Originally Posted by clarkstoncracker
can you find the proper info so I can correct that?
No. That's 3rd-year Michigan State arithmetic.
To calculate offset, subtract half of your rim width from the backspacing.
You already know the backspacing, so the offset is meaningless at this point. If you are confident that the backspacing values you posted are correct (more likely), just delete the offset numbers from the post. Backspacing gives you the answer you need anyway. The stupid thing about offset is that you need to measure backspacing to calculate it. It also confuses people since it introduces both positive & negative values into what you are trying to figure out, where backspacing is always a positive (or absolute) number.
I suppose its technically possible to have a negative backspacing value, but I can't recall ever seeing an application on a passenger vehicle where the WMS stuck out past the inside edge of the wheel.