I am running 18x9 saleen wheels in the mustang bolt pattern with +24mm offset. With 275/40/18's all the way around I have slight rubbing problems. Rolling the fenders a bit would alleviate the rubbing as it is only slight. I ran a 265 tire on the front at one point and had no rubbing up there. I think you would have no problems at all with a 255 width tire around 26.6in diameter.
Edited with more info!
Last edited by PearlBirdSC; 10-27-2009 at 01:52 PM.