle tube diameter, such as using old golf club shafts, tapering puch bike frame tubes or by using intermediate guides. Guides can cause friction if not aligned well.
Always fit to personal preference and allow some adjustment, especially on test machines. Intermediate linkages can be made as per steering linkages as mentioned earlier.

Adaptation of quick shifters to electronics are comparatively easy, but fail safe measures MUST be employed. When employed for road use, these can be integrated to read the tachometer and throttle sensors and possibly adjustable for economy, sport settings or to be speed sensitive. They may be set up to shift only at red line if needed when at full throttle, with more sensible variations also available according to personal taste. Changing down can also be adjusted so that twisty roads can keep revs higher for better engine braking with fourstrokes in race mode. On steady straight roads the gears can be changed to keep revs lower for economy. Variations will require direct control by the rider, or set-up for automatic use according to the road, hence the usual options of race, road and economy settings and this will require inputs from the engine, throttle and many other sources.
The control system can be electro mechanical for simplicity, where simple sensors are adjustable for switching the consul servos and suchlike. If totally digital, then unless you write your own control code and debug it completely, it is often better to use after market systems.
The choices of control systems are infinite and not all are rider dependant. Such enhancements are close to being available for many machines, so should be considered if a design needs to be advanced in this direction at a later date.
Where appropriate, integrate as many variables as possible with easily adjustable rotary potentiometers for all adjustments for test rigs, preferably in real time while riding. Digital systems are not always better for development, as writing in machine code may occasionally cause unexpected problems. Once proven, analogue systems can then be modelled and shaken down in digital form once the concept works as needed.

Lean angles and safety.
When building the frame, look from the front to check the leaning angles and clearances needed. Assume a seventy percent sink in the suspension so that the machine does not scrape too easily on tight sweeping corners. If keeping to well made roads and speeds below 80 MPH, then you may be able to get away with less suspension compression, allowing a more luxurious, touring foot rest design.
Warning: Always make sure the first item to scrape is deflectable such as a fold back footrest, as this must ensure the wheels do not lift off the road, but that you merely get a warning noise and a lifted foot. If the first thing to scrape is solid, then you probably have lost the bike and expect to go straight to hospital.

Controls.
Always stick to standard international control layout conventions. This is mainly for emergency reactions built up over many years of riding for nearly all bikers.

If, like me, you build radical machines, then many people will want to test it. So always give new riders the best chance to be able control the machine in an emergency, by using normal reactions when things go wrong.
Sometimes complex handlebar designs may be needed, such as shown opposite for the JP2 series. In such cases, natural ergonomics and emergency reactions still remain the final arbiters of whether they are genuinely effective. Note all the parts carefully prepared for initial assembly and testing.

If changing controls, reconsider for an internationally accepted control system, where natural rider reactions are as expected, or consider a totally different arrangement which cannot be confused with natural reactions.

For all, including test machines, emergency braking should be possible with a single reaction, which reduces throttle and applies brakes naturally, yet maintain reasonably sensitive control and feedback.
On radical machines, always consult with many people to study natural human effects and reactions. Do not assume your own ideas are common to all. Never make a design which needs many hours to become accustomed to before riding. Do not allow a machine to be able to run out of control.
All my radical machines were easy to use and even complete novices took to them with delight.
Fail safe should be paramount, yet natural.
Where total lack of control occurs, the machine should instantly reduce throttle and the machine want to steer ahead or in a gentle curve as it decelerates.
After a long wheelie session, one of my machines ended up falling gently at my feet after managing an unmanned 30 foot diameter gentle curve, possibility the sign of a well behaved chassis.
During high speed testing where the rider may be thrown clear, an ignition cut-out should be connected to the riders wrist via a simple cord. During extreme speeds, such as record breaking in a caged chassis, consider an extra simple mouth operated kill switch which ensures the rider will maintain complete handlebar control with both hands.

Cables.
Routing of the many cables is often assumed to be simple and most times it is - if it is done well.
Cable routing can also be an art and when done properly, can enhance both the ride experience and the design. A stiff or awkward throttle or clutch cable can ruin a good machine. A well designed cable route can reduce weight, friction and wear, while refining steering sensitivity and improving feedback.
Smooth slick and with perfect feedback.
Cable and pipe runs should be safely routed to eliminate problems. Especially unsuitable bends, or allowing hydraulics to dangle by their pipes when a wheel is removed. This can happen with underslung rear calipers on minimalist tensile links for ultra light machines with lower centre of gravity. Also try to minimise flying stone damage on poor roads.
Where cable termination is difficult to position for a smooth curve, the Bowden cable end can often be pulled from either of the two directions of the connections. Choose the most appropriate and modify if needed. At each end, the outer can be 'fixed' and the centre cable pulled to apply tension, or the inner can be 'fixed', with the outer allowed to slide over the inner to apply pressure. Reversing the position of the cable on the mounting can also solve many cable routing problems with these four options.
Always allow a gentle transition curve from a straight pull open cable and back into a cable outer. The use of HPV mountain bike 'noodles' or gearchange rollers can greatly help refine the design of tight bends, such as awkward throttle linkages.
TIP: For clutch or front brake cable noodles, I use copper brake pipe slid into a steel car fuel pipe, then gently bend to shape while the inner cable is constantly pulled back and forth until supremely smooth. The steel gives the structural support, while the copper ensures a slick, friction free action. This can then be welded or clamped to my customs for absolutely superb smooth and neat cable runs, even in the most difficult places.

Simple cable guides can be easily made by simply winding wire around a round bar, slotting the resulting spring to give small circular lugs which can be welded or soldered to the frame. When set at thirty degrees to the cable run, these 'C's allow the cable to be easily slotted into the lugs and will remain in position. Bendable sheet tabs are also possible, but will fracture with excessive replacement and removal. Always position the cables to enhance the design or are out of sight.

The designer has total control over cable routes. If designing for lightness, then open cable runs are equally valid as for all machines such as push bikes and aircraft. Ensure there are a few rubbing blocks, as cables can vibrate against the frame, causing wear. Ski candles can protect the surface. There are many other possibilities including rubber bushes or small O rings on the inner cable, but even these will rub the surface. It is always best to put the sacrificial abrasion material on the surface to be protected such as the frame.
Ski candles are sticks of nylon-like material which when set alight, will drip the low friction plastic onto the required surface. It can then be shaped and smoothed. Old HDPE plastic containers also make excellent abrasion pads when melted into a suitable shape. (HDPE - High Density Polyethylene, as used for oil containers and also in hip joint replacements. )

All cable and pipe runs should be positioned to minimise stiffness at moving points.
On remote or handlebar linkages, such as hub centre designs, cable runs will flex much more. By positioning the front brake cable on the steering linkage between the handlebar and front wheel, rather than along the frame and swing arm, the amount of flexing is greatly reduced. This will lower friction, reduce wear and offer better, slicker control. Also applies to many similar linkages.
Where hydraulic piping is subject to damage, running the pipes through the frame or in a light surface tube may reduce problems. Properly designed, there should be no need for heavy steel braided hydraulic brake lines. The new aramid brake lines with alloy fittings look superb and are available in many colours. They can also be run though tubing for protection and for minimalist custom bikes. Where suitable then even the brake pipe can be eliminated, by running the hydraulic fluid through the frame - if the frame tubing does not flex.

Where colour co-ordination is required, always remember that nylon can be dyed. Any fabric shop can supply nylon dyes in a vast range of colours and these can often be mixed. This applies to bushings, brake outers and whatever else is needed, including tie rod bushings, clips and seat fabrics. Make all customs totally colour co-ordinated.

Brakes.

The advantage of the many standard brake components, is that they allow a variety of sizes and equipment to be used. Commercial items should always be a first choice, to ensure rigidity, lightness and many other aspects. Standard brakes can be modified with the many options of fixed and floating discs integrated into various designs.

The standard motorcycle disc brake is a natural choice for a high-tech machine. It is reliable, light, stylish and works very well, but has high spot loadings at its mountings which must be resolved properly.
The latest four, six and eight piston callipers are superb examples of art in aluminium.

Home made callipers are possible, often machined from billet using standard calliper components. Although beyond the scope of this monograph, they are not too difficult to make from billet, simply needing the bores to be drilled to match the standard pistons which are available off the shelf from most motorcycle manufacturers. Carving the outside can be done with any of many aluminium profiling tools. The only real difficulty is the recesses for the piston seals requiring a precision disc cutter or similar tool, and the drilling of the internal connecting lines with a long drill. )See also making your own bakes in the compisites monograph.)

Rim discs are effective but preferably purchased from specialist suppliers.

Be careful when using powerful disc brakes on smaller front wheels, as the rider may easily loose traction in wet weather.
One excellent study of mine used a multi piston calliper on a ventilated floating rim disc, while another design used more than one calliper on a single disc, both being part of the JP series programme. Always remember that too much braking power can be a problem too !

In cases where the braking is too efficient, the brake pads can be reduced by slotting, tapering, or stepping. Tapering allows a progressive learning curve up to the full power as the pads bed in fully.
Another trick in mechanical brakes is to fit a rubber section in the cable end to give a little cushion, or a small air bubble introduced in a hydraulic design. Bubble size can be carefully adjusted with experience. Neither method will damage the units and can be easily removed if unsatisfactory. Similar devices are commercially available.
All are old tricks from a time when steam engines ruled the earth.
One finger emergency stops are easily possible, but tend to be more dangerous than any properly set up and balanced braking system.

When mounting disc brakes onto modified or new hubs, ensure the mounting flange is oversize to allow it to be machined down to fit. Mount the hub on its axle in the machine and spin using the engine. Then use a temporary cutter on the swing arm to carefully remove excess material until the disc fits snugly. This ensures the disc will run perfectly true.
The retaining holes can then be drilled, by using the disc as it's own drilling jig. Drill a pair of opposite holes first. Alternatively mark one hole, then cut a concentric groove to align all the other holes around the flange on this pitch circle diameter. Use shouldered bolts or tap the holes and loctite studs into the hub. The bolts or studs need only supply a light positional fixing for the disc, their main task being to transfer the shear force safely across the disc to hub interface. It is the shouldering around the studs or bolts which is important. Secure firmly and always use a bolt locking device or liquid. IF no suitable shoulder, then a special metal carrier can be fabricated to mount to an existing hub.
Not all discs need be bolted to hubs or rims. Some phenomenal rim brakes have floated freely on just three slots as part of the JP5/6/7 programmes.

Where the frame and engine are complete, the axles and wheels can be built up using the bare axle as a dedicated lathe powered by the engine. See wheels later.

Whatever form of brake is used, it must be prevented from distorting when transferring the force from the wheel into the frame. Usual choices are to spread the load evenly into the nearer frame areas, or to pass it via an arm to a strong mounting point, often for anti dive purposes. Whatever type of calliper is used, the force against its mounting should be spread evenly across a wide part of the fork or frame to minimise distortion.
Stronger or deeper supports reduce chattering. Changing between compressive or tensile mountings can also help. The mounting must absorb the forces safely without distortion, or distort in such away as it is positive in effect, as misalignment during braking is not recommended. (Except in a few exceptional research cases where it is part of the intended design.) The calliper must always retain accurate position relative to the disc to prevent pad drag when released.

Rear axle, brake and other mountings can simply be built up from tubing, sheet or block to form a structural item which can then be sculpted to shape. Like good quality motorcycle axle dropouts, the use of careful design and sculpting will allow these to align and merge smoothly with shapes carved for smooth welding into the main components. Some commercial machines have sharp angled fillets where their brake mounts attach to the frame, do not follow suit. Always ensure smooth transition curves in all planes to reduce any natural fracture areas.
Brake mountings may be built into, or as part of the frame and can help maximise rear end support and braking force resolution.
If a floating brake calliper is chosen, (often as part of an anti dive or anti squat system,) the spacer on the axle should pivot smoothly in the mounting arm to reduce chattering. Needle roller is ideal, although a greased metal bush is common and may suffice in some cases.

Be careful when considering the torque path of brake mountings, as some lightweight tie-rod arrangements may collapse when holding the machine from rolling backwards when stationary on a steep uphill. Design such items appropriately and remember that brakes are used in both directions.
When the assembly is mounted on the disc, the forces should ideally be tangential to the centre of pressure of the pads during normal braking. This can be used to minimise frame distortion and to maximum braking advantage on ultra light designs.
Holding the brake in position with a rubber band around the handlebar lever will help hold the assembly in the best position while fitting and welding. Preferably use new pads and ensure the alignment either side of the disc is perfect - by checking with worn pads too.

On rear drive or two wheel drive systems, the brakes can often be inboard, with forces transferred via the transmission to reduce wheel mass, and often offsetting the extra mass of the drive mechanism. Where intermediate shafts or other drive devices are used in such designs, they may compromise the brake feedback, but can also reduce fierceness in the brake system.
If hybrid engines become popular, energy generating brakes may become popular, and if electric, can be adapted in many ways to ensure energy generated is energy used productively. More details in later monographs if funding permits.

The uncommon use of a gearbox output shaft mounted disc is that a smaller item can be used, as the gearing ratios are often 1 to 3 front to rear sprockets, so the front turns three times faster, requiring less force. Although heating can be a problem, so air ducting cooling should be considered fully to prevent damage to the attendant components. This option also reduces the unsprung mass on the rear axle.

Master cylinders.
Hydraulic brakes require a specific positioning of master cylinders for fundamental hydraulic fluid reasons. If the handlebars are positioned for perfect comfort, but the master cylinders cannot align correctly, then they must be replaced with alternative master cylinder designs available from custom machines. Where simple alternatives are not possible, then use a remote reservoir design. Other options include use of a cable, to mount the master cylinder inboard, under the tank, or elsewhere on the handlebars or other modifications.

When making special brakes, the relative bores of master and slave cylinders need not be completely exact, as the brake lever pivot can adjust the lever ratios to refine the overall pressures needed for ideal braking in most conditions. It's all a matter of transferring a force from one place to another in a manner most appropriate to the purpose. Many master cylinders are often available in three bore sizes.
If the master cylinder is at an unusual angle but not a radical angle, then a filler cap extension can be designed to offer a new fluid level above the master cylinder vent holes and allow a new filler point. When bleeding the system, the master cylinder may need to be positioned in a more normal alignment unless new vent holes are drilled. The old holes need not be filled.

By liberating the brake levers from direct connection, the master cylinders can be mounted anywhere they are out of the way and remotely operated by cables or tie rods. This is standard practice on some German and on many minimalist looking custom machines for cleaner lines. Positions may be below the handlebars for close, minimal connections or perhaps inboard for clean lines. Cables are possible, but tie rods are better as they are unlikely to distort thus maintaining better feedback from the brakes.
When mounting remotely, the master cylinder actuating lever can be replaced by a similar piece of alloy sheet, carved and fitted with eccentric pivot to allow different tie rod ratios to help refine the control harmony. Alternatively the original lever may also be modified to take a cable or linkage for easier spares compatibility. To actuate a remote master cylinder, it should be mounted so that it's lever can be pulled by a tie rod acting in a minimalist manner. A master cylinder lever should contain a threaded adjuster for adjustment of the bite point.
Mounting the master cylinders on the handlebars will help as extra mass to reduce handlebar vibration from some engines. There are very few two wheeled machines which demand the lightest possible steering mass. (Some well known top of the range touring machines have been known to have the manufacturer mount a solid iron block under the bottom steering yoke as standard. Yuk.)

Linked braking is often less than well appreciated, being either a fixed design by the manufacturer, or a cobbled together design without adjustment. It is not difficult to see why such brakes are often ridiculed, - even when expertly made by large manufacturers.
Simple braking application from a single lever is an ideal, but only if it can be set up for personal preference and the road conditions.
Ideally a braking system should be able to sense and adapt to the axle loading, such as having passenger or not, and if the weather is wet.
Anti lock braking is for the oft common real world scenarios where inaccurate braking skills, unknown road variables or poor feedback are to be expected. Integrating antilock braking will require wheel sensors and servos, which in turn need good power supplies.

The following is a simple yet effective design to see if the builder wishes to reconsider linked braking for a particular design. Never try to link braking with other components such as electronic gearchanges until all other parts of the primary design have been fettled and proven reliable and safe.
For the simplest, yet effective linked braking with cables, a linked cable dual braking from one lever is possible using a swingle tree. A swingle tree is a cross piece for an equal pull on two horses when ploughing a field. (See appropriate text books. - Any farming text from the Middle Ages onwards should suffice.)
The basic principle is equally valid for linked braking on modern vehicles and systems. More so, as it can be adjusted for a proportional load on front and rear brakes. Yet even more so, as by using cables, one of the brakes can be also independently incorporated into this design without an extra third brake being needed, therefore two independent braking systems remain, but one acts on both brakes. This is applicable for any cable brake or a hydraulic system with the master cylinder force applied by cable.
For cable and hydraulic brakes, the swingle tree is best employed by a direct action on front and rear master cylinders when positioned close together. This allows easy adjustment of front to rear braking bias, even while riding, so that even this simple system can be adaptive.
The picture shows a Formula One car swingle tree.
The basic set-up uses a linked bar between the front and rear master cylinders, acting on the pistons. The pull on this lever is offset, with a bias for the front brake and should always be adjustable. The rear brake should also have a secondary, independent action on the rear master cylinder end of the lever.
NEVER use linked hydraulic braking unless a second, separate brake system is also employed.
As shown opposite, Formula One now use a similar system which is adjustable from the cockpit. The system has the brake pedal pushing against the front and rear master cylinders, with a central link which can be offset. The F1 design is poor and uses a primitive adjustable pivot, rather than a proportionally adjustable movements which would be far more subtle.

There are many variations on this theme which can be used to assess this concept.

Wheels.

There are two basic wheel hub designs, either to build a simple steel hub with twin bearings, similar to a steering head or to modify or re-engineer a bike or car hub.
Apart from wire spoke designs, there are many other basic wheel hub to rim support designs. These include carved from a single sheet, modified car, or a set of identical, separate sheet or tubular spokes welded to a dedicated hub or a mounting flange.
As mentioned earlier, building a hub is similar to a steering head, although the rear will need a brake and cush drive or other form of sprocket mount. If ball races are used, make the inner hub spacer and the spindle spacers at the same time to ensure both have identical lengths for use with standard ball races. For shaft designs, try to keep as many standard components as possible.

The standard car steel rim can be removed by drilling out the large spot welds and reprofiling the centre to run true to the new bike rim.
My normal sequence for custom wheels is to build the hub, mount it in the machine, then spin to allow the sprocket to fit accurately. Then the brake calliper is minted to clear the three metal spokes and the disc mounted accordingly. Then the whole is assembled fully, welded, then the engine can be used to dress and test the assembly prior to fitting a perfectly aligned steel or alloy wheel rim prior to final welding.

If jigs are not used or available, the hub can be built up and assembled in position on the axle for accuracy. Jigs are second best to building on the actual bearings and axle while in the machine. Building the wheel in the machine allows more accurate alignment in the frame.
Consider re-engineering other steel wheel centres. Modify and trim them to suit the lighter loads and new rim profile.
New wheels centres can be built up using spokes made from sheet or tubular steel and fitted accurately to the hub.

