your best bet then is to go with a 18"/20" combo 5" backspacing 9.5 " in the rear and 8" 4.5 Backspacing in the front, as long as you stay with 50 series or smaller (ie. 45 40's) you should be fine, but you can not make a full tilt turn, especially at high speed, it will drag on the fender well. I would make sure the suspension is tuned correctly. 5-7 with 20"s all the way around is impossible unless air bagged...
