I'm eyeballing a set of 15x8 all around... what backspacing should I be looking for? I'm thinking a 4" or 4.5"

Anyone else running 15x8? input?

 

4.5" is a zero offset, 4" is a negative offset. Those will stick out of the fenders, in other words, it won't fit. You need more like a 5.5" backspace to have a hope of fitting a decent tire in front.

 

Thanks! found them in a 5" backspace... should work, if not I can space them.

 

No, it works the opposite way to that. Spacers reduce backspace, not increase it. I don't think 5" backspace will work with tires wide enough for the rims. I'd say 5.5" backspace as a minimum if you want them for performance purposes. You might get away with 5" and 205 wide tires, maybe needing rolled fenders.