I'm toying with the idea of going to 18" wheels on my GN. The wheel comes in a 18 X 8 with 4.5" backspace I know I can use on the front, but would like to go to the 9.5 wheel on the rear, using 275 or 285 40s, but the backspace is on the larger model is 5.3". I think that's too much. Anyone know for sure? If I use a 7/16" wheel spacer, that would knock it down to under 5". Anyone know if that would that give me enough room?