When changing tyres on a 4x4 vehicle there are a number of important things to consider. Two of the most important (and costly if ignored) are matching tread depths between new and used tyres if not replacing a full set and maintaining the correct rolling circumference if changing tyre sizes.

Matched tread depths are important as too large a difference can, on certain vehicles result in "wind-up" of the 4WD system differential causing serious damage. This will be dependent to some extent on the type of differential and 4wd system used on a particular vehicle.

For instance consider the following:

A vehicle fitted with 265/70R16 (Nissan Patrol size)

A new tyre will, according to the industry standard dimensions (ETRTO) have an overall diameter (O/D) of 792mm.

Average tread depth when new will be around 10mm.

A tyre with 5mm remaining tread depth will have an overall diameter of 782mm (original O/D - [2x5mm]).

To obtain the theoretical rolling circumference of the tyre you multiply the O/D by 3.05.

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Calculation:

New tyre rolling circumference
792 (original O/D) x 3.05 = 2416mm

Tyre with 5mm remaining tread depth
782 (O/D worn tyre) x 3.05 = 2385mm

Difference of 31mm

This means that the new tyre will have 31mm further to travel for every revolution of the wheel.

A tyre of this size will rotate approximately 413 times per km, therefore for every km driven the new tyre will travel an extra 12830mm or approx 13 metres!!!!

Tyre manufacturers and retailers have differing views about the maximum allowable difference in tread depths between new and worn tyres fitted to a vehicle but in general most recommend a difference of no more than 3 - 4 mm. All manufacturers will recommend fitting at least matched axle sets.

If in doubt consult the vehicle manufacturer before fitting new tyres.

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Tyre Conversions

As with the passenger tyre market the 4x4 market has also evolved into the high spec, high performance conversion area. Drivers of 4x4 vehicles now also expect the same conversion possibilities available to other motorists. It is nothing unusual to see vehicles originally fitted with say, a 16" tyre be upgraded to use 18", 19" or 20" tyres. It doesn't stop there though; 4x4 tyres are now available up to an incredible 26" rim size.

As with high performance car conversions, care must be taken to ensure that overall diameters and particularly load carrying capacities are taken into account when upgrading your 4x4's wheels and tyres. It is very difficult to produce a full list of conversion sizes for 4x4 vehicles given the number of different sizes available and all the other factors that need to be taken into account. Should you have a specific conversion in mind please do not hesitate to contact us where we will be able to advise suitability.