The easiest way to measure backspace is to put the wheel face down on the ground. Lay a straight edge across the rim of the wheel. Using a ruler or tape measure, determine the distance from the straight edge to the face of the flange mounting pad. This measurement is the wheel backspace. On this American Racing rim, the backspacing is 331/44 inches. The offset is the distance from the face of the mounting flange to the true centerline of the wheel.