I take back what I said earlier about tire wear just being a way if life on SL500 w/ oversized wheels/tires. I have since looked at several SL's with the AMG Sports package on them and have not noticed any unusual tire wear. This combo is the same size that I have on mine (275/40/18's and 245/30/18's or something like that).

I now believe that either my offsets are incorrect or I have an alignment (toe-in) problem.