COMMERCIAL VEHICLE TYRE DATA - legal requirements
Commercial vehicle tyres and the law
Staying within the law as regards commercial vehicle tyre regulations can be somewhat complicated. If your tyres are managed by a specialist tyre contractor, then you should expect that contractor to know the law and keep your vehicle tyres legal.
MIXING TYPES OF COMMERCIAL VEHICLE TYRE
The regulations are strict when is comes to mixing the two types of tyres. This is because of their different behaviours and the effect that they could have on the handling of a truck.
- It is illegal to have tyres of different types fitted to the same axle.
- In the case of a truck with two axles, cross-ply tyres must not be fitted to the rear axle if radial-ply tyres are fitted to the front, unless the rear axle is fitted with wide tyres having a tread contact width per tyre greater than 300mm or having twinned-tyre wheel assemblies.
- It is illegal to mix types of tyre on steerable axles.
- It is also illegal to fit tyres of different type on two or more driven axles.
As far as the law is concerned any two wheels of a truck or trailer are regarded as one wheel if the distance between the centres of their areas of contact with road is less than 460mm. For more information, see 'Construction and Use Regulations" 26 and 27.
These rules apply irrespective of whether the tyres have standard types of tread patterns, off-road patterns or are 'mud and snow' types.
TYRE CONDITION AND THE LAW
Apart from the rules applying to the mixing of cross-ply and radial-ply tyres, there are many others relating to the condition and use of tyres on trucks.
- It is illegal to run a vehicle with a tyre at the wrong pressure
- It is illegal to run a tyre that has a cut longer than 25mm (or 10 per cent of the section of the tyre, whichever is greater) and deep enough to reach the ply or cords.
- It is illegal to use a tyre with a lump, bulge or tear - or with any of the cords exposed.
DEPTH OF COMMERCIAL TYRE GROOVES - LEGAL REQUIREMENTS
- The grooves must have a depth of at least 1mm around the whole circumference and across three-quarters of the breadth of the tread.
- If the original tread pattern was only across three-quarters of the tread, all grooves must be at least 1mm deep.