Under-inflation has caused this tyre to wear on the outer edges of the tread, leaving the central tread area far less.
Over-inflation has resulted in the central tread area being forced into contact with theroad causing rapid centre and worn shoulders.
A typical example of the wear pattern caused by front wheel mis-alignment. (Toe-in or toe-out) The edge of the tread is “feathered” and worn progressively from one side. The wear ridges can be felt by drawing a hand across the tread.
Excessive wheel camber has caused sloping wear on the outer edge of the tread on one shoulder of this tyre.
This tyre has been used well after reaching the legal minimum pattern depth of 1.6mm.
End of life
This tyre has reached the legal minimum pattern depth of 1.6mm.
An emergency braking manoeuvre with this tyre has caused the tyre to rapidly wear through the complete casing causing the tyre to deflate.
Sharp objects can cause considerable damage rendering a tyre unserviceable.
This is damage caused by an impact to the sidewall. The bulge or “egg” ndicates localised casing damage.
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.
Surveys by 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).
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).
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.
Proper care and maintenance of tyres will reward drivers and vehicle owners with greater safety, better road holding, more comfort and, ultimately, savings in cost. It will also save them from the risk of severe penalty (i.e. fines and driving licence penalty points) should they be caught on the road with tyres which do not conform to legal requirements.
This section explains the main legal requirements for the condition and maintenance of tyres, and gives advice on tyre care to achieve longer life and lower operating cost.
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:
1. Tyres must be suitable (i.e. of the correct type 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).
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.
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 of tread+ and in a continuous band around the entire circumference of the tyre. * For goods vehicles over 3.5 tonnes the minimum tread depth requirement remains at 1mm (along with other requirements). + Breadth of tread means the width of that part of the tyre which is in contact with the road surface under normal conditions.
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 tyre or the wheel to which it is fitted must be of a different colour to the other wheels on the vehicle and a label must be attached to the wheel giving clear information about the precautions to be observed when it is being used.
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.
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 a misleading pressure reading 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.)
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 they are 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.