I went from an 18" by 8.5" rim with 325/65/18's (35/13.50/18's) with slight rub on the inside fender well, to an 18x10" rim with the same tire and it rubbed bad when turned all the way. I ended up lifting the truck 6" after that as the lugs of my tires were rubbing on the 1/4 panel bad. I was afraid that if the suspension compressed I might rip my 1/4 panel off. Oh, I had a 2.5" leveling kit before the lift. My buddy has the same set up that I had but he is on stock 18" rims with Toyo MT's 35/12.50/18 and 2.5"level kit and he is ok. I think the wider rim might give you problems, plus you want 20"s.