Tyres are the only parts of the car which are in contact with the road. Safety in acceleration, braking, steering and cornering all depend on a relatively small area of road contact. It is therefore of paramount importance that tyres should be maintained in good condition at all times and that when the time comes to change them the correct replacements are fitted.
The original tyres for a car are determined by joint consultation between the car and tyre manufacturers and take into account all aspects of operation. It is recommended that changes in tyre size or type should not be undertaken without seeking advice from the car or tyre manufacturers, as the effect on car handling, safety and clearances must be taken into account.
In some other European countries it is illegal to use replacements which differ in certain respects (e.g. size, load, and speed rating) from the tyre fitted originally by the vehicle manufacturer.
Types of tyre
Radial ply tyres are now the most common tyres in use on British roads representing more than 90%. Some radial ply tyres now have a run flat capability which are becoming more common particularly when fitted as an original equipment.
Radial ply tyres may be either steel or textile braced and are identified in the size marking by the letter “R” and often the word “Radial”.
Self-Supporting Run Flat (SST) tyres are designed to provide a limited run on period following a puncture. To be categorised as a run flat tyre, the minimum distance they must achieve in a run flat condition is 50 miles (80 km) at a maximum speed of 50 mph (80 km/h) and at a minimum of 80% of their maximum load capacity. It is essential the vehicle is equipped with a tyre pressure monitoring system to enable use of run flat tyres.
Do not mix tyre types
Except in the case of temporary use spare tyres supplied as original equipment, it is illegal in the United Kingdom and dangerous to mix tyres of different sizes on the same axle.
Temporary use spare tyres
Temporary use spare tyres are frequently a different size to the standard road tyres. Severe operating restrictions apply. Failure to observe the advice given in the vehicle handbook and/or on the tyre sidewall could have very serious consequences. Do not exceed 50 mph when using a temporary use spare tyre and observe the minimum inflation pressure.
Wheels and rims
It is essential the wheel size is an approved fitment for the tyre and vehicle concerned. Tyres must not be used on damaged, distorted or modified wheels since this could result in tyre damage, deflation and possible loss of control of the vehicle.
Removal and fitting of tyres
These operations should only be entrusted to a trained tyre specialist who has the necessary equipment and expertise. Inexpert fitting can result in injury and damage to tyres and wheels. Wheels should be balanced after tyres are fitted or replaced.
Valves
A new valve should be fitted when replacing tubeless tyres. When checking or adjusting inflation pressure, always ensure the valve is not leaking. A new cap of the sealing type should be fitted.
Directional and asymmetric tyres
Some tyres have patterns where their direction of rotation is important to achieve their full performance. These are known as ‘Directional’ pattern tyres and the direction of rotation is marked on the tyre’s sidewall.
Additionally some tyres have patterns which are different on the inner half of the tread than compared to the outer half. These tyres, known as ‘Asymmetric’, have their sidewalls marked ‘Outside’ and/or ‘Inside’ or similar wording. It is important with both these tyre types to observe the fitting markings on the tyre sidewall.
General Information
Driving over pot-holes, kerbs, speed humps etc even at low speed can result in the weakening or fracture of the tyre’s structure. It is dangerous to re-inflate a tyre which has been run flat or seriously under inflated and such tyres should be removed for complete examination by a tyre specialist.
Tyre manufacturers cannot be held responsible for problems arising from modifications to their products, or the use of sealants which they have not approved.