[mr0077]

Jim, I think to get at the flange-to-flange dimension, the wheel offset is what you want; you add twice the wheel offset to the track to get this dimension.

Backspacing is the distance from the inside lip of the wheel to the mounting flange, and offset is the numerical distance (plus or minus) from the wheel centerline to the mounting flange, with a positive offset placing the flange closer to the outside of the wheel. If you had a -2" offset on the rear wheels and the rear track was 52.5", the flange dimension would be 52.5" + [2 x (-2")] = 52.5" - 4" = 48.5".