Sorry for beating a dead horse about tire size

Most cars I see with fat rear tires have the jacked-up stinkbug stance. If you want it to sit low you have to center the tire in the well, meaning you have to have the right backspace for the wheel width. For example, say your current 4.5" wide wheel is perfectly centered, and it has 3-inch backspacing. If you go to an 8.5 inch wheel, you want it to fit so that it extends 2 inches further to the outside and two inches further inside, so add 2 inches to the backspacing — you need 5-inch backspace. Note that this is a hypothetical example — do not refer to these specific numbers. It may also be true that 1/4 to 1/2-inch either way doesn't matter, depending on your tire width.