Originally Posted by Bielzebub
Yes, what's this with backspacing? I am running 29s right now and don't want to muck up my '99 when I move up to 31s.
more backspacing = mounting face of wheel is further out, and the tire is subsequently further inboard....giving a narrower stance.
less backspacing = mounting face of wheel is inset into the wheel more, and the tire is subsequently further outboard...giving a wider stance.
when talking about stock 29-30x9.5 tires, 5.5" backspacing is what the factory gives you. this works great.
as the tires get taller & wider, you start rubbing on the control arms when you turn, or on the spring bucket in the rear. The easy solution is to reduce the backspacing.
You do this either with wheel spacers, or wheels with less backspacing.
But now, when you decrease backspacing, you're pushing the tires further out. While this fixes the clearance problems described, it introduces new ones. Now, when you flex, the tire no longer tucks inside the fender, it now wants to rub on the steel lip or flare of the fender.
When talking about running 31x10.50R15's on stock suspension, there is a sweet spot of backspacing...where you have no rubbing, but the tires still fit inside the fender flare. Generally speaking, a 15x8 wheel with 5-5.25" backspacing will work perfectly. Most stock wheels are 15x8 or 15x7 with 5.5" backspacing, but you can make these work by adjusting the steering stops with washers so you don't rub the control arms when turning.