quote:Excellent point. My aftermarket rims don't have that extra lip. So instead of an extra 1/2 on each side like the drawing, mine have approximately 1/4 extra on each side. So my 9 inch rims measure 9.5 inches from the outside to the outside portion of the rim. They measure 9 inches where the tire seats.
My rear 12 inch rims measure 12.5 from the outside lip to the outside lip.
This is exactly why most high-end wheel manufacturers nearly always refer to offset as opposed to backspacing. With offset, the thickness of the outer "lip" doesn't effect the measurement. You would typically only have a half-inch thick outer lip with a cast alloy wheel.