evening all, just wondering what the allowable limits are for the differences in tyre wear. my car is an 09 sti ppp. ive been told that 1mm difference between front and back is the maximum, or the diffs can play up. is this true?

 

Nah I wouldn't believe it has that small a tolerance personally.

 

thanks for the reply, it mentions nothing in the handbook that comes with the new car about this so i was a bit dubious about believing it!

 

Your best bet is to ask a Scoob dealer, or one of the respected tuners on here.

 

Taken from wrx tuners FAQ

Q: They tell me I can't replace just one tire? What's the deal?

AWD cars are very very sensitive to differences in tire height. The stock tires are all around 25" but even a small difference can be a major problem for your differential given enough miles. Subaru will refuse to mount a tire on your car that's not within 1/4" circumference AND they must be identical. If you intend to replace a tire with a new one, the other tires should all be within 1.3/32 of an inch of new tread depth.

Ok, lets be fair here that many guys want to sell you more than one tire to make more money. However, this is still a valid concern. Demand they give you the measuring device (or better yet own one yourself, they're cheap) and simply measure the tread depth between the tires on there and the new one. If they're within 1/32, they shouldn't give you any gripe about replacing just that one. If they're not, you should listen to them and buy a new set.

Tire rack and some other vendors will shave a new tire down for you (for a price). If your tires are about 4/32" worn, you can pay a few bucks and get a new tire shaved down that far to match. Not always an option if they don't have your tire in stock anymore and may not be cost effective destroying a new tire just to match the old ones.

Q: Can I run two different tires on my car?

Basically no. For emergencies, it'll work fine (as long as it's ~25"). The spare Subaru gives you is way small so clearly the differential can handle it for a few miles. For longterm use, tires wear differently so it's not a good thing to do. Your car's tires should be within 1.3/32 of an inch of each other! That's not very much and different tires with the same size can be more different that this. One type of tire is always a big deal with cars but with AWD cars, it's a must!

 

(1.3/32) inch = 1.031875 millimetres

Just noticed that's going on about new tyres, but should be the same for rotation as well to keep them with in 1mm