[Hope Springs Hauler]

I'll try this. Let me know if it sounds way off base.

Backspacing is the measurement from the inside of the rim to the interior WMS.

You are asking about the measurement from WMS to the outer part of the rim.

So, take the wheel width and subtract the backspace and that should give you the measurement that you are looking for.

If we work this backward, an 8 inch wheel width - 5.25 inch desired outer measurement yields 2.75-inch backspace. You could probably get by with a fuzz more backspacing since you are welding on a beadlock kit.