Tires: tire replacment on AWD car, audi a6 quatro, audi a6

Question
I have Audi A6 Quatro.  Tires are ~2 yr old, need to replace Right Rear Tire.  Costco telling me I have to buy 4 new tires.  Audi dealer says only need one new tire.  What is the right answer?  Is there a right answer?  What variables need to be considered?

Thanks!

Answer
Maureen,

The problem with AWD is that the tires have to be nearly the same rolling diameter or the center differential with bind up and fail.

So the safest thing to do is buy 4 tires.  If the Audi dealer is telling you to buy only 1, then have them buy it and install it.  If the center differential fails, then it is their fault and they will have to do the repairs for free.

However, I'll bet they won't do that when confronted with the possibility.  (It's also possible the person you talked to doesn't know this.)

Another possibility is to have someone "shave" a tire, to the same tread depth.  BTW, this only works on tires identical to what you have now.