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...

Ok, correct me if I'm wrong, it's been awhile since I calculated offset for my S10 wheels but I'll give it a shot here.

13mm (roughly, it's like 13.2 I believe) is 0.5 inches.
26mm is 1 inch

SOOO... the wheels you have on there now, if they had the spacer built into the hub, would be near a 0 offset. (26+13=39mm spacer -40mm offset)

In your instance we have to calculate backspace in order to get the right distance to the outside of the car (so they don't stick out like your Mexican homie's Daytons down the street). Your old wheels (w/ spacer built in) would have a 4inch backspace or distance from the face of the hub to the inside of the wheel. This backspace distance is the same as the distance from the face of the hub to the outside of the wheel as well. This is what we're concerned with. So, you want to keep the same distance from the face of the hub to the outside lip of the wheel with 9.5in wheel. Lets do some geek math.

9.5/2=4.75 4.75 is our 0 offset point
Since backspace is measured from the face of the hub to the INSIDE of the wheel, we need to figure out what ideal backspace would be while keeping a 4inch distance between the face of the hub and the outside of the wheel. 9.5-4=5.5 5.5 will be the correct backspace for the new wheels. Lets convert it to offset shall we?

5.5-4.75=.75 .75 is our offset OR right near +20mm (26*.75=20 roughly)

You will need a 18x9.5 wheel with a +20mm offset or 5.5 backspace
most wheel companies don't list the backspace so it's usually best to use the offset as your guide.

Just as a guess, I don't think the 18x10's will fit if you need any more space than the current 5.5 backspace wheels provide without the spacer because that extra .5in will have to go on the inside to keep the same flush look on the outside.

Any questions class? LOL

Thanks for taking the time to run through that!

It would appear that we both arrived at the same calculation. Since I have the widebody kit the idea is to give it the triple gold Dayton homie look. The current spacers kick the wheels out 1.5 inches so that they are flush with the new body surface.

If I find 10" wheels first I think I could get away with another 1/2 inch on the outside. I will just have to make sure that I keep the backspacing correct and hang the extra 1/2 inch on the outside. With the new width giving a 0 offset of 5" I would only need ~+13 offset. I have seen some +12s listed for some wheels but I think I like the 9.5" idea...

thanks again!

no problemo