When to replace both tyres?

[luckyhands]

What's the % difference between two tyres we can tolerate before replacing both?
Does Porsche have a recommendation?

Cheers

[gizlaroc]

What car?

Unless it is a Macan or Cayenne, not sure on the Panamera awd system, I would not be too fussed.

[luckyhands]

It’s for a boxster. My mate is picking one up and the dealer have replaced one tyres with a new one but he suspects that the other one is quite a bit more worn.

[Holgate86]

Depends who’s paying if it’s the OPC it won’t matter, if it’s the customer very little wear before they’ll want both tyres changing especially if it’s under warranty.....my OPC gave me grief over a professionally repaired tyre with 2000 miles on it and suggested I change both rear tyres.

[996Targa]

Our 986 handbook it states that the difference in tread depth in such circumstances must not exceed 30% on one axle.

This stipulation does not appear in our 991 handbook.

[Armitage.Shanks]

Holgate86 said:

.....my OPC gave me grief over a professionally repaired tyre with 2000 miles on it and suggested I change both rear tyres.

That's refreshing, whereas they sold me a car on Cup2s where one had been plugged!

[anonymous-user]

My understanding is the only question is whether the car is fitted with a limited slip differential. I would expect ABS and yaw control to cope without issues.

On a car with an "open" differential (non-LSD) I can't see that nuances of tyre diameter make any difference. Sure, the diff will be rotating a bit all the time but I don't see any reason for that to be a problem.

On a car with LSD the situation can be different because whenever the diff detects a material difference in wheel rotation speed it will be "working" a little and trying to limit that slip. Obviously the bigger the diameter difference the more work the diff will be doing. This can cause accelerated wear and/or overheating, depending on the type of LSD fitted.

On cars with 4WD - obviously not a Boxster/Cayman - then, depending on the 4WD system fitted, there may be two more differentials, one between the second pair of driven wheels and one between the front and rear axles. On some 4WD vehicles it's recommended that if you change one tyre you should change them all!