If a car centre is used, it is usually via three or four conical faced nuts on studs, following car technology. Two studs is dangerous, five is often overkill. You can change a four stud to three or five if needed, then grind down the excess metal. Car wheel studs are often press fitted from the back of the flange. Positioning the wheel mounting stud on a new flange is difficult without an indexing head, so machine a small groove in the hub for the pitch circle diameter to ensure the studs are perfectly aligned. Then weld and machine small alignment pips so the wheel will align centrally on the hub, and use an old wheel to mark the stud spacing. For three studs, simply use dividers set at the radius of the groove to mark six points around the circle. Always dish or countersink the areas where the nuts will fit for better alignment. Then spin the axle with wheel centre to mark in the various bends, folds and other features, which can then be positioned perfectly concentric to the rest of the system.
Where an indexing head is normally required to drill holes, simply fit a perforated disc brake with suitable hole spacing, then make an alignment peg in an old or modified brake pad to give a wide selection of possible alignment points. The drilling jig can be a simple plate, tack welded to the swing arm.

Always mount the axles in position on the swing arm and frame, then accurately align to the centreline before machining to add the spokes, rim, brake and drive sprocket flanges.
Ensure there is adequate room for the brake and that the rear assembly is easily dismantled for maintenance and repair.
When assembled, a car hub used for a bike, can then be ground down to about half its original weight without loosing too much strength.

When building and aligning separate sheet steel spokes from new, balance is important, so always mark out the degrees of equal spacing to ensure accurate centre lines, to which a cardboard profile can be applied and drawn around to ensure even weight and thus better balance. Clamp them together and trim as a matched set. For example, if making three spoke wheel from sheet spokes, it may be preferable to mark the centre of each spoke and clamp them together in the vice before filing the 120 degree abutments. Then they will more easily fit evenly around the hub. If all spokes are made as matched sets, then when they are tack welded on the hub, they will balance evenly, reducing any positional imbalance.

If making from separate sheets, consider using a butted, stepped or overlapping design of spoke to improve both strength and alignment. See also Honda Comstar (TM) wheels. Align any steps to improve braking load resolution and to assist accurate alignment.
Fit the rim firmly on the spokes and turn until running true, then tack weld and double check. If the rim is slightly heavier on one side when the valve fitted, then it should be rotated on the rim until the whole balances well, so minimal wheel weights will be needed.

If spokes need some depth in cross section for more rigidity, (such as for extreme offset for hubcentre steering or single sided live rear axles,) then such spokes will need ribs or flanges. These can be made by panel beating grooves along the centres of the spokes. Use a leather covered sand bag, or make profiles in the end grain of a wood block, (prevented from splitting with a Jubilee(TM) clip), then use a ball pein hammer. Alternatively, the edges of the spokes can be flanged inwards to create ribs, similar to early Honda Comstar(TM) wheels. Cutting suitably shaped lightening holes in wide spokes will allow the edges of the holes to be flanged as well for extra rigidity.

For alloy rims, welding to alloy wheel centres will require argon or TIG welding, so some form of retainment for aligning is needed before sending to a professional welder. Temporary use of small self tapping screws can be used, allowing them to be removed after welding. Make sure their holes are also welded for use with tubeless tyres. Aircraft adhesives are possible but can be problematic unless a good interference fit is used with suitably strong components. Do not use adhesives if welding.
Reconstructing alloy car wheels is also possible.

If a hub centre design is employed, always build the hub unit and steering pivot first, so the steering axis can be used to align the rim to sit perfectly on the steering centreline to help perfect the steering.

The simplest way for a rear wheel, is to set the outer rim as the designed reference with offset from the centreline using a standard bike rim as a centreline and profile gauge. Then carefully set up and run the rim on a driven wheel. I use the engine, frame and rear swing arm as my 'lathe'. Make up a cutting framework to act as a lathe by welding a couple of brackets to the swing arm makes for a reasonably good lathe, powered by the engine. Use the engine on a fast tickover and the gearbox to adjust the cutting speed. Mount a cutting tool such as a broken off hacksaw blade, very securely fixed to a long broom handle, use goggles, and use this on a lever system to gradually cut away the other rim. If done carefully, then the rim may be removed in such as way as not to damage the main wheel structure. You may experience 'chattering' caused by the light mass of the wheel and inappropriate cutting. Do not use a high speeds, as the rim will already have a high cutting speed. Wrapping a heavy mass around the tool or rim may help, such as many wet rags, or use your spare hand to dampen the rim using a wet rag. Adjust the speed and depth of cut and angle of the cutting edge until you get a neat cut. You will probably have four alloy wheels to play with, so start with the worst wheel until proficient. Done neatly, the removed rim can be moved closer to the inner rim and then be welded after preheating. If very neat and a small bike, it can be bonded using aircraft adhesive and a few 'chicken screws'. Use the original bike rim profile to make a mounting gauge for excellent accuracy to the new rim. Ideal for hub centre steering designs. More details you know where by now.

Fuel system.

Mounting fuel tanks is important, as both empty and full fuel tanks will vibrate at different frequencies. Fully loaded fuel tanks react strongly to braking, so use anti slosh baffles or alloy honeycomb on long tanks. Always ensure the welds on a fuel tank are positioned such that they will not fracture. Vibration mounting and damping of a fully loaded fuel tank should be such that it will minimise fracturing of any part which is prone to vibration, such as long, unsupported sheet sides. The use of internal bracing, integrated ridging, compound curves and many other techniques are available. Composite carbon/aramid/alloy honeycomb fuel tanks are mentioned in a companion monograph.

Fuel mass distribution may be very important for optimising the handling, dependant upon the capacity. If using heavy fuel loads, such as endurance racing or touring, then the fuel should be ideally centrally placed to maintain overall balance. This can be accomplished by centrally mounting the fuel tank evenly between the axles. It is also possible to use forward and rear mounted tanks which empty evenly, in stages or proportionally to maintain balance. The traditional 'tank' in a dummy form, may be used to house components normally positioned under the seat, especially if weight balance needs adjusting.
Where extra fuel is required but cannot be balanced, it may be possible for the most upsetting volume of fuel to be consumed first, probably with dual cells or tanks, so the bike returns to optimum balance as early as possible.

Underslung or low fuel tanks keep the mass low and can often be placed in a perfectly neutral manner. Some designers may say the exhaust should be under the engine and the fuel above. Others would argue that a heavy mass should be low, with light components such as 'empty' tubes, higher. See also Mead and Tomkinson's 'Nessie'.

As underslung fuel tanks are often long and thin, they should contain baffles or alloy honeycomb to prevent sloshing. The not uncommon practice of underslung fuel tanks can take advantage of the often standard car practice of a 'hammock' support system.
Where a fuel tank can separate easily from a machine during a crash, always ensure the fittings will leave a tank with the pipes sealed, so fuel spillage is prevented. This often means using a vacuum fuel tap, or simply an integral fuel pump whose wiring and fuel output pipe disconnect safely in a crash, which is the method I prefer.

Underslung tanks require fuel pumps. Car or bike types of fuel pumps are usable for carburettor machines. The pumps are in two types, low and high pressure, 3psi and 6psi. (psi = Pounds per square inch.) Low pressure is for mounting close to the carb, whereas the higher pressure, (6psi) is for cars where the pump is close to the fuel tank at the rear, with the engine at the front, much further away. Most bikes will use the low pressure type.
Fuel injection systems use different, very high pressure fuel pumps.

For traditional carburettor motorcycle fuel systems, a reasonable height difference (head) between bottom of fuel tank and carburettor float level must be ensured. This need not be much, but must ensure adequate pressure difference for the restrictions of fuel filter and the fuel float valves.
In unusual machines, it may be necessary to use a small header tank. If not connecting the pump directly to the carburettor, then such a header tank is required. This should maintain a reasonable height (head) above the carburettor and maintain the level with an overflow back to the fuel tank. With header tanks, the solenoid type of fuel pump will want to over-pump constantly, so a restrictor should be used, capable of being adjusted to supply fuel at just a little more than constant full throttle requirements. If a restrictor is not desired, then a very basic header tank can use a modified two stroke oil tank with a low oil level warning switch to control the fuel pump via a relay.

Fuel injection systems use dedicated pumps which work at higher pressures, around six atmospheres (90 psi) and include high pressure filters etc. Always use the original equipment if in doubt. Always fit a high pressure fuel filter before the injectors, where the orifices can be very fine. Fuel filters are cheap insurance.
Some fuel injection pumps are electric impeller motors running unsealed, directly in the fuel, so always fit as found and always include a tilt crash sensor to stop the pump if the bike should fall over.

Problems with exhaust system heat and fuel tanks can be constrained by integrating an air barrier between the fuel container and the exhaust. This should use an insulated heat barrier and further improved by airflow. As some heat shields tend to vibrate loose, they should be incapable of damaging the fuel tank, yet be fail safe should their mountings fail. Double heat shielding is preferred, one on the exhaust to minimise radiation and improve air flow, with a second as an insulation barrier glued to the fuel tank.

Oil tanks.
Oil tanks are often as used by the original machine, although the shape can vary to match the new design. The return flow inlet pipe being positioned to check flow when looking into the filler cap and the outlet pipe having a wire mesh screen which can be cleaned.

Two stroke oil tanks are not big, so can be built into the frame tubes. Likewise four stoke oil tanks can be in the frame for extra cooling and weight reduction.

The frame can be used for the oil tank. Use a good welder but do not position any connecting pipes where they can encourage fractures to occur. Drill adjoining holes for both oil drain and air venting between the connecting frame tubes before welding and always have an oil filter after the frame outlet and definitely before the engine. Four stroke oil holes in the frame tubes must be large enough for maximum oil flow at top revs, otherwise oil starvation will occur. Make sure all the oil will drain out. A simple vented cap from a moped two stroke oil tank will suffice for filling and venting, if hidden from sticky fingers. Never take the oil feed from the bottom of the tank / frame, always allow an area for unwanted sediment to settle, with the oil pipe a little higher, preferably with a wire mesh screen.
If a two stroke oil tank, then always have the bottom level or just above the oil pump intake, when the machine is vertical and when on the side stand.
Knock any weld slag free as the frame is constructed and use mechanical methods, and if necessary use acid to clean out the inside of the frame. Slag is not dissolved easily by acid. Partially filling a frame with grit and water, then sloshing it about good half an hour will clean out most debris, then fully flush at all angles then fit a good fuel or oil filter at the frame exit. Alternatively, take the frame to a commercial acid bath cleaner.

If a two stroke oil tank, always fit a low level warning system.

Where oil level cannot be assessed by a dip stick, then the oil level can be seen via small tubes above and below the level, connected by a clear plastic tube. If welding small pipes is difficult, simply push the pipe in a small hole in a safe part of the frame, below the intended oil level. To save bends in the small pipe, place a steel spike or rod in the frame tube hole and lever the hole so the pipe is fairly vertical and then solder it in place. Then run a drill though the tube to check oil access.
For two and four stroke tanks, add a small red floating ball and make sure the pipe shows a low level.
For four strokes, the pipe can be high and used purely to show the upper level.
For safety reasons, any oil level sight pipe must not be allowed to drain from a broken pipe, so this should not be too far below the desired oil level, but low enough to see when filling up. To protect the pipe, the clear plastic tube can be protected along its whole length with strong sleeving, with just the oil level area exposed for inspection. Alternatively a second, larger bore clear pipe can also be employed to protect the smaller oil level pipe.
The pipe can then be run along the frame tube to be vented into the oil cap. Never use a level pipe as a vent, as it will simply overflow should unwanted pressure build up.
Oil in the frame can show up any fractures at an early stage and can be considered a safety feature rather than a problem.

There are various techniques for welding pipes in frames. Bronze welding is better for strength and ideal for reducing fracture points of small tubes and fittings. Very lightly loaded fittings such as oil level pipe can be heavily soldered. Mig or Tig welding will leave the frame with minimal internal slag which could flake off and clog the oil lines. Always clean the insides of the tubes before final assembly and welding. Where welds are to occur in the frame tubes, clean back to bare metal prior to tig or mig welding to minimise internal slag. Follow up with regular inspection of the outlet pipe to check for any clogging and use a sediment trap which can be cleaned out. In a few designs, it is possible to put a handful of coarse sand and water, then shake the inside of the tubes to clean out any light corrosion or flaking caused by welding. Fully pressure wash clean afterwards.

Cooling.
Never mount a radiator directly on the frame. Where possible, use a rubber mounting. Support the unit to prevent it sagging through the rubber which may also eventually cause vibration in the mounting. Therefore compressive rubber base mountings are preferred.
Where possible, position the exhaust, radiator and frame in a manner that they need not interfere with each other. Directing the airflow will help when moving, but static running can compound poor cooling problems. Slow moving machines produce little heat, but even this heat must not be allowed to build up, so fans are a must if the radiator is hidden from airflow in static conditions. If the radiator is horizontal, natural convection can help in still air.
Radiator airflow can change with speeds if not in a clean airflow.
Fans can be controlled by a temperature sensitive switch, common on cars and needing little in the way of wiring. Always have the fan supply disconnected by the ignition switch if using small capacity batteries, as fans that can run after the machine is switched off are prone to trouble.

On air-cooled machines which are enclosed, simply use car cooling fans connected to a temperature sensor mounted on the rear engine cooling fins. This can be adjusted until the best position for optimum cooling is attained. Car temperature sensors will need physical contact with the engine fins, so always ensure the mounting does not include possible insulation. Always make it a metal to metal contact. To get the best settings, simply juggle the position on the engine and perhaps add insulation around the sensor for best overall heat sensing for fan control. If unable to measure the engine running temperature, use a thermal sensor or thermal strip or measure the engine oil temperature of a standard bike after a run, and the new machine after it has been running for a similar length of time. Then use a remote temperature sensor in the engine oil for initial long term running to gauge the overall engine temperature, and thence to ensure the engine does not overheat.

Exhaust.
Standard exhaust lengths should be retained unless for a good reason. Lighter racing exhausts often have thin walls and transfer their heat much sooner along their path. Maintaining a cool design is important, so routing of exhausts is important for safety and comfort. All exhausts should have adequate cooling airflow around their whole length. Careful heat shielding should be considered in tight areas.
Some experts say the exhaust lagging will improve performance, but a cooled exhaust will reduce the density of the exhaust gasses, decreasing the exhaust valve pressure, helping thermal efficiency. Lagging is only needed if the exhaust is not safely cooled by airflow.
Rubber mounted engines will need the headers and mid part of the exhaust to be mounted to the engine components to prevent fractures and to be rubber mounted near the rear of the frame. Where the exhaust flexes, should be near an engine mount to minimise flexing and subsequent fatigue.

Mudguards.
It is often much easier and cheaper to buy and modify a mudguard than build one.
If panel beating a special mudguard from sheet steel or alloy, always include a crimped edge for safety, extra strength and to reduce fracturing.

Fairing / belllypans.
As aerodynamics of radiator airflow is paramount, the use of temporary cardboard and Duct (gaffer) tape designs should be employed and modified until a clean, reliable airflow is possible. See also aerodynamics later. Once a decent design is built, it should be smoothed and a mould taken. A composite item can then be moulded, usually in glass or carbon reinforced plastic.
A lot of development went into the JP7 belly pan, to allow the two slanted radiators to have suitable cooling airflow as a high speed touring machine, and remain cool in static air in traffic jams in Taxi bike mode. The hugger rear in this example is part of the external airflow extraction, where I'm encouraging the natural low pressure zone to help extract heat from the engine bay.

Stands.
Not all machines are built for speed, some motorcycles are built to tour where a centre stand is an excellent tool in its own right. Always make sure that removing one wheel will allow the machine to rock onto the other wheel. A gentle rocking base with a cam foot profile can assist the rider to lift the machine more easily onto the stand. Where the abrasion with the road is a problem, use rubber foot strips.
For enduro and ISDE machines, a variation on two side stands can be employed, although optimising the design of the bike so the wheel can be easily removed while laid on its side will save more weight.

Tool kit.
Always carry a tool kit when testing. Carrying a tool kit on the person is dangerous, so always carry the tool kit in a secure pouch or container on the frame. Tool kit when testing is always larger than for normal use, so make the container accordingly, or use an extra tool bag. Always Include a first aid kit and cell phone.
Only Italian scooters have managed to carry the ultimate spare components, a spare wheel. For machines with fairly identical front and rear rim mounting, a spare tyre and rim need not consume too much room if integrated into the machine in a cunning manner.

Wiring.
See A Builders Guide to Bike and Trike wiring, available from this website at www.btinternet.com/~jhpart/index.htm
Most initial test runs are done with lash-up wiring looms, the minimal needed for testing the engine and any fuel pumps. fuel injection systems and just completely necessary items.
Always add a kill switch, even if it's only a wrist cord to a part of the wiring loom supplying power to the ignition coil(s) such that it pulls off easily in a crash. This is best done with a simple electrical connector in the power line and placed close to the riders wrist such that it easily breaks. Always make sure the live end is shielded to prevent shorts.

When making up even the most primitive wiring looms, always use separate fuses for important circuits.

When making the final loom, access to the electrics such as fuses and replacement or repair of fuel pumps, battery and spark plugs should always be straightforward. Always make access easy, even on a dark night, and include spare fuses and a small torch (flashlight) with a separate long life battery.

If using components which are relative to the safety of the rider, always overspecify the component, (but never the fuse rating) so that failure is unlikely.
Where suspension is controlled by electronics, such as vibration, weight or other sensors, always try to make the system fail to a safe position, or that the worst fault will not prevent the rider from coming safely to a halt.
Where stabilisers are used for enclosed machines, consider dual circuits and components for safe redundancy. Then add a fail-safe tell-tale warning lights to show if a circuit has failed.
Always have a secondary method of use, as to allow the rider to stop safely, even if stabiliser circuits should fail.

Application of electronics to many aspects of the riding experience is increasingly common and not always welcome. Unfortunately the application of electronics to increasingly important components can be worrying. From passive radios to interactive fuel injection and cruise controls to the important safety areas of brakes, the careful design and use of fail safe systems is increasingly important.
If worried about fail safe, three or more identical control chips can be wired to the same inputs or preferably independent, but similar sensors. Where one sensor can be fitted, so can three. The outputs can then be wired to simple logic gate so that if one fails to match the reading of the other two, the others will override the faulty command and light a warning LED. Simpler, but essentially similar to the space shuttle system. Additional logic can be used to notify the problem via a warning LED or other device. A manual override is also advisable during testing.

Load carrying.
Passengers must be considered as an unsecured load, therefore the seat must ensure they have the best chance of security and comfort at all times.
The passenger and luggage are the main variable loads. See also seats and fuel above.
The shapes and structures of materials to enable a machine to carry a load are available in various flexible, semi flexible and rigid materials. Good design can allow much more integrated componentry for maximum luggage room, with subsequent minimal reduction of external bulkiness.
Single sided rear swing arms offer some of the best possible options to reassess the pannier. The area available will keep the load very low, also much closer to the centre line and with minimal external bulkiness which will aid airflow and prevent the luggage from obstructing the machine in tight traffic.

