Tyre Basics
or Tires for our American friends
Ok, so apart from looking good you want your Mondeo to out accelerate every
Clio on the road, Out corner all the Pugs and out brake a Skyline. So you spend
time on money on the engine, suspension and braking systems, and then you go to
Kwik Fit for the Tyres !!!!!
It is a fact of life that Tyres are probably the item singly most responsible
for our cars handling. They have to work when cold, hot, wet, brand new, old,
covered in mud, grit and oil and still last as long as possible.
Here in Europe the trend is for tyres with a higher coefficient of friction,
advanced wet weather performance and dry performance, whereas in the States the
emphasis is on long life, hence you see tyres there guaranteed for 80k miles or
the life of the car (they are like lumps of concrete!!). In fact tyre design has
come a long way and even the worst tyres today are better than good tyres of 10
years ago.
Of course American tyres are also designed so that the whole car explodes in
a large spectacular fireball as they leave the ground (Shortly after the hubcaps
shoot off on a fast corner), see any Hollywood film for proof
What most people want to now is what tyres will fit on their cars. To help
with this I have written the Mondeo Tyre Sizer Program
There are some other things you must know about them (mostly stolen from Dunlops
web site www.dunloptyres.co.uk,
Goodyears Site www.goodyear.com and
Yokohama's site www.yokohamatire.com)
What the law
requires
It is important to understand what the law requires in regard to the
condition and care of tyres. Regulations govern many aspects of tyre condition
of which the following are the principal points, correct as on June 2001.
1. Tyres must be suitable (ie of the correct specification and size) for the use
to which the vehicle is being put and must be inflated to the vehicle or tyre
manufacturers' recommended pressures.
2. Tyres of different types must not be fitted to opposite wheels of the vehicle
(for example, radial-ply tyres must not be fitted to a wheel on the same axle as
wheels already fitted with cross-ply tyres and vice versa, and a two-axle
vehicle with single rear wheels must not have radial ply tyres on the
front axle if cross ply tyres are fitted to the rear axle). (I will add that
only a prat would put different tyres on either end of the same axle, Always
replace tyres in pairs so they are the same make, model and tread depth or you
wont skid in a straight line)
3. No tyre must have a break in its fabric or a cut deep enough to reach the
body cords. No cut must be more than 25mm or 10 per cent of the tyre's section
width in length, whichever is the greater.
4. There must be no lump, bulge or tear caused by separation or partial fracture
of its structure, neither must any portion of the ply or cord structure be
exposed.
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Minimum tread
depth
Tyres on cars, light vans (not exceeding 3,500kg gross weight) and light
trailers must have a tread depth of at least 1.6mm across the central
three-quarters of the breadth+ and in a continuous band around the entire
circumference of the tyre. (and I would add that below 2mm of tread, wet weather
performance drop considerably so change em!)
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Run-flat
and temporary use spare tyres
Regulations permit the legal use of 'run-flat' tyres (provided they are
identified as such) in a partially inflated or flat condition, and what are
described as temporary use spare tyres. When a temporary use spare tyre is being
used, the vehicle speed must not exceed 50mph, and a special high inflation
pressure is normally used, otherwise the legal provision which permits their use
ceases to apply. The temporary use spare must have a label of different colour
attached to the wheel giving clear information about the precautions to be
observed when it is being used.
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Offences
The use of a vehicle on the road with defective (or incorrectly inflated) tyres
can result in prosecution for which the penalties are heavy. Maximum fines for
such offences are now set at level 4 on the standard scale, namely £2,500 for
each offending tyre (£5,000 if committed with a goods vehicle) and the driver's
licence will be endorsed with 3 penalty points. If the offences result in danger
to other road users, heavier penalties and driving licence disqualification may
follow.
A random survey by the police and the Tyre Industry Council recently showed that
there may be as many as 12 million illegal tyres in use on vehicles in Great
Britain.
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Tyre care
The essential ingredient for keeping tyres in good condition, to provide optimum
performance and give maximum life is air. It is air that keeps tyres fit and
safe and carries the weight of the vehicle and its load, not the rubber or the
casing material.
