Backspacing on 15x8 on a 69 C10

[ShamrockCustoms]

With the wheels off, take a good straight edge or level. place this at the wheel mounting spot on the rotor. From the top of that straight edge, use a measuring tape to see what your distance from the straight edge is to the fenderwell. That will be your max backspace clearance. (Note: this does not take into effect the turning radius of the OD of your tire!, you must compensate for this or you will rub the tire on fenderwell.)

Then , you can also measure from the straight edge to the lip of the fender to get the outside clearance measurement. The total of both would be the max width wheel you could run, but again this does not take into account the turning radius. You must compensate for this. Make sure you have clearance! Good luck!