The traditional motorcycle has failed to learn to keep the luggage load low. Some after market racks and boxes are truly appalling. Neither is there any need to bungee luggage onto a machine in incoherent ways. Consider the ridiculous application of conventional modern motorcycle panniers, all too often with a top box mounted ridiculously high to give the worst possible handling. Some side panniers are ridiculously wide, occasionally scraping cars on both sides in city traffic. Fundamental luggage design has patently got worse with time.
Always encourage luggage placement which maintains axle loadings and aerodynamics within sensible parameters.

The builder may wish to position the heavier luggage components to keep centre of gravity low, while mounting lighter luggage higher. Start the design process with the ideal positions for individual luggage requirements until the optimum is created, then create panniers to contain them.
Positioning rigid panniers close to the machine can eliminate the need for mudguards and thus save weight and maximise room usage and possibly improve handling of a heavily loaded machine.- A large top box should be considered a design failure.

Look at the area around the machine. See it not as where things cannot go, but as everywhere luggage can fit. Apart from having cooling airflow and to put the feet down, all else is available in the area of design. It can also be seen as a means of minimising personal injury during a fall or crash. Do not disadvantage the aerodynamics, but take advantage of the situation to improve the aerodynamics and cooling air flow.
Luggage should also act as positive safety and aerodynamic devices, not as obstructions.

Long range fuel tanks as used on 'around the world' bikes are possible in any shape, flexible and / or rigid. Some 24hr racing motorcycles have underslung fuel tanks which show the possibilities available for carrying such loads. See also fuel, above.

On some machines, such as touring bikes or recumbents, the long gap between rider and any front luggage bag is not going to prevent damage in an accident, but anything soft between rider and impact zone such as car or wall should always be encouraged. Therefore, on some machines, even bikers can have an airbag, or at least a basic alternative. With or without a fairing, light articles such as sleeping bag are ideally placed high and over the front wheel or upper fork yoke, as this is an opportunity for aerodynamics and weight loading. The area between torso and any frontal objects should be viewed as a shock reduction zone, allowing the rider to decelerate before sliding over the offending item. Therefore it is but one more design step for careful design to allow crash protection to be applied where needed. Basic crash protection easily equates with sleeping bag and clothing in a soft luggage carrier or tank bag. Modern materials such as used on rucksacks are excellent for soft luggage, which can also be tailored to an aerodynamic and safe shape.
Airbags are compact and self contained, often needing only a simple acceleration sensor to work. They are only useful when the impacting rider squashes the bag against an impact surface. Make sure the sensor is correctly aligned. as the y often use a ball in a rap design for crashes from al possible directions. Ensure any airbag will be positioned between the rider and the impact zone, otherwise it is of little use. This area is very involved and will need further research if deciding to apply it to conventional motorcycles.

Luggage need not simply mean carrying passive, stored items. Interactive items such as the ubiquitous hands free, voice activated cell phone are now part of life and easily attached to a touring machine. Cup holder design is not the exclusive province of cars.
When fitting items in front of the rider, a suitable position should entail safety and the ability to use easily. Do not position anything so it will impale the rider, or at least contemplate use of easily sheared mountings.

For simple panniers, glass reinforced plastic is ideal. Think of the load, mounting, balance, contents, lighting, then carve dummy pannier profiles from white foam, as used for packaging TV's and fridges. Large sheets are available from most DIY centres. Carve to fit such that they will integrate positively with the machine, both in mass placement and aerodynamics. These foam shapes are the start of a vast variety of subtlety. When the shape is decided, carve strengthening grooves where needed into the foam pannier cores, cover with cling film, then mould these internal ribs first. Then mould aramid strengthening strips to secure the various mounting brackets before covering in final layers. If the foam melts with the resin used, prime it first with undercoat, plaster, cling film, cooking foil or parcel tape. The later makes removal easier. Carefully slice the opening to make the lid. Then with a motorised wire brush, spoon or electric kitchen knife, remove, dissolve or otherwise remove the foam. Make an inner lip in the lower opening so water will not get in and fit the hinges or simple internal bungees etc.
If the rear panniers are in left, right and top sections, the top could fit securely over the side panniers, to act as the lids, thus reducing weight while also adding rigidity. It can also make a good camping table to go with a removable recumbent seat for truly comfortable tour camping.

There is nothing in the text books to stop the design using the motorcycle itself as the luggage container. If built in a form similar to many scooters and mopeds from symmetrical stamped sheets, the whole of the centre of a box frame could be used. An opening in the area of lowest stress built up with a strengthening flange to take an access hatch. Only applicable for small engined machines.
(See also the extremely rare Turner Bivan, the ultimate motorcycle luggage carrier.)

The ability to add accessories ad infinitum does not always make a better machine.
Always follow the old adage of 'remove complexity and add reliability'.

Keeping it tidy.
This is the free dimension area, where art is the prevailing force, or where form follows function, or whatever the designer wishes.

You will know when it looks right.

No amount of writing can offer advice on personalised design. A great deal could be written concerning the smaller aspects of design, with some ideas offered in other sections.
Generally, the overall style must always be taken into account because all motorcycles should have a better appreciation by the public.
The freedom available with personal design allows the motorcycle form an immense range of opportunities for style without detriment of engineering excellence.

The best custom bikes are also superb works of art in their own right.

Testing.

Not everyone builds radical machines, but for those who do and even for those who build conventional customs from scratch, make sure you get the most from your first test ride.
Sometimes it's a wonderful experience, sometimes it's just plain frustrating, sometimes frightening as you learn to understand what may be going wrong or try to understand why.
Gradually you understand the machine and what is actually going on beneath you. Then you can take a wider view to assess all possible solutions and decide to test the more promising options. From this you will gradually solve all problems and perhaps even redesign small or major areas of the design. It's called continuing research.

Testing is either an attempt to destroy the machine to find its weakest areas, or to carefully build up confidence and take an almost paranoid attitude while pampering the machine during test riding. The choice is yours. Never allow the test riders safety to be a part of the testing procedure.

The first tests are the first rolling chassis in the workshop, as mentioned earlier, where the frame is given a hard time with the intention to find any primary structural weaknesses. Likewise the engine will be run to test the drive train, controls and rear brake.

Not all machines will be ideal.
Even the worlds best manufacturers make the occasional blooper. The vehicle industry is littered with vehicles best forgotten, not only by reputation, but also by serious basic design flaws. After an atrocious machine is built, a vastly better machine often appears next time around in the light of the excellent understanding from many design hurdles and pitfalls encountered. Only big manufacturers who make bloopers have failed to do their homework.

Occasionally, an impeccable machine is created.
Such machines may exhibit excellent handling, superb ergonomics or completely balanced control harmony and occasionally all three. Never destroy an impeccable machine, but allow others to test it to understand why it's so good.

Just knowing it's perfect is not enough ! - always take the opportunity to understand the fundamentals and subtleties from other points of view, so nothing is missed from such opportunities.
As in the JP series, a good 'blind' test is to get complete learners to learn to ride on radical machines, as learners have minimal preconceived ideas or preferences concerning handling or ergonomics. Their feedback is priceless.
Never allow a learner to ride a less than excellent machine.

An embarrassing admission is that some machines 'thrown together' to quickly test an aspect of a design have also turned out to be outstanding machines :) It happens more often than you would imagine.

If not completely happy with the first attempt, possibly because manufacture is not superb, or the ergonomics are unsuitable, it simply does not handle well enough or a host of other reasons, do not despair. Always fully test ride it anyway and understand where the problems are, as bad machines can often highlight what to steer clear of. Only then should destructive testing be considered, possibly with the intention of a partial or total rebuild.

Much more can often be learnt from an imperfect machine than from a perfect machine.

Although much has been offered for the design process, it may be better to make a temporary machine to test the form and allow modifications prior to the final form. In some cases, a very radical machine should be roughly built in steel and modified to get the geometry and suspension correct or close before investing in a refined manufacturing process such as a bronze welded ultra light space frame using expensive lightweight tubing (as shown right) or composites. The LE Velocette had a bolt on steering head, while the 350cc Velocette had adjustable rear shock mountings. There is a vast array of highly adaptable test designs which have been used. Use to best effect. See also Phil Irvings book.

Test riding.

The very first test ride has no constraints other than to ride cautiously and with an open mind.

No preconceived ideas, other than to be safe. To leave the mind to openly and freely assess the machine as a new design.

The first test ride is vitally important.
You must carefully asses you initial reactions, because after this, you will have already started to adapt your mind-set and riding reactions to the machine and it is vitally important to take note of your initial reactions. This is even more important on radical machines. The reactions and subjective assessments are then written down in a notebook for the machine.
I have many notebooks. They make very interesting reading.

After test riding far too many new and radical machines and custom bikes to remember, my testing still and will always done with a pencil. This is not bureaucracy, it is fundamentally important knowledge which is all too easily forgotten in the ensuing months.

(For example, the JP3 first test run was strange, simply because it was a recumbent with hub centre steering with single sided front and rear suspension, and a shallow squab rake.
The chassis was set up for general purpose use, with moderate rather than soft shock settings, and the steering rake was on the safe side, with the trail adjusted a little more than needed. The brakes had been tested statically and proved adequate for slow speeds until they had bedded in.
Pulling away for the first time was no worse or wobblier than most other reasonable machines, but my notes bring attention to the low seat height with the handlebars under the seat being a possible problem in corners, but this proved to be no problem, even on twisty Dartmoor roads.
It was not the riding experience that was noted first, but the comfort and ease of use. Initially I had worries about the backrest causing lack of rider weight change, and that low speed stability may be a distinct problem. Quite the reverse - the machine handled better when the rider relaxed.
Gradually the steering rake and trail were reduced until it could be steered by the absolute minimal finger tip pressure on the handlebars and I could ride to a standstill with hands-off. The notes show that I later used the bang-bang technique (Albuquerque N.M.) to set up HCS in subsequent tests and find the widest handling parameters for rake, trail, anti dive and suspension set-ups.
The JP3a hand gear change was also a temporary lash up for testing, but turned out to be so nice to use and everyone liked it, that it has remained and is to be integrated into the JP8e as part of the ergonomics package.
Later, the JP3 had problems with the rear axle chain adjustment and a poor choice of front brake (found dumped in a local estuary) All but the front brake was gradually improved. I am still looking for a truly stunning front brake for the JP3, as in all other respects is ins now the best handling bike I have ever ridden - bar none. This machine was later test ridden by a young lad who had never ridden a motorcycle and a few female friends and a few French guys who had chased me across Bordeaux.
Because I was never really happy with the various parts of the design, later machines had better front brakes and total rethink of chain adjustment. A JP3f may be made in composites as it remains my favourite design. The JP8 is now the successor, with a composite frame and superb brakes. )

I always start all test sessions with a list.
The list consists of what is needed to be checked before anything else.

I always leave the test session with a list.
The list consists of initial subjective assessments and feeling on the design.
The list also includes what went wrong, or needs changing next time, such as sloppy gearchange, stiff steering to one side or brake imbalance, or any of a host of possibilities.
The list also includes many ways to improve the design and refine the design, and also to push the design further.

For the second test, the list once again begins with what is needed to be carefully checked before anything else.

I consider a notebook and pencil as truly vital parts of any testing programme.

TIP: The first test gives you a major opportunity which will soon disappear. - The first ride will have no reference points and you will be assessing the way the machine behaves in a raw, untainted manner. As more tests are done, you will naturally adapt to the bikes peculiarities and thus loose totally subjective assessment. - You WILL get used to and adapt to the machine and its foibles. So from the outset, set very high standards and always be critical, so that your assessment does not become devalued with familiarity.
All too soon during testing, you WILL soon adapt to a slight imbalance, a slight unevenness in the handlebars, less than ideal brakes, less than ideal low speed stability and many other things which will soon disappear into 'adaptive riding', and these must be noticed and noted early, as part of the testing schedule.

Therefore the first ride should be simple: Pull away to see how the engine clutch and gearing behaves, ability to find the footrests, then a straight line for balance and possibly hands off or at least light feel on the handlebars, then a gentle turn, to see how it reacts to rider input.
Then back and stop. Just sit and think.

On a very radical bike, you may be grinning.
But also thinking - 'great in places, but what the hell was it doing when such and such happened"?

If all is well, then testing can continue.
If you did not do enough work in the workshop, you may be returning to sort out the broken brake lug, useless clutch, sloppy steering linkage or anything else which should have been checked before going to the test site. Too many poor and dangerous machines are used on the road.
Never allow a less than competent machine out for testing. No excuses.

The first test ride must also concern safety: mainly structural strength and the brakes.
All cables, bearings and brakes settle and will require adjustment. Once the machine holds together and the brakes work, the study of the handling can begin. It is for this reason that most safety testing must be done in the workshop, to ensure all has bedded down well enough and checked out so that handling and general ride and feel of the machine can be studied from the outset.
There is nothing worse than getting to the test site, only to find the gears do not work or are not the correct way around !

Always make the first test run one of dual use - safety and initial rider response.

ALWAYS write down all initial reactions and opinions after just one minute of riding. Anything more than this and you will loose the primary subjectivity. This is particularly important on radical machines which have no references to other bikes. (Hence the recommendation to try gliders, wetbikes and such like, to help refine your responses and decide if they are positive or not.)

If needed, try using differing or unusual tyre dimensions and profiles, their pressures may be even more important than normal. Start by noticing tyre deformation on standard load. Then begin experimenting with pressures to get a matching deformation pattern. Try to steer clear of maximum rated tyre pressures and be prepared to aim for a sensible and balanced set of pressures. (Getting the weight balance correct on bathroom scales will eliminate tyre and many other such problems.)

Learning the braking characteristics in a quiet area will be advantageous for knowing the basic limits. This will help the adjustment of the braking system by modifying and refining lever ratios and pressures for best use. It is very easy to build a machine with misbalanced front and rear brakes, yet fairly easy to cure. Choice of pads, reduction of braking material, lever ratios and many other methods can lead to matched brakes which can be a pleasure to use, and brakes save lives.

All machines must brake in a straight line with hands off.
Once the machine is stable, use a small temporary, frame mounted handlebar section with throttle and front brake while checking the hands off braking tests. Alternatively apply the brakes with finger and thumb, with the riders arm positioned vertically, (with the elbow awkwardly but neutrally positioned above the right hand ) so the rider exerts absolutely minimal control on the handlebars when applying the brake. Any pulling to one side when braking can be from frame or wheel misalignment or distortion under braking forces, rider placement and a host of other variables.
As mentioned earlier, where the braking is too efficient, the brake pads can be reduced by tapering, or stepping, lever ratios adjusted. Another trick is to fit a rubber section in the end of a bowden cable, to give a little cushion, or a small air bubble in a hydraulic design. Different lengths of rubber and bubble sizes will allow refinement. Adjusting the bubble size is an art. Neither will damage the main units and can be removed without damage if unsatisfactory and until the problem is sorted.
There is no excuse for inadequate or poor braking.

Use of a water patch and a gravel patch will help to understand how far the design can be pushed and to test how it looses control. Carry some water for any depressions in the car park, and a small bag of sand to make some impromptu testing areas.
If no kerbs, a rounded edged wooden strip held to the ground with blue tack (after brushing clean) will make adequate bump strip for straight and side angle kerb testing. An old door can give four different edges, plus two rumble strips along its length. One rumble strip to assess the suppleness of the suspension, the other to upset the chassis with bumps set relative to the wheelbase. Kerb tests are not suitable for delicate wheels, except for testing where replacements may be needed for road use.
If your machine cannot handle kerbs at speed, then it is not strong enough.
With smaller front wheels with light loads, the limits of the front wheel may need to be pushed, possibly trying to get it to break free in faster tight corners, with and without braking. Elbow pads, gloves and such like are recommended when finding the break away points during cornering. Skate boarding progeny are an excellent source of safety equipment.

I have a very large friend in security who likes sliding bikes down roads: Two of the JP series after standard testing, gave a fun afternoon sliding as far as possible to eventually assess comfort of recumbents when having such 'fun'. This is NOT recommended for conventional motorcycles.
The JP6 was slid sideways at speeds up to 60 mph and I walked away with grazes. - Always choose higher speed test roads with soft grassy verges and run-offs.

Important tests include the minimum turning circle and the fastest constant speed into a sharp turn such as a test version of a right angle street junction. The use of real or imaginary road cones, chalk to mark the ground and a big, quiet car park is ideal. A minimum cornering radius at a natural speed will soon be found, and should be recorded for comparison with other rakes and trails. Gradually decreasing circles will decide low speed handling and help decide low speed ground clearance measurement.
If you have hubcentre steering with adjustable rake and trail, or perhaps and adjustable upper fork yoke, then spend an hour or so simply turning 'figure of eight' circles to see how small a turning circle can be made with neutral effort, and at what speeds. Note the rake and trails and their effects. Adjust any variable geometry for minimum stable turn speed and then compare its stability at high speeds and braking. Then adjust for overall stability and personal preference of riding style and then finally adjust for reasonable stability at high speed. The compromise of high speed stability may need an old runway or quiet road, so the optimal balance between high and low speed handling can be optimised for best overall handling. A digital speedo and lots of chalk and a large, quiet carpark help refine low and mid speed stability and cornering.

As the subtleties of handling are gradually refined, there may often be a trade off between tighter cornering vs straight line stability. This can be adjusted to personal preference with adjustable trail, tyre pressures and rider placement. The final decision will depend upon use. A touring machine often turns less well, but with better stability, whereas a commuting machine will usually be set up for 'urban motocross'. Even a trials bike, set up to be incredibly nimble, should be surprisingly stable at its limited top speed.
A general comparison is where transport planes are usually stable, whereas modern air superiority fighter aircraft are designed intentionally to be partially unstable.
For low centre of gravity designs with hub centre steering, then both tight cornering and high speed stability are eminently possible in one machine, giving hands off stability at all speeds, yet with superb slaloming and 'urban motocross' ability.

Good basic tests includes riding with hands off at low speeds to find the lowest stable speed. If the machine wants to pull to one side when trying to balance hands-off, then the rider or the frame centre of gravity may not be perfectly central with the tyre contact patch of the machine. Misalignment can also cause other problems such as poor load distortion on single sided swing arm designs.

Centre lines are important. The wheels and centre of mass of the combined rider and machine should be on the same vertical plane when ridden. Using a plumbline or piece of weighted string and a large mirror will allow the rider/machine to be set up to ensure the trees are perfectly vertical when balanced. While ridden, the wheels must be vertical for perfect balance. This may seem obvious, but is surprisingly uncommon even on standard machines from big manufacturers.

Unlike a conventional machine, a recumbent rider cannot lean left or right and will not allow easy compensation of upper body position for imperfect design or manufacture, but as seen from the picture, any machine can be designed to be perfectly vertical and stable in a straight line if you carefully consider the design and its fundamental needs.
On standard bikes, adjusting the seat just a little sideways can often help, or initially a little padding to bring the rider mass into line. As mentioned earlier, this is best solved while static at an early stage of building before permanently fitting the seat design and placement.

