I have one bad tire and I a wondering whether I can just replace that one and continue to run the other 3 (they have about 1/2 of tread life left). I had a Subaru a while back and once, after having a blowout, was told by the tire center that, different tire diameters (i.e. one brand new tire w/ three older tires) could cause damage to the AWD system and/or transmission. I believe the AWD systems used on volvos are different from Subarus, but I am wondering whether that is still a concern. (The tire center, a local operation that I believe I can trust, has said that they "ate" one system to the tune of $972 and don't want to risk another.)