With just a 2.5" spring lift and everything else stock, you can run 31's w/out rubbing max. You'll need to trim the fenders a bit, or get new roomier flares, install a 1"BL, or install a 1" shackle lift, rims with proper backspacing, to clear 33's w/out rubbing. It really depends on what you want and where you want to wind up in the end. You could even get tube fenders and that's it, I don't have a spring lift and only a 1"BL, but my tube-fenders give me enough room for 33's. What else do you have besides the spring lift though?