[Trevor]

The rolling diameter of all the tyres must be the same. Surely it is obvious that if they are not, the wheels will be rotating at different speeds and the transmission driving all four wheels must continuously "slip" by way of compensation. This must cause wear and tear. There can be no argument in this respect and all written advice cautions accordingly.

There is a simple method of testing the tyres. On a flat even surface, mark all tyres at point of road contact and drive/roll the car forward in an exact straight line for as far as possible so as to rotate the wheels several times. The marked points should be as before, any change will show a variation in rolling diameter.

Tyre loading weight and tyre pressures obviously enter the picture and should be checked prior to the test. There could be minor variations of no real significance.

Edit P.S. This test could well be included in the "how too" section.