How to calculate for wheel adapters?

[Andre.servin]

I'm going to have to use wheel adapters for my car, what the formula for figuring out what size adapters you need?

wheels are 20x8.5 FR 500
BS 5.93
Offset +30
Tire size is 235/35/20

I guess the tire width is 9.3

thanks

[dontlifttoshift]

Back space you have minus back space you want equals wheel spacer thickness.

[CliffsBlueCamaro]

You have to start with what you want the backspacing (or offset) to be. What have other people used with the same width and diameter?

Then it's as simple as subtracting the desired backspace from the wheel's built-in backspace.

Here's an example.

Lots of Camaro guys run 18x9.5 wheels with 5.5" of backspacing. I know that will fit.

I find some 18x9.5 wheels listed with an offset of 22. I first have to convert the offset to backspacing by dividing the number by 25.4, and then adding it to the OVERALL width of the wheel divided by 2. (all wheels are actually 1" wider than their advertised with - 9.5" is actually 10.5".)

22 divided by 25.4 = 0.86"
10.5 divided by 2 = 5.25"
5.25" + 0.86" = 6.12"

So the wheels I want have 6.12" of backspacing built into them. I need 5.5" so...
6.12" minus 5.5" = 0.62"

I would need a 0.62" adapter/spacer.

I know it seems confusing, but after you run the numbers several times and you understand where they are coming from it starts to make sense.

If you know what a "good" backspace is for your car with that width, I can help you calculate everything.

[Andre.servin]

[QUOTE=CliffsBlueCamaro;1232537]You have to start with what you want the backspacing (or offset) to be. What have other people used with the same width and diameter?

Then it's as simple as subtracting the desired backspace from the wheel's built-in backspace.

Here's an example.

Lots of Camaro guys run 18x9.5 wheels with 5.5" of backspacing. I know that will fit.

I find some 18x9.5 wheels listed with an offset of 22. I first have to convert the offset to backspacing by dividing the number by 25.4, and then adding it to the OVERALL width of the wheel divided by 2. (all wheels are actually 1" wider than their advertised with - 9.5" is actually 10.5".)

22 divided by 25.4 = 0.86"
10.5 divided by 2 = 5.25"
5.25" + 0.86" = 6.12"

So the wheels I want have 6.12" of backspacing built into them. I need 5.5" so...
6.12" minus 5.5" = 0.62"

I would need a 0.62" adapter/spacer.

I know it seems confusing, but after you run the numbers several times and you understand where they are coming from it starts to make sense.

If you know what a "good" backspace is for your car with that width, I can help you calculate everything.[/QUOTE


Awesome man thanks for the response! I believe an acceptable BS for my car is 4.5
So doing the math 5.93-4.5=1.43 adapter? I have 2" on right now and I'm kinda getting some fender rubbing issues.

[Mr.VENGEANCE]

whos best that makes custom adapters?

[CliffsBlueCamaro]

Awesome man thanks for the response! I believe an acceptable BS for my car is 4.5
So doing the math 5.93-4.5=1.43 adapter? I have 2" on right now and I'm kinda getting some fender rubbing issues.

Your math is right on if you need to get to 4.5" backspacing with an 8.5" wide wheel.

So you already have the wheels in your first post on your car with 2" adapters? Just get a 1.5" adapter and that would likely solve your rubbing issues.

[Andre.servin]

Yes I do currently have them on with 2". I had some lying around my garage from a previous project. Cool sounds good

[Andre.servin]

whos best that makes custom adapters?

Motorsport tech

They are really nice and not too pricey. The can make them to be hub centric to the car and hub centric to the wheel as well.

I ordered from them for the rears. Just need some for the front now.