I checked clearances before considering changing wheels, and I have enough clearance to run wheels with up to 5 3/4" of backspacing, and the limiting factor there is clearance between the wheel and the tie rod end, not the tire and the frame, or control arms. The frame is narrower at the front, and then widens out right about where the front of the body is at. I'm running 37s, and at full steering lock, they are still in front of where the frame widens out. 40s would present a problem, because they would rub where the frame is wider. With my axle width I would have the same overall width using wheels with 6" of backspacing as a Jeep with stock axles and wheels with 4 1/2" of backspacing. Or, stated differently, if I can find wheels with 5" backspacing, which would be ideal, it would be the same as a stock axle Jeep running wheels with 3 1/2" of backspacing, which is plenty of room for 37s.