Im trying to figure this measurement. I have these 15x10 that i took off my jeep to test fitment....




As you can see in this picture it has a 3.75 back space...




In this picture you can see it sticks out 1.375" out side of the fenders





So if minus the 1.375" extension passed the fender and add it to the 3.75 back space ill have a 15x10 wheel with a 5.125 back space right?

 

Are you sure your brakes are gonna fit behind a set of 15s?

 

yes. the wheels i have on in the picture are 15x10 with a 3.75 back space. I most mention this is for drag racing purpose

 

that wheel doesn’t hardly have any backspace though and clearance could change depending on the wheel being used

unless you want it to be right at the fender flare lip with max track width, then I’d also check the inboard clearance and determine what offset would center the wheel between the two extremes and how much clearance that provides, which should then be the same dimension on both sides. You can then use that and comparing the max width possible against the mounted tire sidewall width along with some safety clearance to then calculate the offset needed to place the tire where you want it.

If I’m not mistaken, approx. 7.5” is considered about the max BS you can use before getting into inboard clearance issues. That assumes the std. 1/2” wheel bead-seat to outer lip dimension. It could also depend on how much wider the tire sidewall is than the wheel lip edge.

but then based on your measurement and that potential max BS dimension, it works out to about 12.375” total clearance between the inboard and outboard extremes if I calculated it right.
.