what offsets on your 8" wheels? that will determine how big u can go on tire size obviously.

w/o fender modification u can run pretty big tires, just takes the right offsets. for a 16x8 with a ~+30mm (using R32 wheels as example), u can run 245 on an 8, 245/45-16 would be a nice wide patch, but 225/50-16 or 235/50 is a good one too, it just depends what you wanna pay for and what u think looks and feels right. anything under 225 on an 8" wheel is gonna be a little stretched, u can do 255 on 8, 265 would get bulgy. (255 might bulge a little)