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Tyre
care at home or in the garage
Tyres should be checked regularly either
at home or when visiting a garage or filling station. Particularly, prior to any
journey they should be examined for obvious signs of under-inflation, wear, cuts
in the tread or sidewalls, bulges in the sidewalls and stones and foreign
objects trapped in the tread grooves (which should be removed). It is useful to
check for leakage at the valves (especially following inflation) and to replace
missing valve caps. A small tool can be obtained to check remaining tread depth.
If the tyres show any sign of uneven wear the vehicle should be checked to
ensure correct alignment and balance of the wheels.
Tyre pressures should not be checked during or immediately after a journey while
the tyres are still warm. This will result in an incorrect pressure reading.
(NB: It is worth investing just a few pounds in a pencil-type, pocket tyre gauge
so you can check pressures regularly - unfortunately some garage forecourt
gauges suffer abuse and may give misleading pressure indications).
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Tyre
maintenance check list
Tyres will provide greater life if they
are properly maintained - it is an inexpensive task which takes only a few
minutes at regular intervals. The following Check List will be helpful in this
task:
1. Check the correct pressures against the manufacturer's recommendations as
given in the vehicle Handbook.
2. Adjust pressures as necessary.
3. Clean dirt from valves and fit valve caps all round.
4. Remove stones and other foreign objects from treads.
5. Have the steering alignment corrected if front tyres show signs of excessive
or uneven wear.
6. Examine brakes if tyres show signs of wear through wheel locking.
7. Have front wheels and tyres balanced if there are signs of vibration, wheel
wobble or patchy tyre wear.
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Tyre care on
the road
The way in which a car is driven can
contribute to excessive tyre wear and damage. For example, not adjusting the
pressures when the car (or van) is fully laden or when driven at high speeds are
major contributors. The following additional advice will help to protect your
tyres:
1. When undertaking long journeys, especially at speed on motorways, examine the
tyres both before and during the journey (but do not check pressures while the
tyres are warm).
2. Avoid harsh braking, fierce acceleration and fast cornering (the steering
wheel of cars with power-steering should not be turned while the car is
stationary).
3. Avoid driving over or scrubbing against kerb edgings or other raised
obstructions.
4. If it is absolutely necessary to drive over rough, uneven, unmade ground or
over ground littered with debris, check the tyres soon afterwards to ensure that
no foreign objects have become trapped in the tread patterns and examine the
sidewalls for cuts or bulges.
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Avoiding tyre
troubles
There are many individual causes of tyre
troubles. However, the three abuses which will cause most problems, and the
greatest costs, are under-inflation, overloading and speeding.
Under-inflation
Surveys by Dunlop Tyres Ltd, tyre service
engineers show that at least 25 per cent of all tyres examined are
under-inflated by more than 10 per cent. Neglect of inflation pressures is one
of the principle causes of rapid shoulder wear, uneven tread wear and premature
tyre failure and it is an abuse which surveys show to be on the increase. (NB:
It should be stressed that over-inflation may also result in inferior vehicle
handling, excessive tyre wear and premature failure).
Overloading
Loading cars, light vans and lightweight
trailers above what they are designed to carry is illegal. It is also likely to
put excessive strain on the tyres resulting in greater than normal deflection
and overheating which, in turn, leads to more rapid wear, greater susceptibility
to impact damage and the danger of premature failure. (NB: The vehicle Handbook
will give increased inflation pressures for full load conditions).
Speeding
Travelling for long distances on motorways at
sustained high speeds and generally exceeding statutory speed limits imposes
strenuous demands on tyres especially in terms of heat generation. Tyres in good
condition and correctly inflated are designed to withstand the heat build-up at
their maximum rated speeds. However, if inflation pressures are significantly
below those recommended then excessive heat will be generated, and in
consequence wear will be accelerated and deflection will be greater with the
risk of premature, and sometimes catastrophic, failure.
