I run 295 x 35 x 18's on the rear of my Cayman on 10" wide wheels and use 10mm spacers from Ralph Boothe Design to keep it from rubbing on the inner fender well and parking brake cable due to the wheel offset not being ideal. Up front I still run the stock tire size albeit on a 8.5" wide wheel. The rear tires are within a fraction of a percent of the original rolling diameter from the factory. I just have more meat on the pavement.