Hands-off riding is easy for conventional cycles for many reasons, including the 'balancing a pole on a finger' principle. Whereas for recumbent designs, hands-off riding will be harder to manage, even more so if using a seat squab, hence the need for impeccable handling designs at all speeds.
Here the JP3 is pootling around at a walking pace. I have no ability to adjust my torso for balance due to the squab, and yet it is still very stable and also very responsive to cornering and stability without the need for using the handlebars. Control naturally increases with speed, so a the faster the bike, then easier it is to control without using the handlebars. With conventional bike, upper body movement is easy, whereas on a recumbent with seat backrest, the control is minimal. Therefore the JP3 shows that if a machine is nicely set up, then even a recumbent can be easily controlled down to an walking pace. If a recumbent can do it, then so should can other motorcycles.

The main requirement is still a good rider. On a truly well balanced machine, only the need to negotiate city traffic or high speed country lanes may require use of handlebars. Slight 'body English' is al that's needed to control many motorcycles, from the humble moped to a massive touring bike.

Always aim to refine the handling from the outset, which is always more important than finding the top speed.

The rake and trail are going to be under close study. Unfortunately, this will be overshadowed in the early tests by poor gearchanges, uneven brakes and a host of small, occasionally annoying little problems. So always try to eliminate these in the workshop from the outset, so that the absolute minimum distractions arise during initial testing.

From the first test ride and al subsequent rides, write down the most important aspects first. Decide if it is easy or bad to ride, on a scale of 1 to 10 for various aspects, such as slow speed, average speed, cornering, steering ergonomics, and general ergonomics.
Whether the brakes work well or gearchanges are good is fairly irrelevant at this stage, as they can be refined independently of understanding the fundamentals.

There are many problems lurking, ready to upset test sessions, so take an organised approach to eliminating them before the tests. The engine may overheat, so check this before testing. Try to make the engine overheat, so the fan works and any coolant flow is not compromised. Then check the transmission works, by pulling away up a steep plank in while in the workshop, so the clutch and low speed carburetion is proven to be working well. Also test the drive train and brakes and lots of other annoying problems which can be tested in the workshop well before the first testing session.

The above is low speed stuff. It is important, as getting to know the machine is fundamentally important, especially on radical designs. Gradual speed increases are made once the ride envelope and breakaway characteristics and the necessary correction reactions are found and developed in the water and sand pits.
Learn to walk first before you run.

A good machine should be able to be ridden first time by any rider. Unfortunately a new, and especially radical machines will need time to be refined. During this time, the rider will naturally and occasionally, unknowingly adapt to the machine. This gives less defined feedback, as it is only natural for the rider to adjust the riding skills to match the machine. This must be realised and carefully assessed, to prevent undue rider adaptations which overcome unwanted variables in the design. This is best compared by back to back riding with a 'standard' machine, one which is generic and with general ball park handling for the useage and engine power. Having a similar capacity standard machine for back to back comparisons will highlight many basic and subtle differences.

Starting and pulling away for the first time may cause the rider to assume the machine will ride in a standard manner. This can cause the rider to under or overcompensate, and generally to wobble for a while. Feet down riding, until in a straight line may be required for poorly designed machines, or if the machine has not been refined to a general handling standard. The first straight line then gradually becomes a turn and a general feel of the unrefined attributes can be coped with until a few circuits are made, gradually applying more involved cornering and braking.

To repeat, once the first ride is accomplished, it must be analysed carefully, as this is the time when ordinary standards are still comparable with the new machine. Consider the differences at leisure, as thinking is just as important as riding. Write down your thoughts immediately. Writing helps to focus on the problems and how they interact with one another, and thus to refine the whole as well as the details.

As many problems as can be found, they should be written up for future reference. This is usually followed by a series of modifications followed by further test sessions.
When the tester has eventually decided whether the machine handles poorly and is unacceptable, then it may be preferred to rebuild the frame until it handles well. From this, a final design can be built.

In extreme cases where just the steering is not ideal, the builder may wish to mount the upper yoke with an adjustable central hole, or if desperate, to mount the whole steering head in a pivot so rake angle can be adjusted until ideal, until a final form of the machine can be built if required. Do not assume the rake angle is the main culprit of a poor handling machine, as a surprising amount of rakes can be applied on otherwise identical machines. Carefully check the trail, even though it is often difficult to measure on a adjustable machine. At least adjust the trail and note the ideal amount of trail. Always test with all other variables where possible such as adjusting the fork leg offset angle to adjust the trail, by variations on the upper fork yoke.
For temporary low speed testing, adjustable rake using slightly flexible bottom yoke and an adjustable top yoke can be employed prior to making a permanent set of yokes.

Usually the first test ride will be a case of sorting out small, annoying problems such as settling the wheel and steering bearings, gearchanges and seating support tension. Most, but not all can be sorted before testing in the workshop. For initial designs, especially from beginners, usually the main problems are a duff clutch or inability to find neutral and similar silly problems which should always be sorted out weeks before. Always use the rear brake tests to check the engine and transmission at an early stage in the building sequence.

Eventually the problems will be sorted or ameliorated and the optimal set up achieved. This may not be ideal for the purpose and more redesign and building work may be needed over the following weeks.
Even when building many customs a month, always leave the final machines alone for a week, then test them with many other riders and against a standard bike to ensure they do indeed handle well, and not by familiarity of an individual design.

Once a good handling machine is achieved, very accurately measure the axle loadings, rake, trail, axle offset and axle loadings, rider position, steering ratios, tyre pressures and whatever else can be measured. This is priceless information and will help develop 20/20 hindsight. It may often form the basis of the next machine.
During the refining process, again for future reference, write careful and studied descriptions of the effects of each variable at slow, medium and high speeds. Note the steering force, minimum 'hands off speed', any overt need of body balance, braking force, gearchange etc. Mark this information permanently on the main drawing and in notes. You now know why technical drawings have loads of notes and dates down one side of the sheet.

Road testing.
After the local large and empty car park has been used to check the basic design and shake down the components, road testing may begin.
The machine my well need to be taken to a ministry test centre to become road legal. so make sure it is a good handling machine.

Road testing is personal and depends upon the use and local areas. Places such as the authors preferred Dartmoor are ideal, with a wide selection of roads and a tourist free season. This offers few road users and a variety of demanding road conditions for pushing the boundaries, especially where there are excellent grassy run offs without hedges.
Suspension can be superbly tested on some bumpy back roads with off cambers and a mixture of bumps and dips.
Lightly hold the handlebars through a nasty section, to see just what exactly is happening at each sub assembly level. Do not be afraid to try and upset the machine by compromising tyre pressures, patterns and cross sections, and poor suspension settings.
Don't push it too far, just enough to see where it leads, and to give a general feeling of the ball-park conditions.

Where possible, choose three different downhill hairpin bends for testing at varying speeds, tyre pressures, brake and suspension set-ups. Preferably choose bends with good visibility, minimal use by other road users and large safety run offs. Always carry a first aid kit and a cellphone in case of a crash.

The JP series are regularly tested as fast as possible into various steep downhill hairpin bends, which not only checks handling, but also brake, suspension and control harmony. Similar for uphill into bends under power.
Making the machine as adjustable as possible from the outset will allow the test variables to be run many times in identical road conditions during an afternoons testing. The ability to adjust individual components, especially steering and suspension, helps to fully refine the machine.
This will gradually change from a machine which will do the job adequately, to one which is sheer bliss to ride.
Most custom machines are mere variations on standard themes. Making a radical machine to personal spec makes for a far superior enjoyment of riding. Riding fast along twisty roads, on an advanced, radical machine which is safe and reliable is great fun.

A few months building a machine should not be wasted by not bothering to refine it over a few months.
In the early stages, it may be necessary to rebuild whole sections of the chassis. Therefore it may be preferable to undertake initial low speed tests with partial welds for two reasons. The strength of the design is checked and second it is much easier to deconstruct and rebuild should major improvements be required.
For obvious safety reasons, some changes are only suitable for low and gentle speeds during initial testing.

There are many ways to assess a finalised machine, with testing against a standard machine on a race circuit, or a comparison with times for a standard machine across town or a test circuit. Perhaps if touring, a subjective rating of how interactive it is to ride compared to other machines in back to back testing. - If there is an open day with test bikes, always take the machine along for back to back tests and let others ride your machine. Also include testing by the dealer who may know his brand of machine well and would make a good comparator. There are many methods of assessment, with often a selection of various subjective and objective tests.

When building a series of machines with unusual attributes, then consider taping a check list on the machine along the lines of 'lowest wobble, drop into corner, minimum turning radius, antidive, steering pressures, relax'.
Being able to run through a set-piece check sequence will help to give better comparisons between tests. Relax is important, for if you cannot fully relax while riding the machine, then there is something very wrong with it.

Remember that ordinary standards are still applicable with the new machine. Consider them at leisure as thinking is just as important as riding, and write thoughts down immediately.

Unless a good machine is created, you should finally consider use of the machine to test riding to destruction. Many sub systems will survive for the MkII version, so make the most of any less then ideal machine.
Begin by riding over bumps, jumps and anything else it may encounter. Wear suitable protection from skateboarding progeny.

If in doubt about any aspect of the design, test, test, test. This is positive vandalism. If the machine remains complete, even after many modifications or bodges, then confidence is the first survivor.
If very brave, or wanting more information about a radical design, then final riding into a brick wall will highlight rider flight path, but always make it a low brick wall and have a few video recorders working to assess speeds and directions, as such things should never be done more than needed. A few bright spots on the rider joints will also help to measure the velocities. Always study accident problems such as neck damage, and have a friend with first aid experience standing by with a car and a neck brace to take you to hospital should something go wrong. During the JP programme, some machines were regularly crashed, with one heavyweight tester happily perfecting his technique of sliding the machines quite a long way on their sides in complete comfort.

All testing is dependant upon the purpose of the machine and safety of riders. First hand crash testing will always give much greater insights to the design needs and the possibilities which can lead to radical new ideas in crash design. Always be painstakingly careful when crash testing with real riders.
It is hoped that computer crash analysis will be made freely available to all vehicle builders as soon as possible. The testing authorities have been asked many times, so if reading this, please contact the author, as the safety of many test riders, including the author is directly affected.

If all is well, there may still be a complete machine to test.
Where breaks occur, reweld and prepare to test further if needed. The JP series are often tested initially with fifty percent welds to check the chassis.
After road testing, then the whole machine can be stripped, inspected, rebuilt and finished as required.

Static frame tests.
For those who wish to be a little more scientific, but wishing to shy clear of maths, then chassis deflections against load can be taken for future reference. The very last test is by loading to destruction. The headstock and many frame fittings are unlikely to be damaged, so can be salvaged later. Remove all expensive non structural components such as lights, carbs, disc brakes etc. Leave all structural parts in position to prevent the machine from distorting unnecessarily, including the engine and suspension. If a very expensive or delicate engine, then replace the engine with steel bars to structurally join up the engine mountings.
Where used, forks must be considered sacrificial and part of the testing procedure.

Choose somewhere quiet and safe with good lighting. This will allow the builder to see and hear cracks as they form. This is important, as this will help to discover the weakest points earlier. Always wear eye protection goggles. Final testing is accomplished by copying the fundamental loads in as found in use, but more so.

Torsion.
First clamp the rear wheel (or a spacer on the rear axle to mimic the wheel), clamped to the bench, a solid wall or jammed in a strong doorway with wood blocks and a car jack. Any use of a dummy axle spacer must be clamped so that the suspension arms are as strong as the original. Now apply a bar across the front fork yokes and measure deflections by gradually loading to twist the frame. Allow the bottom of the front wheel to slide sideways on a plank on rollers or marbles. Do not distort the frame too close to permanent failure of the structure - just look to see where the frame distorts the most, and why.
For a more basic test, hanging off the handlebars with your feet against the front axle will begin the process and give initial feel to where and how the whole torsion is acting across various parts of the machine.
To help recognise problems early, cover the frame in stretched fine tissue paper, glued across suspect surfaces or open areas or similar sections, possibly in little strips which will easily tear or distort. If the machine does not fail where expected, this also helps refine the design process by real experience. Listen for creaks and worse noises. Not all distortion may be in the frame.
Flexing the machine will help highlight the main distortion areas. Use of a digital camera in movie mode can also help, especially if set to record down each side, from above and from suitable angles. These can then be set to run as loops on a computer screen, and in some cases, magnified to comparison and measurement of the amounts of distortion.
Painting or gluing vertical data strips on the frame will enhance the ability to view deformations. Record the torsion deformation at various forces and at various positions along the frame. Where the torsion is most pronounced, record for comparison with other machines. Where a video recorder or a digital camera which can take sequences is available, position it for best viewing for later assessment, usually from the front and from above. Transferring video to computer allows a short video sequence to be run continuously so the distortion is easily assessed up and down the length of the chassis.
Single sided suspension systems may need mounting bars to fit the rear eccentric and the front axle mounting if not wanting to use expensive wheels. Always test by applying forces from the front and rear wheel rims or axles, otherwise the exercise is not highlighting all possible weak points.

Compression.
Because of the nature of a single track vehicle, most of the load is in compression. Unlike c car with heavy side loads, a motorcycle suffers very little side loading.
Only sidecar designs will need careful side loading tests.
If the wheels are not to be tested in compression tests, mount axle areas on blocks and allow one axle to slide, by placing on rollers under one axle, or on spare wheel bearings. This is to ensure the axles do not constrain the movement of the machine as it spreads under the load. If not testing the suspension as well, replace the suspension units with solid struts, so only the frame is tested, not the suspension. The struts should be about the average length of the partially compressed shock units and fork legs.
To limit and measure any gradual deformation, use an indicator and measuring device under the frame or sump, mounted on blocks. At the simplest level, a matchbox can be used, so the inner of the matchbox touches the bottom of the frame when extended. During flexing, the inner will be slid inside the matchbox and marked which can be read off at each stage, to help generate a graph. Use a matchbox with a stiff sliding action and mark movement with a fine pen. Masking tape or blue tack will keep the base in position. Anything larger than a matchbox will allow a machine to drop too far should it fail. The matchbox can then be recovered and the marks measured relative to the applied load to plot a graph of vertical distortion. If the structure breaks, then the crushed matchbox can be straightened and the deviations plotted. If many plots are made, then the graph may even be able to predict the failure point.
Start by gradually applying twice the load, as most general purpose machines should be capable of this with a little flexing. Standing with two people, then more if possible on the seat, then jumping up and down on the seat, lightly at first, then harder, reading deflection at each stage. Be ready to support yourself if the frame suddenly breaks.

If not happy jumping up and down to create shock loads, a water butt or two can be placed on the machine, mounted more securely using a sand bag and gradually filled as deflection is measured. As big buckets are not too stable, consider using a long plank or small ladder balanced on the seat, its other end on a suitably level item such as a chair of the same height, but free to move. This will keep the water butt reasonably level should the frame break.
Measure the water by pouring in one gallon at a time. If using a hose, measure the time for the first five gallons with the tap fully open, then check the timing and place the pipe under the water, so creaks can be heard. Alternatively if you don't want water everywhere, consider lots of bricks, or anything else you can get your hands on. When filling a water butt, a reasonable load can be applied. Water has a density of 1000 kg/m3. A cubic metre is quite large, but equates to the weight of more than ten average riders. One litre of water weights one kilo.

If wanting to find out how much load is being applied,
One cubic metre of water weighs one metric tonne. ( 0.98 real UK tons.)
One gallon of water weighs 10 lbs. 2240 lbs per ton. 1 ton = 224 gallons.
One litre of water weights one kilo.
(American gallons are almost twenty percent smaller than British gallons.)
Initial testing could take all day.

Anything larger than a matchbox on a strong support will allow the load to fall too far after total failure. If the machine crushes the matchbox after failure, the marks can still be straightened out and read off. Do not allow the frame to break and collapse more than necessary, as this can distort later analysis and repair. To reduce the distance of a failed structure, a graduated wooden wedge can be used to measure very small deflections in a small gap. This also allows simple measurement along the machine.
If suspension is used, then, when the suspension units bottom out, take the process slower after bottoming out, and always be aware of any creaks or other untoward noises. Use the graph to lot the potential failure zones.
Always wear eye protection.
When an unwanted noise is heard, but hard to find, use a prise bar under the frame to flex the set-up while listening with a sounding tube or kiddies stethoscope. Engineers stethoscopes are also quite cheap, about five quid from the large red shop which sells welders. They cone complete with sounding bars for inspection in all places on the frame. Using a simple home made cardboard sounding tube while flexing the loaded structure is also possible for finding potential weak areas. A spot of yellow paint on suspect areas will help build up a profile of how the frame performs.

A graph can be plotted of load against deflection. If many plots are made on the graph, then it may even be able to predict the failure point as the curve begins to deviate from the early profile.
At a very basic level, without tyres or suspension units, the deflection should be proportional to load, to give a straight line. This will gradually deflect more per unit load, so the graph is no longer a straight line as the maximum safe load is reached. Therefore draw the graph at the same time as it is measured, so any danger signs can be recognised.
Making three different measurements along the bottom of the structure will highlight localised deformation and possibly predict the point of highest flexing, which may or may not be the failure point, depending upon the design.

As the load gets towards the limits, with tyres and suspension, it is worthwhile checking the distortion once the suspension has reached its limits and can move no more, where it is the frame (and tyres) which must absorb further extreme loads.
At first, the suspension and tyres will compress, then the rubber blocks and finally the frame will begin to deform. Suspension curve will be gentle, followed by a steeper curve, then as the frame begins to distort, the load may increase for greater levels of deformation.
For simplicity, it may be better to remove the wheels and block the suspension units, so that just the frame curve is measured. If forks are removed, then the bending force on the steering head will also be lost. The frame distortion should be fairly straight for a while, then begin to curve. This may be just past the safe maximum load. Note the load as the curve starts, as this will help push future designs close to the limits without damage. Relax the load immediately unless testing for more subtle tests. If wishing to test to destruction, the curve will get worse, until failure occurs.

Failure may be a broken weld, a bent tube or one or more of many other failures. If not very happy with the max load, it may be better to rebuild much of the frame after early failure.

If the frame does not break, then seriously consider making the next machine a lighter design, with thinner metal and other design considerations. Wherever possible, try until the frame breaks, as this will highlight the weakest points. Breaking offers excellent feedback of the design, it's manufacturing, the welding abilities and a host of other clues which can only be read directly from the 'failure.'

It is unlikely that any bike will be pushed far beyond maximum shock compression, with the shocks on the hardest setting, plus half the rubber bump blocks. If the machine handles one and a half times this load without any untoward problems, then it is probably of sound design and manufacture and probably capable of much more load. If you feel confident with the graph, you may wish to push further.

If problems occur, return to repairing or making another machine in the light of experience. Many components can be salvaged, such as the steering head if they survive acceptably. Re-use only after checking for cracks, See later. The components which did not break should also be carefully studied. The remaining components will probably include the bearing housings, seat profile or rails and steering linkages which all take time and effort, to leave the next step with 'just' the frame to build.

