[strictlypersonl]

Simple calculation:

Offset=backspacing - (wheel width/2)

(That's bead to bead width, not rim edge to rim edge).

Be careful when comparing offset numbers. Some (like me...) define positive offset as moving the wheel toward the outside. Others (like the chart) define it to the other direction. The change probably comes from the transition from rear drive to front drive and/or a reduction of the king pin offset in most cars.