Alternate tire size on rear wheels?
You should always try to keep the overall diameter between the front and rear as close as possible:
stock:
245/40/18 = 25.7"
265/35/18 = 25.4"
I dont think 255 tires can fit the front. Very few companies make 255/40/18 tires, I think only Michelin Pilot Sport A/S and Continental make them, are you sure about those two tires? Have you heard the "pulling to the right story"?
IMO, you should keep your car as is now.If you want to put all-season tires for the snow, I would say.... forget about driving it on the snow. Otherwise, you car is best equipped with Ultra High Performance tires, its too powerful, you need A LOT of grip.
Anyway, you may want to look at the Goodyear GSD, or call Luke at the Tirerack.




