[strictlypersonl]

I pretty much gave up giving wheel makers the actual offsets (which is the most accurate way to define the wheel). Most of them only want the backspacing. You can figure the offset by adding about .8" (an average edge width x 2) to the nominal width, then dividing by 2. The difference between that number and the backspacing is the offset.

Just to make things even more interesting, not all companies define offset in the same direction, so it's best to send them a well-defined drawing.