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Hints when
buying tyres
Tyre suppliers commit an offence if they
sell a passenger car radial ply tyre which does not have an 'E' mark showing
that it complies with the load and speed requirements of ECE regulations. With
certain exemptions (ie tyres for pre-1949 vehicles and for off-road and
competition use), from 1 January 1997 new car and light trailer tyres (including
'VR' and 'ZR' radials) must be ECE or EU approved and 'E' or 'e' marked
respectively (and from 1 June 1997 for motorcycle tyres).
Since 1 January 1995 it has been illegal for any person to supply re-treaded
tyres unless they are marked to indicate compliance with the current BS AU 144
standard. It is also illegal for any person to supply a part-worn tyre which
does not comply with legal requirements and which does not have tread grooves at
least 2mm deep
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How
much air should I put in my tires?
Proper inflation is the single most
important part of tire care. The inflation pressure on the side of the tire is
the MAXIMUM operating pressure. It is not necessarily the right inflation for
your vehicle. Always use the inflation recommended by the vehicle manufacturer.
You can find it in your owner's manual, posted on the edge of the driver's door,
on a door post or on the inside of the glovebox door. Always check inflation
when tires are COLD: when the vehicle has been driven less than a mile or one
hour or more after driving. Use a good quality tire gauge. Note: It's natural
for radial tires to have a slight bulge in the sidewall at their proper
inflation pressure. Check or adjust inflation every few weeks, before any long
trip or if traveling with a heavy load. And don't forget to check the spare.
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Should
I rotate my tires?
Regular and proper tire rotation promotes more uniform wear for all of the tires
on a vehicle. All
season tires should be rotated in a "modified X" pattern, meaning only
the tires being moved to the drive axle are crossed to the opposite side of the
vehicle. The remaining two tires are moved from the drive axle to the free
rolling axle, remaining on the same side of the vehicle. This method of
rotation helps promote a more even and uniform treadwear pattern for all four
tires.
The only exception to this would be the use of "directional" tread
design tires. These tires would remain on the same side of the vehicle and be
rotated straight forward and straight back.
If you have a four-wheel drive vehicle, we recommend crossing both pairs of
tires to their new axle positions.
We recommend tire rotation at least every 6,000 miles. Four-wheel drive vehicles
may require rotation even sooner such as every 4,000 miles. Check your vehicle
owner's manual for the manufacturer's rotation recommendations. If no rotation
period is specified, tires should be rotated every 6,000 to 8,000 miles. The
first rotation is the most important. When tires are rotated, inflation
pressures must be adjusted to the vehicle manufacturer's recommendations. Uneven
tire wear may also be due to misalignment or mechanical problems.
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Why
do my tires need to be balanced?
Properly balanced tires are important for driving comfort and long tire
life. Unbalanced tires can cause vibration, resulting in driver
fatigue, premature tire wear and unnecessary wear to your vehicle's
suspension. Tires should be balanced when they are mounted on wheels for
the first time or when they are remounted after repair. Tires should be
rebalanced at the first sign of vibration or "shimmy." Vibration
may also be due to misalignment or mechanical
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problems.
What
is alignment?
A vehicle is said to be properly aligned when all suspension and
steering components are sound and when the tire and wheel assemblies are
running straight and true. Proper alignment is necessary for even tread
wear and precise steering. Uneven front-or rear-tire wear, or changes in
your vehicle's handling or steering response (i.e. pulling to one side)
can indicate misalignment. Many vehicles today are equipped with rear
suspensions that can be adjusted for alignment. Your vehicle may need a
"front-end" alignment or a "four-wheel" alignment,
depending on the symptoms you are experiencing. The moderate cost of
having your vehicle aligned can more than pay for itself in tire mileage,
performance and comfort. Goodyear retailers provide expert alignment and
suspension service.
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Is
it safe to repair a flat tire?
If a tire loses all or most of its air pressure, it must be removed from
the wheel for a complete internal inspection to be sure it's not damaged.
Tires that are run even short distances while flat are often damaged
beyond repair. Most punctures, nail holes, or cuts up to 1/4 inch --
confined to the tread -- may be satisfactorily repaired by trained
personnel using industry-approved methods. Don't repair tires with
tread punctures larger than 1/4 inch, or any sidewall puncture.
Also, never repair tires which are worn below 1/16 inch tread depth.
