On a 2004 VW R32 (which uses a Haldex AWD system), I have one damaged summer tire. All the tires have at least half of their usable tread depth left. At $200 ea, I'd like to replace only a pair of tires, which I'd mount on the front of the vehicle where the wear occurs more quickly.
A TireRack salesman said that some AWD vehicles have a tolerance of 2-3/32" tread difference between axles to avoid damage to the transfer case (his term, i'd call the component in question a center differential), and that I should check with VW before buying the new tires.
VW customer care gave the answer that as long as the two tires new tires are either both on the front or both on the rear, that it's OK. In other words, there's no tolerance limit. I find this somewhat hard to believe. A VW dealer I called gave the off-hand answer of 6/32".
Would having tires of different size on the front and rear axles put extra stress on the center differential of an all wheel drive car?