7.5" might be pushing the limits. With the proper offset you might be able to get away with it. I have a 7" width and a 42mm offset and it was pretty close to sticking out too far. 215 was my cross section tire and it fit fine, you might be able to get away with 225.
Well I think it all depends on offsets really...if you get 18x8 rims you will most definitely will have to get a high offset like +45 or even higher...I had 18x7.5 with +43 rims on my P11 with 225/40ZR18 tires...fit perfect...and cleared the suspension by a hair..