1. What do the size markings on the sidewall of a truck tyre mean?
2. What is the minimum legal tread depth for a truck tyre in the UK?
3. Can Truck Tyres be repaired?
4. What is Regrooving?
5. What does the modern construction of a truck tyre look like?
6. What materials are used in a truck tyre?
7. How can I determine the age of a tyre?
8. What does the Ply Rating or PR mean on a truck tyre?
9. What is the effect of incorrect inflation pressures on tyres?
10. What points should be considered when choosing replacement truck tyres?

1) What do the size markings on the sidewall of a truck tyre mean?

The tyre size markings indicate the dimensions, type of structure and the load and speed capabilities of a tyre as follows: -

2) What is the minimum legal tread depth for a truck tyre in the UK?

The legal minimum tread depth in the UK for Heavy Goods Vehicles (above 3500kgs) is shown below:

The tyre must have a minimum pattern depth of 1.0mm throughout a continuous band measuring at least three quarters of the breadth of the tread and round the entire outer circumference of the tyre.

OR

If the grooves of the original tread pattern did not extend beyond three quarters of the breadth of tne tread, any groove which showed in the original tread pattern must have a depth of at least 1.0mm.

NOTE: Exclusions from the definition of tread pattern are: - tie bars, tread wear indicators, sipes, any feature designed to wear out substantially before the main grooves

3) Can Truck Tyres be repaired?

Yes, but the repair should be carried out in accordance with the current British Standard AU 159. An illustration of the current minor repair limit for commercial vehicle tyres is shown below: -

4) What is Regrooving?

A regrooved tyre means a tyre, either new or remoulded, on which a tread pattern has been produced by cutting into the tread in accordance with the tyre manufacturer's recut tread pattern. Such tyres will have the required amount of under-tread rubber for this purpose and will be marked as REGROOVABLE. This is illustrated below: -

5) What does the modern construction of a truck tyre look like?

A radial tyre is constructed as shown below.The belt assembly comprises several layers of steel belt plies arranged in diagonally opposing directions at a specified angle. This belt assembly provides support and stability to the tread area so that forces in all three principal planes can be transmitted efficiently.

6) What materials are used in a truck tyre?

A tyre comprises different components, all of which contain elements in varying compositions.

These elements vary with the size and type of tyre.

Listed below are the elements used for the 315/80R22.5 tyre. This particular tyre weighs approximately 62 kg.

7) How can I determine the age of a tyre?

This can be found by looking for the DOT code on one sidewall of the tyre. The DOT code comprises a sequence of letters and numbers and can be interpreted as follows: -

8) What does the Ply Rating or PR mean on a truck tyre?

The ply rating, or PR for short, is an internationally used standard for the structural strength of the tyre sub-structure. The term stems from the time when cotton was still used for the fabric sub-structure. In those days PR actually referred to the number of plies. When materials with greater strength were introduced, the same structural durability was achieved with fewer plies.

PR therefore now refers to a load capacity category and is being increasingly replaced by the Load Index.

9) What is the effect of incorrect inflation pressures on tyres?

One of the most important causes of excessive tyre wear and damage is incorrect tyre pressure.

Service manuals produced by the vehicle manufacturers and technical documentation from the tyre manufacturers provide information about correct tyre pressure. These values apply only to the tyre when cold, as the inner pressure of the tyre increases when it heats up in operation.

Tyre pressure should be checked every 2 weeks. At the latest every 4, on the cold tyre. Spare tyres must also be checked.

Under inflation leads to: -

• Increased flexing, which makes the tyre overheat and may cause tyre failure;
• Increased wear means shorter service life and is illustrated in the graph below:

• Higher rolling resistance and subsequently increase fuel consumption as illustrated below: -

• Irregular wear e.g.-

10)   What points should be considered when choosing replacing truck tyres?

Replacement tyres must be suitable for the type of vehicle and the applications in which they are to be used. These applications may vary (type of service, route, load, speed) but tyre manufacturers offer a comprehensive range of tyre sizes, constructions and tread patterns and are the only bodies competent to advise the user on tyre selection.

This advice is supported by extensive facilities, both equipment and personnel, for carrying-out research and development over the full range of service conditions. In special cases, a change of tyre and/ or wheels may be necessary.