what backspacing would create less rub when running 10" rallys?

[weider1717]

Not sure what my original 8" rally back spacking / offset is?

But if I lift my k10 2.5" and run 33x12.50's on a 10" rallys (they don't make 9")
what off set would HELP with rubbing issues due to the wheels being wider than the 8" rallys?

I like the beefier look so I thought if you counter some of the extra width with more / less offset maybe that would help some?

thanks guys