When I had 31x10.5" tires I ran them on the stock aluminum cast 15x7" rims. No lift at all and no modifications necessary. Performance was reasonable (I have a 2.6). Now I run 33x12.5" tires on 15x8" rims. I put them on right after I did a 2" body lift. The bumper end-caps had to get trimmed (I just removed mine altogether but shortly after I got a Don bumper) and the splash shields at the front of the front wheel-wells had to be bent forward slightly. Recently I put in a 2" suspension lift and I have GOBS of room (enough to squeeze in 39s!) so when I wear out my 33s I may move up to 35s.