Really depends on the truck, I have a 4" lift with 33's. I could probably stick 35's under there but it would be tight...probably too tight. I am intending on going up in tire size, but I'm planning a shackle flip to gain a couple of inches. For planning purposes, I would say a least 5 or 6...and I'd lean towards 6. But then you might have to modify your brake lines and possibly the driveshafts.