[lnfletcher]

The Backspacing is figured from the mounting face to the inner rim.
If you lay the bare rim facing up on a flat surface, then measure from the mounting face to the flat surface, this is your backspace. Whether it is a 10" rim or a 8" rim, the backspace would be the same for a particular vehicle not considering the tire buldge. By adding backspace, you are pushing the wheel outward. The wider the rim and more backspace moves the outer tire out by both amounts.
This would mean that you would have 1 3/4" more space behind the tire to the inside than me and 3/4" more than Wayne.
Spacers would make it even more!
Clear as mud?