I'm going to be running 32x11.5 tires on 15x8 rims. What backspacing should I get on the rims?

 

that depends on how far you want them to stick out.
personally, for 8 inch rims, i like 3.75. they stick out a bit to help in off camber situations, and won't rub.

but if you want them to be more in line with your stock factory flares, go 4 inch. you should still be fine without rubbing.

 

my lift kit 4.5" recomended 15X8 with 4 inch backspacing with my 32" tires

 

Thanks guys