backspacing for 33s

[Grinder]

I need some advice as to what backspacing I need to run
33s on my explorer. I will be installing a 6" skyjacker
setup soon and want to run 33x12.5 mud terrains on 15x8
wheels. I want the tire to stick out as little as
possible, but avoid rubbing. I'm confused though as I've
been told everywhere from 3" to 3.5".
Any opinions or pictures would be great.
THANKS

 

[FROADER]

I have 3.5 with 12.50 and there is no rubbing. They don't stick out much either. This is a picture of a 4" lift with 33's with the 15x8 with 3.5" backspacing.

 

[FROADER]

 

[tiessen]

You can just run neutral offset 8" rims with no or minimal rubbing...