That's only 25% worn, the rears come molded with 8/32" of tread from the factory.
8-10k miles out of a set of rears is not uncommon. I got 8k out of my first set and looking like about 15k out of my second set.
Static negative camber, in my experience, has almost nothing to do with excessive tire wear by itself, especially if you do any amount of spirited driving, because what you may grind off the insides is evened out by the periods where you're leaning on the tires and grinding down the center and outside shoulder. Once you start combining some negative camber with some toe-in like BMW does in the rear, you start to see more wear, and in the case of the E9x M3 it is fairly even. On my E46 it ate inside edges with the factory alignment which had even more toe-in. The idea that alignment can't affect tire wear unless the wear is uneven is just plain wrong. One easy way to get better wear out of rear tires since time immemorial has been to set the rear toe at zero. Bear in mind that on a car which is delivered with significant toe-in like the M3 this can have a big impact on cornering attitude and it's not for people who can't catch a slide without the computer.
Last edited by Richbot; 11-09-2011 at 08:04 PM.