What's my tyre size?
There are three main numbers which go to make up your tyre size - the width of the tread (in millimetres), the height of the sidewall (as a percentage of the width of the tread) and the rim size (in inches).
Three numbers, three different units of measurement. Let's see if we can make that a little clearer. We might refer to a tyre size as 175/70/13, although your tyre may display the following markings: 175/70 R 13 82 T. This means:
- The tyre section width in millimetres (the width of the tread)
- The aspect ratio in % (the height of the sidewall divided by the tyre width)
- Denotes construction type - in this case a radial
- Rim diameter inches
- Load Index
- Speed Rating
What is the legal minimum tyre tread depth?
Car tyres, light vans and their trailers in Europe and the UK must have a minimum tread depth in the main grooves of 1.6mm over the central three quarters of the width of the tread. This must be continuous around the entire outer edge of the tyre.
Most car type tyres have tread wear indicators, usually at least six small ribs across the bottom of the main tread grooves, and when the tread surface becomes level with these ribs the tyre is at the legal limit and must be replaced. Simple and cheap gauges are also available to give an acceptable guide to tread depth.
What else should I watch for to keep my tyres legal?
Cuts, lumps, bulges or tears can all be caused whilst the vehicle is in daily use. Accidental "kerbing", over inflation of tyres, or off-road use of your vehicle can cause wear and damage. Regular checks will ensure you stay on the right side of the law, and continue to motor safely.
What does the law say about retreaded tyres?
All retreaded tyres supplied in the United Kingdom must comply with the British Standard for retreaded tyres, BS AU 144e, and must be marked with the Standard number (certain foreign made tyres may be acceptable if of an equivalent standard) At all stages they must meet the same load/speed performance standards as new tyres.
Should I buy second hand tyres?
The department of transport doesn't seem to think so. Here's a quote:
"There are many dangers in buying part-worn or ‘second hand’ tyres. Their history is unknown and they may have been removed from a vehicle involved in an accident or have been badly damaged by ‘kerbing’ or similar problems. Repairs may not have been carried out properly, for example to British Standard BS AU 159f."
What are the different types of tyre?
The two main types of tyre are cross-ply and radials, although cross-ply tyres are no longer commonplace on cars. Tyres are rated according to recommended speed as follows:
Q - for up to 100mph (usually winter tyres)
R - for up to 106mph
S - for up to 113mph
T - for up to 119mph
U - for up to 124mph
H - for up to 130mph
V - for up to 149mph
W - for up to 168mph
Y - for up to 186mph
ZR - for up to and above 149mph
Can I mix different sorts of tyre?
Except in the case of temporary use spare tyres, it is both illegal and dangerous to mix radial ply and cross ply tyres on the same axle, or to have radial ply tyres on the front axle and cross ply tyres on the rear axle. This applies to all two axle motor vehicles whether front or rear wheel drive. The type of tyre is indicated on the sidewall markings.
All tyres must be the same size, and we do recommend fitting both front tyres, or both rear tyres at the same time. (It is preferable to fit a full set at once.) However there is no legal bar to having different makes of tyre on your vehicle, so long as all they are of the same type.
What happens if my tyre pressure is too low?
Low tyre pressures (or overloading) will cause increased fuel consumption, more air pollution, shorter tyre life and greater risk of tyre failure.
What happens if my tyre pressure is too high?
High tyre pressures may cause reduced comfort, less grip, greater risk of impact tyre damage and reduced stability in braking and cornering.
How should I check my tyre pressure?
It is recommended that you check your tyres every two weeks and only when the tyres are cold. Even a short journey will warm the tyres and raise the pressure. Accurate and reliable gauges are not expensive and will soon pay back their cost.
Recommended pressures may vary according to load or speed. Look in the vehicle handbook, or consult your garage or tyre dealer.
What are the penalties for driving with illegal tyres?
The penalties for offences related to the use of faulty tyres on vehicles are very severe.
In the case of any vehicle, except goods vehicles and vehicles adapted to carry more than eight passengers, for every offence there is a fine at level 4 of the standard scale with discretionary disqualification and compulsory driving licence endorsement with 3 penalty points.
Level 4 is currently £2500 and each faulty tyre is considered as a separate offence. Two faulty tyres equals £5000.
Tyre Efficiency Labelling