Your best bet is to make sure your spare tire is always ready to do the
job. Check it regularly for proper air pressure and be sure that it is in
good shape. If your car is equipped with one of the several types of
temporary spares, be sure to check the spare tire's sidewall for the
correct inflation pressure, speed, and mileage limitations.
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Tyre
Specifications
There's a lot of useful information moulded
into the sidewall of a tyre. It shows the name of the tyre, its size, whether it
is tubeless or tube type, the tyre grade, speed rating, the maximum load,
maximum inflation, an important safety warning, and more.
P215/65R15 89H
Passenger
Tyre Sidewall Information
Example: P215/65R15 89H
"P" means this
is a passenger car tyre (as opposed to a tyre made for a truck or other
vehicle). P-metric is the U.S. version of a metric tire-sizing system.
"215" Section Width: The
width of the tyre in millimetres from sidewall to sidewall. This measurement
varies depending on the width of the rim to which the tyre is fitted: larger
on a wider rim, smaller on a narrow rim. The number on the side of tyre
indicates the width measured with the tyre fitted to the recommended rim
width.
"65" Aspect Ratio: The
ratio of height to width; this tyre's height is 65% of its width.
R" Construction: How the plies are constructed in the tyre carcass.
"R" means radial. "B" in place of the "R" means
the tyre is belted bias construction. "D" in place of the
"R" means diagonal bias construction.
"15" Rim Diameter: The diameter
of the wheel in inches.
"89" Load Index: This tyre has
an industry-standard maximum load of 1,279 lbs. Different numbers correspond
to different maximum loads. The maximum load is shown in lbs. (pounds) and in
kg (kilograms), and maximum pressure in PSI (pounds per square inch) and in
kPa (kilopascals). Kilograms and kilopascals are metric units of measurement.
"H"
Speed Rating: This tyre has an industry-standard maximum service speed of 130
mph. Tyres using an older European system carry the speed rating in the size
description: 215/65HR15. Different letters correspond to different
maximum service speeds.
The letters "DOT" certify
compliance with all applicable safety standards established by the U.S.
Department of Transportation (DOT). Adjacent to this is a tyre identification
or serial number; a combination of numbers and letters with up to 11 digits.
The sidewall also shows the type of cord and number of plies in the sidewall
and under the tread.
Tyre Grades: Uniform Tire Quality Grading System or
UTQG
Except for snow tires, the DOT requires the manufacturers to grade
passenger car tyres based on three performance factors: tread wear, traction,
and temperature resistance. The UTQG rating of each Goodyear passenger car and
light truck tyre is listed in the Car/Light Truck Tyre Catalog.
Tread Wear
· More Than 100 - Better
· 100 - Baseline
· Less Than 100 - Poorer
The tread wear grade is a comparative rating based on the wear rate of the
tyre when tested under controlled conditions on a specified government test
track. A tyre graded 200 would wear twice as long on the government test track
as one graded 100. Your actual tyre mileage depends upon the conditions of
their use and may vary due to driving habits, service practices, differences
in road characteristics and climate. Note: Tread wear grades are valid only
for comparisons within a manufacturer's product line. They are not valid for
comparisons between manufacturers.
Traction
· A - Best
· B - Intermediate
· C - Acceptable
Traction grades represent the tyre 's ability to stop on wet pavement as
measured under controlled conditions on specified government test surfaces of
asphalt and concrete. The Traction grade is based upon "straight
ahead" braking tests; it does not indicate cornering ability
Temperature
· A - Best.
· B - Intermediate
· C - Acceptable
Load Index and Speed Rating
The temperature grades represent the tyre's resistance to the generation of
heat when tested under controlled conditions on a specified indoor laboratory
test wheel. Sustained high temperatures can
cause the materials of the tyre to degenerate and thus reduce tyre life.
Excessive temperatures can lead to tyre failure. Federal law requires that all
tyres meet at least the minimal requirements of Grade C.
The speed rating is the maximum
service speed of a passenger car tyre. Light truck tyres are not speed rated.
Here is a list of rating indicators and their mile-per-hour equivalents. This
rating system applies to all tyre makers.
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