To enable the suspension to be set up for minimal pitching during normal use, a ruler is used to measure the sink in front and rear parts of the frame under load. This assumes the working load will be the rider and mass of the machine, so the sink in the chassis is fairly level, or if you have more suspension movement at one end, then the sink under normal use is proportional to the amount of travel at each end. This allows the standard suspension units to be repositioned for a fairly level ride. If you have fork legs without an anti dive mechanism, then it may be important to add a little more mid range resilience and perhaps greater full range compression damping to the front suspension if you intend to do a lot of hard braking. With HCS, you should be able to fully or proportionally separate braking from suspension. Although at this stage this will be static testing and not include the dynamics of the partially sprung mass of the suspension, it will place the suspension in the ball park for general use.

The JP8 has a composite chassis which being radical, needed careful testing. The machine was first built as the core chassis and suspension, then tested fully for general load. Then carefully filmed to ensure the chassis flex was carefully controlled by using a digital camera in movie mode to see how it behaved dynamically. The subsequent set of movie clips help refine the composite structure to ensure the whole chassis and suspension systems were safely within the expected overload limits.

Fractures.
Look carefully for small fractures. By soaking the frame or component in thin fluid such as dyed alcohol, or ink, wiping dry, then spraying or covering in an absorbent film which will absorb the fluid and highlight the imperfections. Dusting with chalk, talcum powder or a thin, non glossy spray paint often works adequately. This is a cheap variation of the 'zyglo' method used for checking turbines etc. Discard if suspect, or carve back any damage and repair as necessary. Do not be tempted to simply fill a crack by welding unless perfect grooving and cleanliness is done to check the full extent of the fault.
Fractures may be caused by poor welding, excessive loads at the point or node, or by constant flexing at a poorly designed part of the structure. find out why the fracture evolved, then implement a suitable solution.

Do not get despondent in having spent so many hours building a machine to the highest skills, as this is never lost. Yes, heartbreak will often follow such preparation, but the next machine will be even better. A good apprenticeship is never easy. The builder invariably learns a great deal more by mistakes than making a perfect machine first time. The many who make a seemingly good machine first time should consider just how much better it could be with further knowledge and skills.

When things don't go as expected, try try try again.
From a poor chassis, to just an annoying gear change system, some designs may never work as intended.
In the unlikely situation that the second machine is also poor, then consider making a very adaptable frame and suspension first, until the handling is correct, then building a refined machine from this.
Salvaging whole sections from the old machine is often possible by reintegrating engine mount sections and such like, so that 'just' the frame may need to be rebuilt, even if using a different design. The test notes will help refine the next design.
If this also becomes a poor machine, then the geometry or construction or other areas may be at fault and testing must be adapted to highlight the problems and allow further modifications. consider adjustable rake and trail, adjustable seating and suspension, as deemed appropriate to the faulty aspect of the design.

If deciding to test on the road, always wear protective clothing until confident.
Always test first in quiet roads until confident and the machine is fettled as much as possible.
Suspect all possible frame problems until confident.

Never be too confident.

For the first few hundred or thousand miles, do not paint the frame, as you may need to make further modifications. Just use easily cracked, thin, bright coloured lacquer or similar on all suspect areas which can highlight problems before serious damage occurs. Lightly lacquered, tensioned tissue paper is also possible on suspect flexing areas.

Test rigs.
Long term testing need not be done on the road.
A basic test rig can be made from a barrel mounted on a axle, or just an old car hub and wheel. The rear wheel of the bike can then run on the test rig with the front wheel clamped. The rear held down with safety straps and a set load on the seat. If the outside of the barrel has a rough profile which is unsympathetic to the frame and suspension, then a basic long term testing machine is possible. Always have unevenly spaced lumps, so the deflections are over a wider frequency range. If drum width permits, make three various frequencies to be unsympathetic to the machines natural frequencies at different speeds and loads. If the car wheel tyre has lumps bolted into the carcass, then use an inner tube pumped up with water to give a firm surface.
The bike engine can power the system and help refine fuel consumption and cooling systems as a separate part of the same test.
If a barrel is partially filled with water and the spindle has paddles attached, then a load can be applied to also test the drive train on smaller machines. Water level can adjust the load applied.
If using an old car hub, the old car brake can be applied using a lever and weights on a drum brake using the parking brake lever. If hydraulic disc, this will run better with improved cooling and ideal for long term testing. Dripping water into a ventilated car brake helps cool the test rig.
If a car hub and wheel, the wheel could be offset with an unsympathetic spacer on the wheel nuts to give a wobble to continually move the suspension much more than simply fitting bumps to the outer surface.
If silenced adequately, the engine can be run for hours and a cooling fan or radiator header tank or domestic water tap employed to maintain adequate engine cooling. Use a car cooling fan or a fine spray over the fins of an air cooled engine. If noise is a problem, cover an air-cooled machine with cotton cloth in and around the fins, then constantly spray water over it while running, or allow the water to trickle over the cloth to maintain a cool heat transfer.

Always have a kill switch attached to the load, so when the machine breaks, the engine stops. Use a long fuel pipe, so the fuel is not detached, as fire may ensue from spilt fuel. Never allow the revs to run out of control, so a governor is required if unattended. Governors are not always available, usually having to resort to using the tick over screw to keep revs adequate when unattended. Preferably connect the suspension such that when it fails, the ignition shuts off completely.
It is not always possible to test a component for many hours under tough road conditions using the vehicles engine. Therefore some form of extended road simulation is required. This is particularly applicable to assess lightweight machines, suspension systems, composite live axles and such like.
To simulate rough road use, simply load the appropriate axle or both axles with a basic rolling road and load the machine with a dummy load. When the engine is not suitable, the simplest option is a barrel on bearings, such as a disused washing machine, where the drum motor is built up with irregular obstacles to simulate the conditions required. Washing machines have poor bearings, but will suffice until it fails. If the bumps are replaceable, then various simulations are possible. The typical washing drum motor is capable of a wide range of speeds and should be used to advantage. Washing machines are built down to a price, so don't push them too far, but if scrap, then ensure either the bike or washing machine will fail safely.
A simple test rig need not take up much room and can be mounted close to a brick wall, allowing the test rig to run for days or weeks.
Use bungees to keep the machine in position, but allow the machine to fail safely by ensuing the failure will happen in a safe manner should it fail when not under observation. This usually employs a slightly loose chain to support the failed machine and a simple kill switch above the load, so that when it drops, the motor WILL be switched off.

Test kit.
There are many ways to study the machine during the various testing schedules.
The advantage of using test sensors during normal use and during extreme testing, is that they give a ball park and a danger mark from which to assess the design.

Strain gauges can be built from a variety of sources and easily calibrated at home. They can even be integrated into the machine in areas of concern and calibrated during initial tests.
If new to this, begin with cheap bathroom scales which often use strain gauges. Re-engineer the components and mount accordingly, with the digital readout mounted appropriately. Cheap and surprisingly effective. Preferably use a passenger to read off while riding.

Deflection gauges need not be electrical and can be self recording, as mechanical deflection devices such as amplified arms can be welded to accentuate movement, to rub on a matt white painted surface to give feedback of the distortion in both directions. Similar to the basic, 'bendy bar' torque wrenches. Just make sure that the frame deflection is measured, not that of the measuring device. The machine can then be returned to the test rig and loaded to the marks, to assess the safety margins available. Use a piece of flat sheet to ensure the arm flexes only in the plane to be tested.

Digital thermometers can be adapted and also augmented with temperature sensitive memory strips where exhaust cooling airflow and radiation may be a problem.

If an old discarded laptop or hand held has analogue inputs and these are reasonably capable of differentiating between minor changes, possibly with the game control input, then an interface can be built to read resistance for strain gauges, pressure, temperature and other sensors. The BBC micro was an excellent machine in it's day for the purpose of static testing.
The PC game port is ideal for making simple test rig recordings.
Old 286/386/486 laptop PCs are usable despite their age and can become a dedicated part of a test rig. Even a simple routine can be run and stored on a floppy if the hard drive is dead and the bike can supply power !
If the screen is dead, use the VGA output and an old monitor, or write on another machine, then get the programme to boot straight from floppy and a single press of a key, and to stop when data size is enough for the floppy. A second key will transfer the data to floppy. With classic writing, a floppy can contain the OS, programme and still have enough room for data. For those who live dangerously, the floppy may be able to load the OS into memory or ramdrive, delete the floppy files, or most of them, read the data to be gathered and then write to the almost empty floppy. As this is a one way, do not worry, for a handful of similar floppies cost mere pennies.
Always mount a computer in foam rubber. Always mount away from moisture or in a poly bag when testing in the rain. Always record to disc for reliable storage.
Most PCs can accommodate a variety of input boards, with analysis software and virtual oscilloscopes. Discarded laptops with home made interfaces are ideal for road testing. Hand help digital 'oscilloscopes' are also useful, especially those with large memories. Cheap temperature sensors are available using a variety of car and other various devices. See aerodynamics monograph on this website for a simple floppy disc programme.

A simple spring loaded pendulum pivoting on a ceramic potentiometer can be calibrated for acceleration and deceleration of the bike or swing arms and other components. For zero and at plus and minus one G, calibrate against the effect of gravity. (Turn it horizontal.) A single rod with a mechanically amplified potentiometer movement placed across front and rear top shock mounts can give overall flexing under various conditions, applying this to the destructive testing schedule will help to highlight the safety factor of the design.
An absolutely fascinating array of digital devices are available for mere pennies. A classic example of ultimate cost effectiveness was the application of a 99pence digital YoYo to count deflections and a few other parameters. If new to this game and just needing a simple counter, use a pocket calculator and connect a wire to operate a switch connected between the + plus sign contacts, then input 1+1= and the switch will count on the calculator for ever. For rotating or non-contact parts, a magnet and a reed switch are ideal. This makes the simplest distance measurer if the circumference of the wheel is known, although cycle devices are more adaptable.

Once the machine is built, pocket lasers can later be clamped to the frame to asses the amount of deflection during structural tests. The little one quid keyring lasers can assess how frames ands wheels distort under load, and whether my asymmetric chassis suffer out of alignment forces under load, Then used to add materials, (or remove) to ensure the wheels stay as straight as possible under all situations.

Eventually you will have a machine on which you feel confident and comfortable and safe.

Real engineering is a craftsman doing for pennies what any commercial company usually does for a fortune.
Never be put off by the 'sophisticated' talk and equipment of 'experts'.
Decide the data to gather it and how to assess it. It's not black magic.

Well, by now you should have a decent and safe machine.

I cannot guarantee that a well built and accurately aligned machine will handle well, as many do not, although all of mine have been wonderful. But if you have made the machine accurately , then it is far more likely to handle well. If you have copied or followed conventional design, but modified to be tailored to you, then accurately built, then it should be even nicer then the best machines off the shop floor.

Copying others is no way to improve motorcycle design.
By making full size drawings from scratch, the design of the machine should evolve naturally with the above guidance and with feedback from testing. The lack of drawings in this monograph should hopefully have not confined, and preferably opened the opportunities for the overall shape and form.
Innovation should be the motivation and YOUR individual home made drawings are part of the path.

The very best machines have both good design and accuracy as their hidden, yet superb main characteristics - and this is what this web page has been all about.

I can honestly say that there is no better bike than a perfect machine you have designed and built yourself.

By now the reader should have generated many ideas with more yet to be created on the path into the future.
Welcome.

Feedback greatly appreciated.
Email jhpart@btinternet.com

(C) John Partridge. 1996 2002 2004 2006

Single sided rear ends.
Nearly all my bikes now have single sided rear ends, and often single sided front ends too. This is NOT because of cosmetics, but as part of research into an area which seems to have faded in the late 2006 /early 2006 season. There is far to go with single sided rear ends and manufacturers may have lost quite a few good design tricks by going back to traditional rear suspension systems.

The torsional effects of supporting a wheel from one side will often lead to compromise of the frame. The ability to support a wheel in an offset mounting is an interesting engineering challenge, but can lead to serious road accidents. Similar applies to front ends, where failure of a single sided front axle will usually lead to an even more dangerous situation. Single sided front and rear ends have their attributes, but weighing the pros and cons can be difficult when building an ultra light machine or an advanced technology demonstrator or road legal test rig.

Live axles.
Because of the nature of single sided rear ends, a live axle is almost always used. But it is not the only possibility.

When building live axles, always over-engineer until the design has proven itself. Then gradual lightening can begin, although if any removal of excess weight is to be contemplated, then live axles should be considered last. Metal axles should be polished or peened to prevent fractures.
If testing an axle design to the absolute limits, then integrating a secondary safety axle inside the main axle will offer a degree of fail safety. Never let the safety axle assist the main axle, so the main axle can be allowed to fail under normal conditions.

For a touring or commuting machine, heavier bearings may be needed on machine with the inevitable amount of non standard overhang of bearings which may occur. Never have any more axle bearing overhang than is necessary. Most overhang will depend upon the type of brake used, with discs usually offering the least overhang. Ideally the bearings should be equally spaced either side of the centre line of the machine. If different sized taper rollers are used for lightness, the larger can be the load carrier and positioned on the centre line of the machine and the small one merely to supply secondary support and alignment, usually beside the sprocket.

A wheel supported at one end by a live axle will flex it's shaft through a full cycle of distortion every revolution. This is a massive number of deflection cycles over many years. The axle will probably work perfectly well for a short while. Long term failure is the main problem. Always strip regularly for inspections and always assume the worst, and design the shaft to fail as safely as possible. Minimum overhang reduces the problems.

When making a first working design as an engineering challenge, most axle designs may work well from the start. Always beware of false confidence. The main problems occur from long term failure. Building a basic test rig and testing the axle for many simulated years will be ideal, but such luxuries are rare. As mentioned earlier, this is possible with a little thought and a big test roller. If the engine is not to be run, perhaps testing just the rear axle sub-assembly, then consider an old washing machine and its motor. The clockwork timers also can sometimes be 'modified'.

If testing the chassis, use old chain and sprockets, which usually accentuate the problems. For testing a specific part of an axle or wheel at high speeds, it may be preferable to use new chain and sprockets which will allow early, slight problems to be recognised more easily. For general use, use old, worn chain and sprockets, especially if replacing the engine with an electric motor to drive the assembly until failure or reliability is proven.

Bearing sizes and mounting.
The following will assume the use of a steel, possibly tubular, live axle. The ideal bearings are taper roller, but the finite adjustment they demand is unsuitable without a lot of engineering of threads or shims and associated weight disadvantages. Accurate pre-loading of angular contact bearings such as taper rollers can be fraught with problems for custom builders. Where finer threads are not possible, a superb work around is preload, where a light Belville washer is used to preload the taper rollers, offering perfect maintenance free adjustment over many decades. Belville washers when carefully machined without overheating, will retain their spring properties and can thus be modified to match the particular needs of the design. Shims also possible.

In the real world, ball bearings or a ball bearing for alignment with a needle roller for load is quite good. The ball race is employed to maintain position on the axle, with the needle or larger roller to take the centre line load of the machine and rider. If mixing taper and ball, then the ball race must be deep groove type, to permit the axial end load required by a taper roller.
For minimal friction, the ball race is king. For long term reliability, the roller is king.

Because live axles are by their very nature usually larger in diameter, physically larger bearings are needed. This can lead to excessively large hubs, unless good bearing choices are made. There is nothing wrong with large hubs, but weight of materials to support them should always be considered. There are lighter, safer ways around this and are under study, but still being developed at time of writing.
Variations on many bearing themes are available. Check with bearing suppliers and ensure needle rollers come with inner races as they have to take most of the weight of the machine and rider. Needle rollers are available with axial load ball races on their end faces, which can also take care of side loads. A bearing guide available from any retailer will help decide the loads and other info. Ask about variations on INA's NX series of needle rollers or their equivalents if needing a particularly compact mounting with side load capabilities. Another good guide is straightforward comparison with standard motorcycle bearings as used in similar designs.

As it is difficult to build and fit an axle with two fixed flanges, it must be decided whether the sprocket / cush drive, or if the wheel is to be mounted on the permanent axle flange. The cush drive is often taken direct from a donor machine, and keeping the metal sprocket and mounting will liberate the rest of the rear wheel design to be in lighter materials.
Cush drive variations on rubber bushes as used in the rear wheel of the Honda XL185 series makes for a simple cush drive. When bolts are used instead of pins, the sprocket will still need to be axially aligned and constrained. This should be an oversized boss or flange on the sprocket carrier, which is dressed to fit the standard sprocket by machining in place for prefect concentricity. Always grease metal to metal cush drive components for reliability. Where a sprocket has large lightening holes, these can often take cush rubbers. Similar, if not identical to 916 style.

When mounting a sprocket onto the shaft, the alignment of the appropriate cush drive should give strong shear planes at their mountings. The wheel and sprocket sides are probably connected on splines.
If expensive engineering is not available, such splines can be employed by modifying a car front wheel drive axle unit or motorcycle or car gearbox splines and their components. It takes time and effort to hunt down suitable components, but saves an awful lot of engineering work.
One side of the live axle can have a permanently mounted drive flange. The other side must also be fitted perfectly concentrically, but must be removable. This often causes problems for those without engineering access. The classic taper fit and parallel or woodruff key are acceptable, but a precision spline is better. Splines can be taken from other devices. For small motorcycles, consider splines such as gearbox components. For larger machines, car drive splines can be re engineered to integrate into a live axle. The standard front drive car axle is heavy, but easily lightened for motorcycle use.

If no cush drive is employed on the sprocket side of the axle, then the wheel can be bushed, or have a central bearing and slide over the axle. This will allow the wheel to rotate on the axle, so that flanges can fit into rubber blocks to act as a cush drive. Shaft drives usually have their own built in cush drive units, often a spring and ramp design.

The normal single sided rear axle mounting, often uses a large eccentric housing with chain adjustment which is clamped by the swing arm. Similar to Triumph, ELF(Honda), Ducati etc. This is acceptable in metal, but split housings offer particular problems which may need to be overcome with careful design. There are at least a few other ways to do this, such as a single outer tube for maximum strength and have the inner eccentric expand outwards to lock the axle housing in the position of adjustment.

There are more radical alternatives, with the JP8b,c having guaranteed perfect wheel alignment, lighter, minimalist rear axle with smaller bearings and constant, perfect chain adjustment. The later JP9 series rear axles will be even more advanced and fail safe but presently under development at time of writing. The latest design is absolutely superb and uses lateral thinking, but will need patenting. See later monographs.

On some designs, a front engine sprocket can employ a sprocket shaft mounted disc brake, when the ultimate light rear axle wheel assembly becomes technically closer. But only if the lower chain run is under control. If the final drive gearing is 3:1, then a disc one third the power is needed, but thrice the wear.

Single sided axle mounting in the frame.
Once the rear axle unit is built, it can be used in conjunction with the wheel to align itself into the frame. (Also for front axle for hub centre designs.) This usually employs the Vee blocks for horizontal alignment and an accurate measure or stud bar adjuster and set squares for a parallel alignment in plan and end views. See above.

