Thread: Tyre rotation - unused spare

Some measurements, for the sake of curiosity...

Tread depth on new (spare) tyre: 13mm
Tread depth, worn tyres: 8mm

I calculate difference in tyre diameter new vs. worn equates to 5 extra revolutions per road kilometer (397 vs 402).

Hardly a lot of extra work for the diff i woulda thought? (compared to going round a corner)

I got this from here some time ago!


5 tyre rotation - Spare to Rear Left, Rear Left to Front Left, Front Left to Rear Right, Rear Right to Front Right, Front Right to Spare.
6 tyre rotation - Spares to same side, Fronts crossover to Rears, Rears to same side Spare. DON'T crossover or change sides if the tyres are directional.

Originally Posted by Samblers

Some measurements, for the sake of curiosity...

Tread depth on new (spare) tyre: 13mm
Tread depth, worn tyres: 8mm

I calculate difference in tyre diameter new vs. worn equates to 5 extra revolutions per road kilometer (397 vs 402).
Hardly a lot of extra work for the diff i woulda thought? (compared to going round a corner)

good work, I like crunched numbers, especially with honey.

It is then the equivalent of turning one very big corner for the next 10K kms.

It may be more salient to consider the traction issue when braking in the equation too. Uneven braking, especially in the wet, in a car that likes to roll over but is especially unsuited to keeping you alive while doing it.

Also, a new tyre is stiffer than an old tyre at any given pressure. so at 45psi the diameter is not just the difference in the treads but also in the compression difference.

Still perhaps the diff issue is a non-issue overall and it has always been the braking/steering etc of concern to those who make the 'rules'?

Time to put the theory into practice ...

And our roads slope down to the left, thus putting more pressure on the left wheel. And you turn right more than left which would also put more pressure into the diffs/centre diff. In my experience, rotating in a new tyre has little effect on any of this. Like someone else said, it's really like turning a really shallow corner for a while. If you're concerned, swap it around every wheel every few thousand kms to get the wear even .

And in my experience, road camber and condition would have more effect than grip depth (within limits of course ) on emergency braking and steering.

just rotate it in and dont worry about all the perfect world theories.......

it will not harm anything and you will get less tyre wear.......


they are all the same size....type....brand....etc...you wont have any problems....

the hand book wouldnt tell you to run different pressures if the diffs couldnt compensate for it......

are you shoes worn identically left and right......?
can you still walk in a straight line......?

I've always rotated the tyres every 10,000km with tyres staying on the same side of the vehicle - but I've just learned that's old hat! Here's what Bridgestone has to say about it:

Tyre rotation

I can't see anything in my L/R owners manual about rotating tyres.

Also - the placard on the fuse box cover says that 'a single axle roller rig may be used for speeds up to 5km/h..' I've always thought this means that the centre diff is happy with a difference in speed of up to 5km/h between the front & rear axles so haven't worried too much about introducing new tyres into the rotation.