Tyre Rotation and Matching

Rotation

It is better, according to experience, to leave twinned tyres in their relative positions to yield better tread life under most conditions. They should be rotated only if irregular wear such as heel and toe sets in. Inners and outers must stay in those positions. If an inner from one side of a vehicle is moved to an outer position on the opposite side, it will not change its direction of rotation. See illustration below for directions on how to carry out this rotation.

It happens that one twin will wear more quickly than its mate and very often it is the outer tyre which wears more rapidly. This process will only be accelerated if the position of twins is swopped, as they tend to develop the wear pattern suited to them.

Recommended method of rotation where heel and toe or irregular wear develops.

Matching

After pressure, top priority goes to the correct matching of dual tyres to obtain maximum service.

Because different brands of tyres have different diameters, especially after retread, it must never be assumed that unworn tyres are equally matched.

Application of the principles that follow will eliminate many cases of irregular wear, overheating, blow outs and rapid wear.
Simplify the task of selecting and checking by using a "matching stick".

1. Single axle duals

The ideal is to match duals exactly but if this is not possible, a maximum difference of 6mm up to 825 section tyres and 12mm for 825 section and above is allowed.

A pair of duals should not differ by more than 25mm from the other pair across the axle, or the differential may overheat.
The smaller dual should be fitted on the inside and pressure should be exactly the same.

2. Dual axle bogeys

The same rules apply here as to the above. Avoid fitting the larger pair of duals to one axle with the smaller on the other.

llustrated below are the methods to apply -(A) represents the larger pair and (B) the smaller pair. The revolutions on the front and rear axles will thus be roughly equal.