The main problem with single sided hub bearing housings is in their support. Supporting the axle housing in a single sided swing arm may require many methods to be employed in concert to successfully maintain acceptable rigidity for control of wheel alignment. The major possible design considerations are internal or external bracing to control torsion from any excessive overhangs. Others include box sections, space frame or even other structures for ultra light machines as used in various aircraft and other designs. The ELF series of 24hr racers illustrate some of the design possibilities and problems.
The simplest is to model at full scale. Reading the way the design finally fails will highlight the probable way the forces are acting and where. Scale models do not always model truthfully at full size, but full scale rarely goes wrong, although the loads are much higher but certainly accurate when testing.
When a full scale test rear end or swing arm is proven, then it can often be directly used on the machine, so always build the swing arm and rear axle in such a way as to be able to test it fully, torsion and vertically and lateral forces, and thereby save building another if it works well. Done properly a rear end should integrate easily or with minor modifications to the final design.

Modifying an alloy rim is only applicable if wanting to keep the original wheel pattern, but wanting a single sided car wheel centre but with a narrower rim profile. The simplest way is to set the outer rim as the designed reference with offset from the centreline, using a standard bike rim as a centreline and profile gauge. Then carefully run the rim on a driven wheel, and make up a wooden framework to act as a lathe. Welding a couple of brackets to the swing arm makes for a reasonably good lathe, powered by the bike engine or a sprocket on a washing machine motor or a long suffering electric drill.
Securely mount a cutting tool such as a broken off hacksaw blade into a block of wood or on the swing arm, and use this on a lever system to gradually cut away the other rim. If done carefully, then the rim may be removed in such as way as not to damage the main wheel structure. Done neatly, the removed rim can be moved closer to the inner rim and then be welded. If very neat, it can be bonded using aircraft adhesive and a few 'chicken screws'. Use the original bike rim profile as a mounting gauge for excellent accuracy to the unchanged rim.

Once a decent form of rigid swing arm is designed, it must be able to blend into the main frame. Do not build a superb swing arm which mounts poorly onto a frame. Some otherwise superb machines are let down by poor swing arm mountings. Developments in swing arm mounting and design has far to go and may follow in later monographs.

Wheel mounting.
Mounting a wheel using a live axle can be done in many ways, but usually requires large diameter bearings on a live axle. See above.
The ability to slide the shaft into the swing arm from the wheel side, will allow the wheel to mount against a fixed drive flange. Upon this flange can mount the disc brake. It is always preferable to be able to easily remove the wheel to gain access to the brakes. See brakes.

Once the axle with sprocket is fitted on it's bearings, it can be mounted in the frame and turned to dress the wheel mounting faces accurately. Mounting the shaft in the bearing tube in the frame will allow the assembly to act as a lathe via the engine if needed.
For general use, a lack of a proper lathe is not a problem, as the axle becomes its own lathe once the chain and sprocket are connected to the engine. Unfortunately, this is a chicken or egg dilemma when careful alignment must be approached in stages, and tack welds used until an accurately mounted rear wheel is finally ready for alignment in the frame.

An alternative with live axles is to use an electric drill to drive the axle as it's own lathe, but the drive is too light for a lathe tool, so a grinder should be used to accurately remove metal. A rubber compression mounting in the centre hole of such axles can drive them. Use a rubber tube, two washers and nuts to compress the rubber into the axle and a long piece of studbar, then bungee the electric drill in a temporary mounting, or have someone hold the drill. Even small cuts are difficult, so use a swing arm mounted grinder to profile the components. Any similar method is always useful prior to mounting the wheel and rim.
A simple cutter bracket can be mounted upon temporary swing arm mountings. If the cutter mount is weak, chattering may occur or other lathe problems. Run the axle at various speeds with small cuts until a suitable cutting speed can be decided to reduce inaccuracies. Try to run the engine at its smoothest speed and use the gearbox to control the cutting speed. Preferably run the chain tighter to prevent chattering of the power train. Always wear gloves and eye protection when machining. When using 'alternative' lathes, never use speeds higher than needed.
There are many other ways, but the point to be noted is that not having a lathe is not a problem, just a minor challenge.

Hub centre steering.
A whole monograph in its own right could be written here and a monograph will be published once the JP programme has finished, should funding permit. Meanwhile, a few pointers.
Don't think that the best bikes available today are all that is possible, the future has a lot more to offer and it does not need lots of money and a parts catalogue. It needs imagination, skills and will.

Hub centre has many attributes which often, but not always outweigh the disadvantages. Hub centre steering has few and occasionally no disadvantages, but depends upon use.

One major advantage of hub centre steering is the ability to separate steering from braking and from the suspension, physically and geometrically. Therefore the braking does not upset the steering or the suspension, and the steering does not upset the braking etc. When you put on the brakes, the steering does not change and the suspension does not dive or misbehave. Therefore you can set up the suspension just as you want, and adjust the steering and braking to perfection without worrying about all the malarkey associated with forks or other compromised systems.

For development machines, the ability to adjust rake and trail is an absolute treasure. Being able to do so while riding is even nicer when setting up and fettling a new machine.
For researching unusual machines, this opens the eyes much further than expected. Riding hands off at high speeds down a long, steep hill with almost zero rake and trail with a low centre of gravity is a real eye opener to absolutely superb, positive, yet sensitive steering. The author has ridden a vast range of motorcycles, from trials up greasy rivers, to Ducatis around Silvertone, but none has been as responsive as the JP5a/b and JP6b series across the fast and twisty roads of Dartmoor and Snowdonia.

For developed road machines, the ability to have true antidive, lower centre of gravity, zero stiction, total independence between suspension and braking, lower design height and greater adjustably of the design, invariably makes for a better all round package. Therefore make every effort to design and develop a machine which can do all you want, and more.

If wanting hub centre design, then work out as before, the overall wheelbase for best axle loading, then work back. Decide the best angle for the suspension movement, then find the best swing arm pivot point , if you decide to use swing arms.
Next work out the steering lock needed, and build the most suitable swing arm or other suspension set up.
Make a hub centre unit based on a suitable dished or spoked wheel according to the chosen design path.
Decide the best place for the suspension units.
Make the steering linkage to act harmoniously and safely with the best ergonomics.

Single sided rear ends have minimal offset of the swing arm, just enough to clear the various tyre sections and diameters. Single sided front ends need a vastly larger offset of the swing arm to enable a reasonable steering lock. On long bikes this needs even more steering lock to be comparable with conventional forks. Excessive offset of the front swing arm can cause a great deal of flexing, but suitable design using box sections, space frame or other designs will give a theoretically better chance of making a better swing arm structure. It is not as difficult as might be expected.

The common asymmetric design will naturally lead to front end distortion unless designed well. Overall chassis counterbalance of the asymmetric mass must also be considered when designing the frame, engine and rider ergonomics. Even when dual sided hub centre designs are used, such as the superb Difazio series, there often remains problems with poor steering lock and wheel and steering bearing choices.
There is always a middle way for those who need a design escape path from traditional forks, such as offered by certain German boxer twins and Hossack plus many others.
Note that the Hossack shown here has the front frame suspension pivots beside the cylinder head, with the handlebars on extended frame tubing and the front shock is beside the carburettor. This could work well with coupled single sided rear suspension.
See also the Ner-A-Car, 1920's onwards.

If making wheels, then the heavy dished wheels needed for single sided designs can work very well, but central steering bearing housing will remain an area where alternate steering parts from other vehicles may be preferred.
Because of the many design subtleties involved, a first attempt at hub centre steering may not be as light or as rigid as a standard machine. Do not despair, quality comes with practice and continual refinement.
No two hubcentre designs seem to look alike, even from an engineering or geometric viewpoint. Tony Foales website gives the theory, which the reader should study, then design their own back through engineering and experience.
Whatever design is created, always overbuild first to test if it works as required. Then gradually underbuild to test to destruction with the intention of understanding where the weak areas are, then build and prepare to enjoy the first of such refined variations.

Before designing the braking linkage, it is important to decide how much anti-dive is to be incorporated. Very few designers use complete antidive, as a little dive while braking enhances the feedback process to the rider. Reading of Tony Foales excellent work on this subject is well recommended for the geometry involved and is available across the internet.

Here is a formula one development steering wheel, as opposed to the race wheel, and as can be seen, they are easily adjustable electrical control dials. These are surprisingly similar to superbly ergonomic 1950's radio dials, but that's where the similarity ends.

Start by building little test rigs at home by soldering various components together. Then test rig them under load, perhaps using old car seat mechanisms to control the various suspension or ergonomics of the bike. Always overload the design to give a good safety margin.
When finished, tidy the design and encapsulate in resin then integrate with style. Any heat items such as power transistors or thyristors must be mounted on alloy fins, preferably in a cool airflow.
I modify car seat motors to give my motorcycles adaptable steering angles, and adjustable suspension rates, using chassis mounted sensors to give the bike tighter handling when the cornering gets fun, and gives modified braking according to the road surface, moisture and such like.

Electronics gets far more complex when making your own paddle gear changes and servo shifters will need adjustable damping of the clutch, but the matching of the engine revs for fast gear changes is always prone to problems.
It is very easy to shift up when the engine reaches its red line, but for normal use, a smooth and faultless gearchange in automatic mode is very prone to problems. As gear changes don't always happen when you want them, it is always better to have a paddle control and add semi automatic for lazy touring as an option, only fit for main roads and motorways.

Integrating the engine and the suspension can really mess your head up and adjustable controls WILL be needed.
Always build in analogue systems first, to see if the concept will actually work and only then should you consider writing the programme for eprom in a simple control chip such as the PIC series of micro controllers. I started writing machine code in the eighties, and this game its always plagued with problems.

A few experiments with electronics can soon escalate the costs, so keep costs in context and scavenge from discarded electronics and other scrap sources.
Old videos are an excellent source of small bearings, shafts, motors, pulleys and switches, even battery chargers. For larger parts, I use car components, especially a badly damaged car seat, with ripped leather for a tenner will give excellent servo systems, of you fit your own potentiometers, otherwise just use the motors and systems in a primitive form, but just add end stop micro switches.

Anti-dive front suspension is still the forks main problem, so it is probable that electronics will soon be integrated into the damping control mechanism. Simple electric actuators to adjust damping according to brake pressure and road conditions will probably soon be included, so consider integrating such ideas from the outset. Anti-dive front suspension is still the forks main problem, so it is probable that electronics will soon be integrated into the damping control mechanism. Simple electric actuators to adjust damping according to brake pressure and road conditions will probably soon be included, so consider integrating such ideas from the outset.

Adaptation of quick shifters to electronics are comparatively easy, but fail safe measures should be employed. These may be integrated to read the tachometer and throttle sensors and preferably adjustable for economy, sport settings, or to be speed sensitive. Logic and other ideas may not be applicable for a few years yet, although the multi-D map will enhance the operation until pseudo intelligent software is successful.
Gearchanges may be set up to shift only at read line if needed when at full throttle, with more sensible variations created according to personal taste. Changing down can be adjusted so that twisty roads change down to keep revs higher for better engine braking, whereas on steady straight roads the gears can be changed to keep revs low for touring, redlined for racing
Do not expect any electronic system to be able to read the road ahead, not its condition, even if you have faith in satellite systems. It is always best to choose the profile for the road by using your eyes and the seat of your butt.

Wherever possible, always integrate as many variables as possible with easily adjustable rotary potentiometers and all that's needed for adjustment, preferably in real time while riding. Digital systems are not always better for development, as writing in machine code or assembler can occasionally cause unexpected problems which cannot be easily overcome. Analogue systems can then be modelled and shaken down in digital form once the concept works as required.

If worried about fail safe, three identical control systems can be wired to the same inputs, then wired to simple logic so that if one fails, the other two will override the faulty command. Simpler, but similar to the space shuttle system. Further logic can be used to notify the problem via a warning LED or other device. Wherever possible, use independent sensors, as where it is possible to fit one wheel sensor, it should be just as easy to fit three. When testing, always make the three designs slightly different as calculations are not always infallible.

Car and other engines.

Air cooling is simple on engines such as the 2CV, '4CV' and they are often used for low centre of gravity, but the wider mass often negates the rotational mass effects. If weight is a problem the crankshafts and flywheels can be lightened as bikes need less flywheel effect, and alloy barrels are available for some machines such as the VW beetle engine for aircraft use. The art of lightening and balancing an engine is available in many publications.
When mounting these engines into motorcycles, either consider an automatic version, or fit an intermediate adapter plate to take a German or Russian boxer gearbox or similar. If keeping the original components, lock or weld the differential, so it does not explode.
Some 2CV's have an centrifugal 'automatic' clutch, where the clutch releases at low revs.

Many car engines are possible on two wheels, and although V8's have found their way into motorcycles, the designer should seriously consider the prime purpose of a concept.
A variation of the JP7 has been designed for a 2 litre engine, auto transmission with two wheel drive and although technically capable of being built today and comparatively simple, it is not going to add any true advantage over a modern motorcycle engine as the main limitation is public acceptance.
Motorcycle engines have a shape and output more suited to a lighter chassis, whereas a car engine is often too bulky. There are also many other variables such as inadequate tyre technology. The likes of the proposed Rocket Three and subsequent heavier duty motorcycle tyres, then such bikes with larger engines are more likely.
If aiming for unusual engines, consider aero engines which tend to have lower revs and fuel economy, or at the other end, snowmobiles will often offer a much better hunting ground. See also Monotrak Engineering.

When making gear changes on standard car gearboxes, the subsequent four or five way linkage is best modified by extending the shaft sliders and connecting the internals directly to a rotary plate or a rotating shaft with grooves, in the similar manner to a motorcycle gearbox. As gearboxes are not pressurised, minimal oil retention problems should ensue from the simple splash lubrication available.
When using car gearboxes, never try to lock one side of a diff to double the output speed of the other shaft, as the diff will simply explode, as the internals are not designed for this kind of speed or load.
Many people prefer to fit BMW or Guzzi gearboxes and rear ends to car engines for obvious reasons. Modifying the intermediate shaft and a thick sheet of alloy between each will allow a simple mounting interface to be drilled to accept the various bolting patterns.
Making a flange plate to take the engine and the gearbox mounting bolts can be easily made form a large sheet, while ensuring the spline in the centre of the clutch plate is all that is in need of careful alignment. Even the bike types of dry clutch plate will fit into a car flywheel.

Using car style gearchanges may require fitting a foot clutch, or a clutch lever on the gear stick, as they cannot be operated with the clutch on the handlebars. If formula one style sequential gearboxes are available, seriously consider choosing them wherever possible.
If a hand operated clutch is to be used on a car engine, seriously consider making a hydraulic version. If still too heavy, then consider adapting a small car vacuum servo brake system. Cable clutches are possible. As the bike is much lighter than the car, the clutch is less likely to slip under the lighter load, so a few of the clutch diaphragm spring fingers can be removed for an easier life. Always remove fingers symmetrically for good rotational and pressure balance.

Adapting clutch or throttle cables to car engines is fairly straight forward, although the cables will be often need to be modified. As it is increasingly difficult to find anyone who will make a custom cable. Improvise or make your own.
Improvise: Using standard bike throttle, position the cable in the best route towards the carb. Then use the standard car throttle cable and route this towards the front cable, they will either reach or not reach. Then make up an intermediate connection to fit these standard cable ends, Then make suitable outer cable clamps to position each outer cable in a suitable position along the frame. By keeping to standard parts, many hassles will be negated.
Make your own: Find a supplier and buy plenty of inner and outer cable. If you have friends, your cable skills will soon be in demand. For throttles, choose the more flexible inner cable, as the throttle should be a light action. Outer cable should be nylon lined. Also buy a good selection of nipples and ferrules at the same time.
Scavenge the ends off the standard cables to make a good fit for the twistgrip, and clean up to fit the outer cable. Where the outer will not fit the standard mountings, slide a short length of rubber fuel pipe over the join to prevent misalignment of the cable run.
When cut to length, fit the outer and check the run. If you cannot find suitable nipples, then make your own from steel or brass. Brass is better as it solders easier and wears better. Old brass screws can supply the twist grip nipple, by drilling a small hole first, then countersinking the hole slightly and then cutting to length evenly either side of the hole. Larger nipples may need to be made from old steel bolts.
The inner cable should be soldered around the new ends before cutting, so the strands will not distort. When the strands are in the nipple, file a small nail to a tapered point and gently hammer into the centre of the strands to swage the strands open and spread in the countersink. Then solder fully and file flush when solid. Make sure the nipple will rotate freely to prevent undue wear in the twistgrip.
The carburettor end may require a similar fitting, or possibly use a push bike brake type of clamp to secure to the carburettor linkage.
Always lubricate the cable fully before final fitting and route it carefully. If the car carburettor return spring is too heavy, try modifying, or use a different spring. Double check it will not stick open and always use an ignition kill switch if in doubt.

Choke. Where needed the choke lever can be mounted almost anywhere, possibly even with a simple high tech variant of a piece of string and a return spring. (Please don't.)
Some vehicles can use aftermarket manual choke conversions for those who prefer this option.

Making your own engine.

But in the real world of proper engine modifications, then a great deal of decent and genuinely applicable adaptations or modifications or replacements are possible.

With a vast array of cylinder heads, barrels, cam drives, gearboxes, primary drives and such like, all the parts are available, with just the need to build custom crankcases. If you can assemble the internals in a particular manner to work together, then it only needs a good crankcase to hold them all together.

Choosing a crank with the desired stroke, and if multi cylinder, then also with the appropriate crankshaft angular displacements, (boxers and V twins use a single throw crank pin, so both are suitable for cross breeding with some appropriate crankshaft balance changes.)

Sometimes a machine will be so radical that none of the many variations of motorcycle engines will simply not do. Sometimes adapting the design to work with a standard or lightly modified commercially available engine is preferable if selling many machines.

Occasionally the replacement of the barrels, cams, carbs or gearbox may not be enough, as sometimes the ideal engine is simply not available.
It is unlikely that a sole mechanic will be building their own engine, but with the greater access to alloy casting techniques and also the projected use of composites into crankcase design should be considered. This follows work done by formula one gearbox design, the possibilities increase and can only get more exciting. Eventually aramid armoured, flex free burst proof gearboxes and engines may be possible. This is under study by the author, but has far to go.

There is every reason why a one-off engine can be built. There is no need to reinvent the main components, as one can buy very high specification pistons, wet liners, cranks, whole gearboxes and such like 'off the shelf' or from donor machines.
Then with careful use of mixing the components, a special machine of ones own design can be built without undue difficulty, although cylinder heads, cranks, gearboxes and such like should be chosen from the selection of ready built components. The only reason this is not often done is because it is so easy to buy a motorcycle engine in almost any configuration. When a safe design in composite is required, the Rover long bolt engine is a very fine design for inspiration, using the approach of using the main components held in compression.
This long bolt design also lends itself to very easy, billet machined engine cases. - the crankshaft bearing are line bored in the billets, then the rest milled or ground out to take the crankshaft, then the barrel holes naturally aligned over the assembled crank, rods and pistons, then clamped in place with a standard cylinder head to match the crank layout. The barrels and pistons may be from any machine, with the cylinder head lightly modified to match the donor piston porting and can timing. The barrels may be wet liners, surrounded in a simple, non structural composite water jacket. the main billet holding the crank can then be bored to take the gearbox and primary drive or adapted to drive come other system, perhaps a small automatic car drive system or realigned gearbox.

