Do we have any offset calculating experts on here? I have been bending my brain on and off for the last week trying to figure out what offset I need for my rear wheels.

Currently I have 18x8 wheels, with I believe a +40 offset, and 1.5 inch spacers (adapters) to account for the widebody kit.

I would like to move to an 18x9.5 or 18x10 and eliminate the spacers. If considering a 9.5" wheel, logic would say that the width would be perfect (current 8" wheel + 1.5" spacer). The only real question left is the backspacing...

By the calculations my 8" wheel should have 5.5" backspacing (and does fit without the spacer). I need to maintain close to this amount with the 9.5" wheel. So if the center point (0 offset) is 4.75" I need to move the wheel in .75" or +19mm. Coincidently 20mm is pretty common... This will fit nicely on the inside but what about the outside? Right now I have 5.5" of wheel on the inside of the mounting surface and 2.5" on the outside. With the 1.5" spacer there is effectively 4" on the outside. The 9.5" wheel with 5.5" on the inside should leave the same 4" on the outside.

In typing this I think that I have convinced myself, if you think that I am crazy please stop me from making a bad purchase...