Ill be buying a pair of MT 15 by 13.5 ET streets. I know to mount them on 15 by 10's but what back spacing should I use? I heard of using 7.5 inches but I cant find that combo anywhere. Can I Use a smaller back spacing?

 

I would think 13.5 wide is too large for a 10" wheel, and may be too big for the wheelwell. How tall is the tire? > 28"? Do some searching on what the max tire size is that people are using. Probably have better luck in the Drag Racing forum.

I have 26 x 10.5 x 15 on 15 x 10 Pro Stars w/ 7.5" backspacing. The tire bulges a bit in the sidewalls and rubs the bumpstop if i raise the body and let suspension hang. BTW - my bumpstops are about 1/3 gone for clearance on my 17 x 11 street wheels.

I would think 7.5 backspace would be the max you could go. If you go with less the wheel moves toward the outside edge of the car and you waste the space behind. Mike