I know a guy that has Enkei V1's 18x8.5 with 235/40-18 tires on his Eclipse right now. He had to roll the rear fenders but has no problem with rubbing. Plus it's lowered with ground control coilovers. So whoever thinks it can't be done....it can!

Anyway, here is a easy formula for calculating overall tire diameter:
Here is an example of a 235/45-17 (sectoin width(235) x 0.aspect ratio(0.45))x 2 divided by 25.4(this number will never change) + wheel diameter(17) = Overall Diameter.

235 x .45= 105.75 105.75 x 2= 211.5 211.5/25.4= 8.32
8.32 + 17= 25.32

05 STi