I agree with Matt. I've never run 315 but Punisher from here has, and I'm pretty sure he had to remove the quads and MAYBE roll the fenders, not sure tho. But IMHO, a 295 is perfect and a 305 is MORE than enough for our cars, anything wider looks too wide, EXCEPT if you have a wide body kit like Punisher(Paul).
FWIW, I have a buddy who had 295/30/18s Toyos on his saleen wheels and that thing looked awesome.