The nearest engine design may not be quite right and although the choices are almost limitless, modifying or making your own engine can involve massive amounts of design, lateral thinking and trial and error. The JP7x has been designed with a two litre engine, two wheel drive with a highly advanced drive train which merely awaits funding and decent tyre technology. An early 2x2 test rig using a smaller engine worked well.

For other builders, an intermediate solution may be an engine from other sources. A classic example is the Yamaha R1 engine as used in snowmobiles. Snowmobile riders know a large amount about exotic engines and often put motorcycles to shame. In this case, the Yamaha 1000cc motorcycle engine is linked to an auto trans for stunning acceleration.
For low revs, light weight, high torque engines, also consider small and home built aircraft. For efficiency, propeller aircraft engines limit the revs to keep the propeller tips below the speed of sound.

For example, perhaps you have exhausted all the engine possibilities and want the engine section laid flat, with the cylinders horizontal rather than vertical, possibly horizontally to the front or to the side. In such cases, you must understand that you are not upsetting any basic forces, simply changing the cylinder orientation and the relative vectors. The engine will try to resolve the same forces involved. This is translated in the changes of direction and speed of the piston mass into the crankshaft and into the crankcase and then the frame, all of which may vibrate differently relative to the frame. By changing the orientation of the cylinders, these forces will change by the same orientation, so different mountings or extra reinforcing may be needed to absorb these forces. For example, a vertical big single may give large horizontal fore and aft displacements, such as seen by the flexing forks when ticking over. Then when modified to a vertical cylinder, will cause the vibration forces to be vertical. In some cases, the engine may possibly require different crank balance factors. This may only need removal or additional welding to the crank to vary mass. To check the vibration differences, simply dry build the engine and run the engine via an electric motor to check the major vibrations and enable easier modifications for checking. A vee pulley on the crank where the alternator would fit, and an old electric motor plus plenty of oil squirted into the shell bearings may suffice.
If the cylinder base is to be blanked off and a new plate of alloy is to be welded to take the repositioned barrels, then the cylinder studs seat into areas which will spread the load evenly across the whole crankcase, so some redesign may be needed to ensure the new locations are strong enough.
Where the engine is to be separate from the gearbox, perhaps separating a crank case and re-orienting just the engine section forward, then the drive should be carefully assessed. An intermediate drive may be used if this is separate from the rest of the engine lubrication system. Modern primary drives such as toothed belts have become quite sophisticated, efficient and reliable.
The builder must supply the oil to the bearings correctly. Sump design and upper camshaft lubrication may also need modifications.
Various layouts may be optimised for weight balance, or ergonomics for low centre of gravity, or a host of reasons. At a simple level, a water cooled touring V twin has been turned sideways to make a flat tracker engine. When separating the engine, perhaps using two crank cases, one chopped down for the gearbox, the other for a basic engine, ensure the oil system works as originally intended, although it may be possible to use the oil pump in each unit separately, or to connect them together with extended oil lines but with minimal restriction to flow in the plumbing. In dry sump engines, the frame can become the oil tank, allowing a vast number of possibilities for the engine, transmission and sub systems.
When Mr Cooper decided to use the engine as part of the chassis, he was but one step from fully integrating the engine as part of the frame.
There are many advantages to keeping the gearbox and clutch, or cylinders and head as original units. Modified or additional oil drains may often need to be added if the orientation is changed, especially if parts of the design such as the cam-chain tunnel which is used for oil drain is not low enough at the lowest oil drain point. Always make sure there will not be hydraulic lock of any mechanism from pooled oil areas, especially of bucket cam followers. You may possibly need to add large bore plumbing to the lowest parts of the cam areas, or modifications to the camchain tunnel to allow the oil to run to the sump by gravity.

Modifying engines can take many courses, the simplest is to modify the original set-up, possibly welding a new alloy billet slab to the crankcase and machining it to take the realigned barrels or other components. Some may wish to keep just the engine, and add it to a different transmission, possibly by turning it through various degrees. In such cases the removal of the gearbox and clutch may be machined off the crankcase, blanked off and the power take off of the crankcase modified. Whatever is done, be it in radical or moderate modifications, it is always better to keep whole assemblies intact, especially those with high forces, such as keeping the main bearing areas of the crankcase integral with the barrels and head. A classic example is the modular approach of the early MV Agusta racing fours, where the whole engine sub assembly, complete with crankshaft, could be removed from the crankcase and gearbox. A fine object lesson at looking at engines in a fundamental way. The 1970/80's Jawa six day enduros are also well worth a second look, as their crankshaft can be removed without taking the engine out of the frame.
See also Rokon and Monotrak. These may be old designs, but can still teach a lot about alternative engineering design.

If making a new form of engine from scratch, the probable course is new crankcases which can take standard barrels and engine components.
The superb pressure injection alloy castings of the Japanese are a work of art. This is not so easy to match, but crankcases to a high standard are possible using the skills and services of the few remaining alloy casting firms in the world. It may be hard to find a foundry which will cast one-off items, but they do exist. Finding them is the primary requirement. Some older, traditional British schools may retain some of the equipment, but are disappearing fast, as skills are now replaced by ability to pass exams. In a few cases, it may be preferable to consider your own casting, although the furnace will be the major cost, after which all else is essentially free. Making your own from scratch is a little too far too involved for this monograph at present.
Once the foundry has been found and negotiated with, the reader must decide what is needed. Alloy castings start with a set of full scale drawings of the basic design. These are then refined to take into account all the forces and other requirements involved in each design.

Assuming a water-cooled V twin components are to be used in a different configuration, perhaps horizontally opposed, perhaps turned through 90 degrees in the frame. Perhaps a water-cooled in-line 900cc triple with wet liners is to have horizontally aligned barrels or modified to fit a German in-line transmission. The choices are vast, but basic engineering of engine balance and power train must be considered fully.
(In most cases, adapting crankcases to fit shaft drive components is often better done by building up the crankcases with weld and or extra billet metal, then re-machining.)

First the design of crankcases must be drawn full scale. Then refined to allow the various engineering forces and fittings of standard components. Then the oil galleries and oil flow areas decided. This includes internal plumbing, draining and probably cylinder head modifications for draining.
The coolant must also be considered fully. If standard barrels are used, the new orientation may be problematic, at least for bleeding air from coolant and oil lines or hot spots and potential distortion of the barrels.

Although not an ideal example, desmo heads can illustrate the various thought processes required when evolving a design. Both are narrow angle valve, as in the latest tradition, followed by most engineers for an efficient squish and high compression and higher start flows of air mass. The older engine with ball raced camshafts, while the latest has camshafts riding direct in the cylinder head. The traditional Italian philosophy of building a machine which can last for ever, using ball bearings ensuring a longer life is wonderful for those who still own such older machines. But this route is not always so appropriate for winning races. Bearings are heavier, the rotating mass is higher of the inner races and then add half the mass of the balls and the extra distance from the axis. The overall volume of the cylinder head required to hold them is larger, therefore heavier and access is thereby restricted in this design, although split head can be used with ball races. On the right, the latest cylinder head which also has a lower cost of manufacture and assembly. The main advantage is less rotating mass for racing. There is increased shear on the plain bearings compared to rollers, but as the engine is constantly being accelerated, the differences between greater mass of a ball race and oil shear of plain bearings are more open to controversy.
Without the energy overheads of the valve springs, the natural ability of the desmo head to greatly reduce the load on the cam followers and cam makes the design ideal for the lighter loads and this lighter plain bearings in the cylinder head. This is a natural development for many excellent reasons.
A major advantage is much easier manufacturing and maintenance access. The machining of the new head is vastly improved, allowing mass production techniques to be applied directly. The restricted cavities of the earlier head required superb castings, but when this is applied to the latest head, the effects are simply superb. The easiest, safe machining of a component is always a very important part of design.
The subtleties can be seen with the position of desmo cam followers which is not necessarily on just one side, as the line of the valve is the engineering constraint. In the old head, tradition was followed as from earlier machines. With the new head open to greater access, the possibilities were larger. The lower followers for closing the valves are now pivoted closer together, using a different, right angled cam follower, allowing an even narrower valve angle. The opening cam followers are now positioned outside of the valve, making access, maintenance and assembly easier.
Although unlikely with modern manufacture, the bearing surfaces on the cams bears a closer note. On Japanese engines, heavy valve springs are used and poor maintenance can damage the cylinder head in the cam area. On a Desmo, the closing forces on the cam are upwards, into the theoretically replaceable upper bearing supports. Closing forces on the cam are outwards. This places the varying loads on the cam in two distinct places, and this reduces possible wear by half. With the desmo not needing valve springs, these forces are even less and only comparable with valve springs when the engine is at max revs. At all revs, this would be a very comfortable camshaft and at low revs, the forces are incredibly easier. The bearing wear areas on this cylinder head is unusual, well designed and typical of the forces to be considered when designing engine components. It is easy to see why engineers are highly respected in Italy.
In a vee twin configuration, both cylinder heads are water-cooled, both must be capable of good coolant flow in upright and horizontal if just one set of castings is to be used. In modern design, these are now different, but if designing your own, it is common to ensure one set of patterns will allow machining for both design requirements, with machinable bosses for most conditions of coolant flow and also lubricant draining. See some Yamaha V twin heads and barrels with bosses for cam chain adjusters moulded on both sides of the barrel tunnel. The choices of can driven by belts or chains can also add choices of head, distances and other parameters. If the cam chain needs to be longer or shorter, they can be modified and re-assembled. Cam belts if over length, can simply move around another roller to adjust the length, as these belts can be used in some quite contorted paths.
Two different cylinder heads, both doing the same thing and offering a useful insight to both design and it's continual evolution.

Another useful aspect of design is whether the original alternator and clutch covers can be integrated to fit the new design of crankcases, as they often get used with minimal modification. Only with oil galleries in clutch covers will there be any need to rethink the oil routes.

When making patterns for crankcases, the thinner outer cases are more difficult to cast, and these can be separate components. In many designs, it may be recommended to make the core crankcases, then add just the upper and lower case walls. In some cases, it may be preferable to leave these open and weld in sheets after casting. With plumbing, the oil feeds to the various places are often copper pipes which are push fits into the casing, then swaged into position similar to boiler pipes and the whole then machined to take the bearings and cylinder mounting faces.

If an off road machine, or expecting to throw chains regularly, then thicken and rib the area where the chain can damage the cases and ensure a broken chain can be dumped easily onto the ground rather than bunch up and wrap around the sprocket area.

When modifying engines the directions of vibrations will change and the use of larger holes for adjustable rubber engine mounts may be preferable. The internal rubber bushes can be compressed with nuts and washers on the mounting bolt for development purposes, until the vibrations are at the best compromise values. If in doubt, some rubber bushes can be mounted in the frame, but this is rare.

Simpler designs of crankcases can allow copper, steel or composite lubrication piping to be inserted into the structure and the pressure side of the lubrication system to be minimised. This is often to three crankshaft bearings, or five via a gallery. The plumbing is easily modelled with tubes, plus the routings for the cylinder head transport and also the gearbox. The gearbox usually has lubricant to the insides of the shafts via end feeds, but this usually means a cross over shaft when using modern gearbox layouts. The output shaft usually has a well-shaped trap behind the clutch with a small feeder into the shaft. When designing and making your own crankcases, the options are unlimited. In some cases, just the upper crank case may be needed, the rest secured with split bearing holders. In such cases, the crankcase can be part of the chassis for ultra-light machines.
Engine oil drainage and sump design will depend upon the uses for which the engine is to be used. For racing, the sump should be deep, wide and short fore to aft. The Ducati V sump shows how a bike that wheelies a lot should be designed. For touring, a cool running engine is often preferred, but in cold climates, this can be problematic.
With the advantages of composite skins, the sump can be a partial dry type, with the lower part being like a drain area, so the reservoir is separate from the engine to reduce drag and ensure the supply is constant at all angles of the bike.
Drive to the choice of pumps is only limited by the options available, but usually the original pump used in the original manner, although a secondary scavenge pump can be added with a shaft extension and simply using two trocoid sets of internals used to double the scavenge part of the system, should room permit. Electric pumps can be used, but are rare, although electric scavenge pumps make it easier to change lightly modified standard engines into dry sump designs.

Likewise, cassette gearboxes are now possible. Easy change clutches using car components, as per the BSA Rocket Three can also be considered external of the oil systems. This makes advanced endurance racing machines a much more adaptable form, as proposed in various studies.

Making the patterns.
When making patterns, contraction is a major concern. Pattern makers have an unusual ruler. It contains slightly enlarged scales for different materials, as when the metal is cast, it will then cool and contract slightly. This may only be a few percent, but for the best designs, this must be taken into account. The modern die cast production motorcycle components such as crankcases and wheels allow much finer metals than is possible in ordinary foundries. Therefore sand casting and contraction is part of the design of most non-commercial pattern making.

The other main aspect of making patterns is that they must be removable. This is a bit of a jigsaw puzzle, and any obscurely blocked or hidden holes or areas must be made as secondary, removable parts. Traditionally these are painted black, as compared to the varnished wood of the pattern.
When a difficult pattern is needed, then the patterns can be made from white or blue foam, such that it can remain in the sand mould. When the molten metal is poured in, the foam dissolves and is removed as vapour, but this must have suitably well designed risers.

Almost all patterns are made from wood. Easily carved wood is preferred, for obvious reasons, plus stability for years, as they may be needed again, so old or well seasoned wood is preferred. Crankcases which have hollow areas will need internal patterns, but for simple upper and lower casings, a matched pair should suffice. The pair will meet on a flat machined face, so each crankcase can be carved from just above this plane. Where inaccuracies in the casting are made later, they can often be solved with a little alloy welding.

I prefer to build up my patterns from a central datum, such as the joint face of a crankcase set. This allows the pattern to be build up on the flat surface of the mould join which is also the main engine joint face, for example, with a horizontally split crankcase. I use a piece of plywood as the working face, with the main bearing and gearbox supports made first, but mounted a few millimetres higher to allow for machining. Then the interlinking strengthening ribs, and outer faces for the alternator, starter motor and clutch cover and such like. Then the oil lines supports. Finally the details and the filler to make a taper fit, to ensure this will all pull cleanly out of the sand. Then the base plate removed to leave the basic pattern. Where hidden areas must be made, these are carved to fit snugly with the pattern, to prevent sand getting in the gaps, and to ensure smooth moulding curves.

Carve the model of the crankcase basics first, but leave it oversize. This may require a few pieces of wood which must be very securely made. Then add any webs and fillets, which can be glued in place then carved to size and appropriate shape for improving molten metal flow.
Take note to allow extra material for machining processes. Ensure the liquid alloy will be allowed to flow down through a side part of the casting, so that the flow to all parts will not be obstructed. Where small or fine areas are to be cast, they must include an extra flow off section, to allow the molten metal to penetrate fully into such areas. The extremities are particularly prone to voids. The cooling metal will shrink as it cools while still molten, and any area prone to shrinkage must be close to the inlet pipe and the excess risers. The risers should be at suitably placed areas, to encourage full and clean molten flow. If in doubt, add more metal in the design, as this can be removed later.
The pattern must be capable of being moulded, then removed cleanly. This demands no hidden faces. Also demands a slight tapering of the profiles to allow easy removal of the pattern without damaging the mould. There is a lot of subtlety involved in making patterns, so if in doubt, try making a mould with it in the kiddies sand pit, then modify until it makes a cleanly removable, usable pattern. As most crankcases are split along a single plane, often horizontally, then the upper half of the mould will usually be a flat block of sand with just the downers and risers carved to allow the molten metal to flow.
The pattern is laid on a flat surface, dusted to aid release and the casting container placed over it. Then lightly resined sand is applied followed by bulking sand which is all hammered down compactly. When solid, the mould is scraped level, and turned over. The pattern has a spike hammered lightly into it to loosen it from the sand, and to cleanly remove the pattern. If a matching upper half of the pattern is to be used, then the upper pattern is placed on the lower pattern using alignment dowels, then dusted, the upper mould casing aligned and clamped, then similar sand applied and compacted. These will then split cleanly, the patterns removed, downers and riders carved into the sand, possibly some setting gas to cure the sand. Then any dissolvable cores or specialist sand cores added, reassembled then warmed thoroughly to remove any traces of moisture.
Therefore if making a complex pattern which protrudes into both the lower and upper halves of the sand moulding box, then the pattern must also be cut in this horizontal plane, joined with a few alignment pegs, then carved to a prefect finish. This will allow the lower half to be moulded first, then the upper half of the pattern positioned on the lower half, dusted then the upper half of the sand mould added and when compacted, can be lifted off to permit the pattern halves to be removed.
The shape of the pattern is first carved, then painted smooth to allow easy removal from the sand. The downers and risers will be decided by the foundry staff, who will carve these holes in the sand as they deem fit. The foundry staff will tell you if the pattern is suitable. Most modern alloy castings are cleanly poured, with no porosity. The casting of finer areas is now possible with improved techniques and materials. If in doubt about the alloy mix, then ask first, then check, but a suitable rule of thumb safety margin compared with similar designs is often acceptable.
One set of wooden patterns can make infinite number of moulds, but in a few cases, high density white polystyrene shapes can be sacrificially integrated into the mould, which are mostly dissolved away by the molten metal. If used, the polystyrene must be capable of retaining its shape as the sand is compacted around it, and also be capable of being supported accurately in the sand mould. The supporting areas are usually marked with black areas, to represent where they are supported in the sand relative to the mould. Where gas cured sand moulds are used, then the polystyrene may not need to be so compact resistant.
The foundry will probably schedule the casting with others using the same materials, so a wait of a few days or weeks is to be expected. If in doubt, or cannot afford delays should machining go wrong, budget for a couple of sets of castings.
The pattern will be returned with a spike mark in it, as this is how they are removed without damaging the resin and sand mould.
First clean the castings fully, but without brushing the surface too hard. Sand blasting is often done in foundries. Inspect with minute care, looking for porosity and failure to fill all areas of the mould. Discard if any faults, then redesign for better casting. Return the old castings to the foundry to be recycled.

