Backspacing is the distance from a wheel’s mounting flange to the farthest point inboard on the wheel. Some manufacturers measure from the mounting flange to the bead and not to the little lip around the circumference of the rim, but Weld uses the latter method. Also, make sure to measure from the exact point where the wheel will contact the car, not from any depression that may be around the lug nuts. Deeper backspacing moves the wheel and tire inboard on the car; shallower moves them outboard.