Damaged on tire and needs replacement. all the tires have about 15-18K on them. The tire guy says I need to replace all four tires, as even a slight change in size from a worn tire with 1/2 the tread and a new tire will cause problems with traction control, etc. I know that X drive needs all four tires the same size, but will this really make a difference?

 

First of all, get the exact measurement of the tread remaining from them. My gut instinct is it's BS you have to replace all 4!

I ran into the same problem, two tires blew, and the other 2 were good (at first though I thought it was just one RFT that had a bulge in it). They have some tech articles on Tire Rack about this, so read up there a bit. The tires had about 14,000 miles on them, and still had 7/32 of tread left, which is pretty good. New, they have 10/32 of tread. You're allowed to go down to 2/32, so that's 8/32 of usable tread (usable tread will be referred to in some articles).

Some mfr's give guidelines as to how far apart a tire can be from the other on the same axle. If needed, Tire Rack I read can even shave a new tire for you to match the other on that axle! From what I've read, it's more important to have the tires on an axle match each other, than front and rear axles too. So if you have to replace a pair, which you can get away with, they say it's best to put the new pair on the rear.

Read these too:

http://www.e90post.com/forums/showthread.php?t=541246

http://www.e90post.com/forums/showthread.php?t=538267