Different tire sizes and Quattro, should I be worried?
 

To make a long story short: hit a pothole with aftermarket 18's and bent/cracked front passenger wheel, model of wheel no longer made in the 5x112 bolt pattern, will have to replace all four wheels. I just bought a stock 15" wheel to use until I decide what to do about the rest of the wheels. The problem is the stock wheel and tire I bought have a slightly smaller diameter than the other wheels I'm running. After doing some research it sounds like the consensus is the torsen center diff and the open diffs at each end will be able to handle the difference in wheel speeds since it is all mechanical. The question I have: will this wear out the differentials or cause other damage if used for a prolonged period of time? I'm not sure when I will be able to get all new wheels and will have to live with what I have for a while. I am also planning on moving soon and will have to make 300 mile drive to my new place of residence. Any input will be GREATLY appreciated.

Yeah that doesn't sound like a good idea. A bit of around town driving might be ok but 300 highway miles on 3 18's and a 15 is no good. I'd try to at least find a spare 18 to get them a little closer. Maybe try ebay?

Just did some quick calculations to find the diameter difference. The stock 15" wheel has a 205/60 tire which gives it a 24.68" diameter and the 18's have 225/40 tires which is a 25.97" diameter which ends up being a 1.29" difference in diameter.

Get the right size wheel, before embarking on a 300-mile trip.

yea i think you can only go into <5/32 inch difference with the quattro. over an inch is just asking to empty your bank account.

Thanks for the input! I'll get some new wheels and tires thrown onto my baby a.s.a.p.