Tyre Tread Depth - The Law

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Remember you need good tyres to drive safely. They are your only contact with the road and affect the steering, braking and acceleration of your vehicle.

Department for Transport Tyre Safety: Information and Legal Requirements

You need good tyres to drive safely. They are your only contact with the road and affect the steering, braking and acceleration of your vehicle. This Page explains the legal requirements and the precautions you should take to ensure that the tyres on your vehicle are safe.

What your tyres do

Your tyres, each with a contact patch on the road of about the size of a large footprint, have to provide ALL of the grip for:

• Steering
• Braking
• Acceleration

They also improve comfort whilst carrying the weight of the vehicle. If you look after them they will work more reliably and last longer. Neglecting them could be expensive in the long run and could even cost you your life. Every new car type tyre must meet European standards for load/speed performance and be marked on the sidewall with E or e.

Tread depth

The legal minimum tread depth of the main grooves of car and similar tyres in the United Kingdom and the European Community is 1.6mm. This applies across the central three quarters of the breadth of tread and round the entire outer circumference 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. Tyre tread pattern is designed to give good grip in wet conditions. Generally speaking available grip reduces as the tyre wears or as the road surface water depth increases - you should reduce speed in such conditions.

The 1.6mm minimum limit applies to:

• Cars and passenger vehicles with up to 8 seated passengers-not including

the driver

• Motor vehicles & light trailers (including caravans) up to 3500Kg gross

vehicle weight

Retreaded Tyres

The only part of a tyre to wear away in normal use is the tread and it makes both economic and ecological sense to give a new lease of life to an otherwise good tyre by what is now generally known as retreading. All retread 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). The British Standard requires strict examination and inspection of retreaded tyres at all stages and they must meet the same load/speed performance standards as new tyres. The tyre debris, often seen at the roadside, does not necessarily come from retreaded tyres and is mainly the result of under inflation or overloading. Retreaded tyres are used extensively on aircraft and in motoring competition.

Part-worn tyres

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. Regulations require a part-worn tyre to be marked "PART-WORN" adjacent to the E e or BS mark, to indicate that it has been properly examined internally and externally before being offered for sale. Some faults only show up if the tyre has been inflated. Tread depth must be at least 2mm across the whole breadth of tread.

Mixing of tyres

Except in the case of temporary use spare tyres, it is illegal in the United kingdom, and it is certainly 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. In the case of radial tyres the word ‘radial’ is written on the sidewall.

Tyre pressures

Correct tyre pressures are vital for safe handling and optimum braking, grip and tyre life.

• Low tyre pressures or overloading will cause increased fuel consumption,

more air pollution, shorter tyre life and greater risk of tyre failure.

• High tyre pressures may cause reduced comfort, less grip, greater risk of

impact tyre damage and reduced stability in braking and cornering.

Incorrect tyre pressure will in addition to less grip also cause uneven tread wear:

• Too high pressure will cause more tread wear in the middle, indicating less grip in the outer parts of the tyre
• Too low pressure will cause more tread wear on the outer parts of the tyre, indicating less grip in the middle

Either of these are unsafe, as they do not take maximum advantage of the part of the tyre that's touching the road surface.

Pressures should be checked at least every two weeks and only when the tyres are cold. Even a short trip to the local garage will warm up the tyre 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.

Penalties

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.

OFFENCES CAN RELATE TO:

Tread depth: a tyre worn below the legal minimum.

Mixing: an incorrect mixture of radial and cross ply tyres.

Inflation: a tyre not inflated to make it suitable for the purpose to which the motor vehicle or trailer is being put.

Cuts: certain long and deep cuts as specified in regulations. Lumps, bulges or tears: caused by separation or partial failure of the tyre structure. Exposed ply or cord

Unsuitability: regarding the use to which the motor vehicle or trailer is being put or to the types of tyres fitted to its other wheels.