Machining.
Unless using standard gasket materials, it is recommended to not use gaskets between crank cases, so that the measurements do not change which maintain accurate alignment. In some cases, the use of different thicknesses of gasket materials and / or shims can help reduce the problems from machining inaccuracies.
Misalignment axially between clutch and final drive can be much less than the fine tolerances between the crank and clutch shaft holes, which must ensure perfect gear lash. Some engines are supplied with different crank and clutch gears with lash numbers for later adjustment, but accurate machining is preferable, especially with straight cut drive gears.
Before machining, any inserts should be welded into place, such as upper and lower casing sheets. Then any heat treatment to remove inherent stresses.
The two halves must now be mated, usually by flycutting on a milling machine. But a skilled engine fitter can file flat, rubbed on abrasive paper on a flat surface, then scraped with marking blue on a face plate or plate glass sheet. Hand fitting should not be sniffed at, as it can be just as good as the best. Start off with a millenicut file then work down to smoother files using chalk rubbed on the files to prevent clogging by alloy. If hand fitting when scraped to a good fit or if flycut with clamping forces involved, it is recommended to lightly lap the faces together with fine grinding paste.
If flycutting, first place crankcase joint face down, then flycut at least three level clamping points on the opposite face, so that when turned upright, the flycutter will have a good plane to approach, parallel to the main face.
Then the two halves are aligned and two small dowels fitted to maintain alignment. Fit the first blind dowel, then line-drill the other. Some commercial crankcases show such holes on the outside flanges near the rear engine mounts, but a couple of hollow sleeves concentric with securing bolts is better, possibly used as part of an oil passage with a sleeve dowel. These are then clamped together by drilling and tapping the various mounting holes as required. They should be torqued to about half the working torque of the final engine, as this gives an extra little pinch to the final fit of the bearings as the casings are torqued fully.
It is very important to fit as many of the mounting bolts and studs prior to machining. This may require some hand fitting and filing to create the bolt mounting faces. The crankshaft bearing holes will now need to be line bored, and this is the work of professionals. As the crank and gearbox shafts have to perfectly aligned, it may be worth setting up with the original crankcases on a milling machine to check the cutting positions, then replacing with the new castings. (For those with hand operated machines, adding digital readouts is fairly easy for all three axes.) For line boring the five crank bearings, it may be possible to buy, borrow or hire an adjustable reamer, then add extensions to maintain its accuracy though the casings. In some cases, it is possible to use the same tool for vertically re-boring barrels. At home, a pillar drill helps greatly for vertical holes, but only if it has decent head bearings. If a fly cutter is available, then this can also help for some milling and face work. If using the cross slide of an old lathe or mill, always check for play first and adjust carefully. An old lathe or small mill can still work well if maintained well.
With the cases secure, the various shaft and bearing holes can be bored to the same dimensions as the original component. These are now a matched pair. This usually has the crankcases on a vertical face plate for ease of milling. It is imperative to ensure any gear driven primary drive has absolutely perfect measurements between crank and primary gearbox or clutch layshaft. If in doubt, consider engines with chain or belt primary drive. All parallel shafts holes should ideally be machined at the same time. Measure the original crankcases accurately, as compound inaccuracies can occur.
Once the crank holes are line bored, the web faces to limit side float can be machined where required. Likewise any bearing circlip slots before removal from the machine. Where possible, immediately after line boring the crank and gearbox bearing holes, the clamped crankcases may be able to be rotated on the base mounting to machine the barrel base without loosing parallelism from the crankshaft alignment. This usually requires a rotating or angled mill head. This need not be anything more than a precision flat face at this stage, with the barrel holes machined later, aligned by the cam drive and piston side play. Compression ratio can be slightly adjusted with this machining operation, if it does not upset the cam chain tension. As the home builder will probably be using a standard or modified crank, then simple fitting skills can be used. The old shells used to allow alignment and any oil galleries and grooves carved carefully with a small modellers hand grinder.

The clutch and alternator cover faces can now be machined, although if not too sure at this stage about final alignment, with lightly modified or standard casings, this can be done later by hand.
The alternator cover face can be flycut, and the alternator and its cover fitted with shims between the rotor and stator, to allow the accurate alignment of drill holes for the locating dowels to ensure an efficient alternator air gap for generation.

Mounting the starter motor can begin with deconstructing the motor and using the intermediate shaft with the end of the shaft machines slightly with a central pip, so the gear can be placed on the alternator then the shaft positioned on the crankcase. A drill the same diameter as the shaft is then used to line drill the correct position using the gear to ensure correct lash. Then the armature is then used to align the motor mounting holes to the intermediate gear, then likewise drilled then opened out to a good fit. Then the motor body can be aligned and then the end bolts fitted for good alignment and the mounting bolt holes drilled to fit. If using fancy cutting machines, then this is more easily done with careful measurement tools fitted to CNC machines. Electric starter motors can be positioned anywhere around the starter ring so they can be conveniently placed for easier maintenance especially on a dry sump machine.

When deciding to do your own machining, plan the sequence very carefully, so that inaccuracies in misalignment are minimised. Placing the assembled crankcases on a large metal cube will help it retain alignment to the drilling and machining surface. Likewise accurate spirit levels and other devices and techniques of pragmatic engineers can make a particularly good and accurately machined set of cases.

After machining, the castings are inspected for any flaws revealed by this metal removal. Then cleaned up and the various oil holes drilled and then the crank shell or roller bearings and crank fitted, which allows the oil pump to be placed into position and drilled for perfect alignment to the drive gear or chain and sprocket. Then the oil pump inlet and exit galleries machined and dressed out with a hand grinder, often using the gasket as a guide.
It is quite common for a long drilled hole for an oil gallery to cause problems by breaking the surface of a casting, or to get too close to the surface to guarantee reliability. In such cases, the best solution is to drill a little larger and insert a steel or brass or copper tube. In some cases where the routing is not a blind hole and using annealed copper or thin wall brass which is of a suitable internal diameter, then a ball bearing or similar item can be forced down the pipe to swage the pipe into a perfect fit into the drill hole. These can then be drilled to feed the crank bearings or as appropriate. If no ball of suitable diameter, a polished steel plug can be used. Don't force this too much.
For blind holes, the drill can be drilled fully through to check alignment, then a ball bearing press fitted in the end. In most cases, it is far better to screw thread a plug, then use machinery adhesive, especially on high pressure oil routes as used for shell bearing engines.
Use high temp silver solder on any copper pipe joins. Bronze weld (hard solder) any steel pipework. All press fit pipes should also have a bolt fixing to ensure security, especially on the pressure supply.
Where clutch covers or cylinder bases must align for oil flow, it is very useful to use a blank paper gasket as a primary guide to check correct alignment and ensure adequate oil flow. Many custom and racing engines use external oil lines for convenience of casting and machining. If any weight of external oil pipes and fittings is not used, the extra weight used in making the oil galleries integral in the crankcases will help make a more rigid set of crankcases and add reliability.
Then the crank cases can be split and main shell oil ways drilled through, the shells and crank and pistons fitted for checking bearing clearance tolerances. Always scrupulously clean and de-burr these areas as they must supply particle-free oil to the major bearing groups.
With the crank and pistons in place, the barrel can be fitted and used to align the barrel to the piston(s). This may be simply fitting the con rods and pistons, sliding on the barrels, then checking the float on each side of the piston, placing the base of the barrel on the cylinder base face and marking the middle point. Then check the cam chain alignment. With the barrel aligned with the piston, the barrel openings can be scribed and carefully dressed to fit by hand. When the barrel can fit down to the crankcases, the stud holes and oil ways can be marked. As mentioned when building bike frames, the engine also should be approached using the correct hierarchy of the components. Then the cam chain guide positioned and the cam chain tunnel can be dressed appropriately. A base gasket makes a superb profile guide.

Engine Hierarchy.
When building an engine, the engine fitter should approach the components in the correct manner. The crankshaft is usually the core alignment component. From this radiates the transmission system. This usually demands correct alignment of the clutch and then the gearbox. From the crankshaft also radiates the conrods and pistons, which decide the alignment of the barrels, then the cylinder head.
As can be realised, the components are aligned to the more important alignment components. For example, barrels can be fitted over the pistons, then this is used to align the barrels laterally to centralise end float. The cylinder barrel and head studs are then drilled after the barrels are seating accurately. Later on, after assembly and running, the barrels may be giving inaccurate piston wear, so the faces may be scraped to ensure perfect piston alignment. This is all part of fitting an engine. An engine fitter is not just a mechanic, but a detective and a craftsman.

Once the basic crankcases are made, the castings can be dressed and refined to ensure the correct oil flow regime throughout the engine.
From the pump, the oil flows to the filter. This is a paper element for engines with shell bearings. It is common to add a possibility of a cooler after the filter. It flows more easily through paper before being cooled. An external disposable oil filter canister also helps cooling.
The shell and plain bearings take the first priority and must maintain correct pressure. This may also include any camshafts running in the cylinder head or elsewhere. Then the lower pressure bearings can be fed via restrictors to maintain primary pressure to the important bearings. Restrictors should preferably be pointing upwards, so that residue does not block them.
For simple, adjustable restrictors, the use of the very old technique of fitting a larger restrictor such as a drilled out main jet, then adding an adjustable number of fine wires though the restrictor to attain the required flow. It also has the advantage of being partially self cleaning, as the loose wires will help to unblock any small particles. Wire brush strands are ideal. This is also fail safe, as an escaped wire will increase the flow. The wire must be shaped so that a broken one will not be able to be transported to the bearing. This is an old technique from the steam age, but still applied on some research engines to vary camshaft oil flow. Clamping or crimping a pipe to restrict flow is never done, as it can cause blockage unless well filtered and is not easily adjusted. In some cases, it is possible to fit a screw adjuster, but this is rarely necessary unless unusual problems occur.
It is not uncommon for external oil lines to be adapted to cylinder head oil galleries, which often use banjo bolts to external connections to oilways in the head.

Oil levels are usually checked with a low oil level warning switch or a sight glass, upper level drain hole or dip stick. Where a clutch cover retaining screw is at the same level, it's internal boss can be partially removed, so the oil can flow out when the screw is removed, acting as a primitive level indicator.

Testing the new cases.
First check after full assembly is with the spark plugs out and cranking to check basic oil flow. An electric motor can suffice, or turning the clutch or alternator by hand. Then fitting a vee pulley to the alternator end, and using an electric washing machine motor to check the working oil pressures and oil flow rates. After these primary tests, all wear marks can be assessed and possibly checked with engineers blue on the various shells, piston flanks and other mating areas, with particular care on the primary drive and gearbox meshing. Also check any hydraulic tappets. When settled, some ultra precise machines may require checking crankshaft deflections, but is rare if heat treated before machining and line bored.
At tickover speeds, oil flow rates can then be checked, then the pressure.

Then the first run using petrol, to check oil level as the engine runs. Again, oil pressure checks while running. An oil pressure gauge and warning light is important.
Full load on the whole engine is not possible statically, but engaging the rear brake or an equivalent as a load can give some lower rev, high throttle openings to check cylinder head, main bearings and other high load areas, including mountings. Then high revs with lower throttle openings to check vibrations. It will be noticed that imbalance may well occur and is acceptable, or any rubber engine mounts may need tuning.
Thermal distortion while running may cause leaks or other problems, but not likely. Where the crank cases leak due to porous metal castings, the inside can be scrupulously cleaned and painted with high temperature, oil resistant epoxy resin. It is dangerous to have porous castings, as these are potential fracture zones and if problems present themselves they should only be for testing while new castings are prepared. This is rare with the newer free-flowing casting metals. If problems persist, consider machining from solid billet cases. Solid billets can be heat treated then press forged to a close shape, ensuring the grain structure of a powerful engine is a good as is possible.
Cam lubrication and its drive adjustment must be constantly checked for excess wear or poor lubrication.

Long term problems from frame and engine fracturing can be a problem, but long term testing is often only possible from expensive equipment. The engine can be mounted in a metal stub frame or jig, then run through a good thrashing for a few days. This may need a dynamometer, or one or more large car disc brakes with new pads, or a water brake is possible, but under study at present. More funding required. See also testing on companion monographs.

The way a modified engine fits into frame is also a problem. Rubber mounting will help, but may not solve all problems. Cylinder head mounts to the frame must also be very carefully considered. Vibration problems with fixed or rubber mounted carbs may also be a problem, especially if it vibrates the fuel. Everything should work in harmony, preferably at different vibration amplitudes, so nothing gets out of control. Most imbalanced bike engines resolve much of the vibration to a horizontal vector, as this is more easily resolved into the bike frame and suspension. The vertical vibration component is usually discouraged to a fair degree to reduce frame flexing and for rider comfort reasons.
When the engine vibration is not ideal, the crank can be lightened by removal of safe areas of the crank webs, or made heavier with extra metal welded to the crank, or holes drilled and slugged with lead. The latter can be dangerous and needs careful design to prevent the lead from loosening. If in doubt, it is often best to use an engine with low primary vibration problems, such as the 90 degree vee twin, or to use engines with counter balance shafts, which can be more easily modified, but must be mounted correctly relative to the crank and piston movements.

Modifications to cranks, such as stroking and other mods are best left to the aftermarket suppliers who specialise in these areas. Likewise camshaft design and modifications, piston choices and barrels which are best sourced from aftermarket suppliers, often of racing components. If upgrading to racing components, use the old parts to test the engine prior to fitment of the expensive parts.
Reading the shell bearings after initial testing will indicate any distortion in important areas. Likewise engineers blue on drive trains will help check the cases or diagnose problems. During the strip down, the case faces can be checked for inherent distortion with engineers blue on a face plate or plate glass, to see how much they have distorted and where, then to figure out why. Perhaps the next size of shell bearings may be required after the settling in process, or perhaps other bearings may require a larger oil scoop or deflector.

For making barrels the manufacturing process is similar, but water cooling flow must be ensured. For multi cylinders in a bank, this should have centralised or end positioned coolant inlet and exit flow for even heat dispersion. This may require internal deflector plates or fins to prevent a cold spot at the inlet connection or hot spots in dead flow areas. It is not necessary to have full length barrel cooling, but just the upper half need be cooled. Many firms supply iron barrels either as wet liners or as permanent pressed-in inserts. For ultra light designs, it is possible to simply clamp the bare cast iron barrels between crankcase and cylinder head, then fit a minimalist water jacket around this, ensuring it works well with the cylinder head cooling flow.
In some cases, the coolant (and oil) flows through the cylinder head and the barrels can be separate to ease the engineering needs and allow very simple head gaskets. In some cases, head and base gaskets may not be needed. Try to use shouldered wet liners which can support the barrels part way up their length, allowing stronger crankcases.

If the above does not faze the reader, then a closer study can be done using specialist casting design and manufacturing sources, but this is a full subject in its own right.

Aerodynamics.
See aerodynamics on the same website.
Part 1: Without a wind tunnel: Aerodynamics. Reducing Drag. Wind. Particles. Clothing. Cotton tufts. Slime. Smoke probe. Pressure gauges. The no-tunnel wind tunnel.
Part 2: Wind tunnels: Wind tunnels. Test cell. Power. Propellers. Safety. Constraint. Balance. Data capture. Computers. Interfacing. Software. Sensors. Layout. Video. Fairings. Other uses. Scale models. Uses.

Recommended reading on this website.
For small scale manufacture, - see motorcycle mechanics advanced, on this website.
For ergonomics, - see composite HPV design, on this website.

Style.
No one should presume to tell the designer what the machine should look like, but asking as many and various people as possible will help decide if the rest of the world will also be able to come to terms with a radical machine.
Not all advances are welcome by everyone. What the salesman may consider exciting, to others may simply be a fools toy.
Application of electronics to many aspects of the riding experience is increasingly common and not always welcome. Unfortunately the application of electronics to increasingly important components can be worrying. From passive radios to interactive fuel injection and cruise controls to the important safety areas of brakes, fail safe is increasingly important. Be very careful when thinking what is applicable and put all non essential systems on separate fuses.

When designing a machine, consider trying to integrate the whole, so that a running motif or theme is applied across the whole machine. There are many, much better alternatives to chrome plating.
Anodising of small aluminium components can be easily done at home and a dye used for tinting the aluminium. It is much simpler than expected. Small parts can be anodised in a plastic cup using a battery charger, special salts and battery acid. Nylon can also be dyed.
If using computers, 3D graphics software with rendering makes the work supremely adaptable and helps refine the concept.

There are many ways to enhance a design, from anodising alloy fittings to advanced electronics. Please use and apply sensibly. Do not become a fashion victim. Always remember that so-called 'good taste' usually appears when imagination dies.

Science and technology can help, but the art form must grow from the dream, with inspiration to make it possible and occasionally that which makes all life worthwhile, the dream coming true just the way it's imagined or occasionally, even better.

All testing should be conducted with the intention of making the next machine even better.
An open approach to design will occasionally fail, but the failures will also lead towards better machines.
Please do not create anything which could bring motorcycles into disrepute.
Riding with a big grin can cause 'flies stuck in the teeth syndrome'.

Other.
Motorcycles have been with us for a century and show every chance of being even better in the future. (subject to blinkered corporate designers and blind buEUrocrats.) Never vote for lawyers or corruption in politics.

Whatever is done and whatever materials may be used today, the design has probably been done often centuries before.
Although many machines are wonderfully radical, there is nothing in this monograph which has not been done before and most standard applications of technology can be seen at any bike shop. It is the way ideas are combined which can often improve a design. The only difference is that this monograph may hopefully help to create a recipe that can make a very harmonious and refined riding experience suitable for the twenty-first century.

The above information is not the only way to make a machine. Everyone will have a different approach according to personal preferences and engineering and design backgrounds. Motorcycles are now having to come to terms with congested cities and being fashion accessories. Yet motorcycles are showing they can hold their own with the best, with scooters showing the general public the true convenience of two wheels, in a way applicable to most people. Motorcycles of all forms are now beginning to leave the infancy of their development, but all innovation can help produce better machines.

Innovation is a wonderful and often the definitive approach to design, but a learning curve for craftsmen is needed before an excellent machine is crafted. For artists and visionaries who dream much further than most, this may involve a lifetime to develop and ride total creative freedom.

It is hoped that the above has not encouraged the reader to think that building machines is expensive. It is not.
Being able to use your hands and brains is sufficient, but the design can be improved by making the most of what is available, especially if on a tight budget. This monograph has hopefully shown that ordinary people with few tools and small budgets can also make the best.
Not all readers will be able to develop machines to the fullest extent, as cost is rarely the main limitation. Time and effort are usually the worst offenders, with time being needed to build up the skills required. This is a long term process and enthusiasm is important. It is hoped that this monograph has offered enough encouragement for the reader to venture forth in a positive manner.
Much of the componentry is up for grabs at little or no cost. Finding and discovering new materials and componentry should be considered as part of the innovation process for those whose self respect can handle it.
In a world of increasing gap between rich and poor, where many have no idea nor inclination how to fix a fuse. So it is usually the intelligent poor who have most to gain, being able to understand the problems first hand. This gives a nice selection of slightly older, still useful equipment to be recycled for use. Being free, it is easy to attempt things never considered with other equipment.
As many good ideas sink without trace, compare the history of innovation of professionals with those of 'amateurs' to understand the social implications. It is but one easy step for many people to also veer away from normal routes of working and understanding the world of technology and design.
If you are a Brit with a good idea, then always go abroad and develop it, as Britain is a dead end for innovators. The government may want more innovators, but you are always better in Oz, or in the evil USA.

Repair by replacement should be discouraged, as the fundamentals always count.
In the modern world, most high tech items are discarded despite being perfectly serviceable. This is due to the increasing inability to educate hands-on engineers, (which infuriates the author) as ability to pass exams erodes the ability to do real work. This is well documented in many excellent articles on the subject. Therefore the modern engineer is evolving to a parts replacer, where the ability to diagnose from basic principles is no longer needed, simply plugging in the diagnostics box and replacing the component. This often seems efficient on paper, and gives the resourceful innovator an excellent source of componentry if the discard point is targeted. Do not be afraid to be a much better engineer than this.

From the many machines, wheels discarded due to lack of wheel builders, to videos and computers for similar reasons, the world is awash with excellent equipment for free. Always become fri