Wheel offset calculation - need help checking math

[desertfox73]

I'm looking at a set of new wheels for my F85 and need someone (or everyone) to check my math regarding offsets on the new rear wheels since they are wider than stock and I want them to sit flush without spacers.

Current stock rear wheels are 11.5" wide with offsets of +38.

The wheels I am buying are 12" wide, and I'd like the outer edge of the rim to sit about 20mm outside of where the stock wheels sit. I can customize the offsets, which I need help calculating.

So here's the math as I figure it:

stock wheel
width = 292mm
width of rim from center = 292/2 = 146mm
stock offset = 38mm
amount of rim extending out from hub face = 146-38 = 108mm
adding the 20mm to where the wheel looks flush = 128mm

new wheel
width = 305mm
width of rim from center = 305/2 = 152.5
to get 128mm from hub face to outer edge = 152.5-128 = 24.5mm
ideal offsets of 12" width wheel should be +24.5 (round to 25)

Does that seem right?

[Ehloo]

Are you lowering the car? If you truly want a flush fitment when the top of the wheel sits at the fender including camber and alignment you will need to be in the et 15 range. I am been trying to find the best combo for awhile and finally found that between 10-15 et is ideal. If you are not lowering and very low that recommendation would be too aggresive. I am running a 22x12 with a 15 et

Originally Posted by desertfox73

I'm looking at a set of new wheels for my F85 and need someone (or everyone) to check my math regarding offsets on the new rear wheels since they are wider than stock and I want them to sit flush without spacers.

Current stock rear wheels are 11.5" wide with offsets of +38.

The wheels I am buying are 12" wide, and I'd like the outer edge of the rim to sit about 20mm outside of where the stock wheels sit. I can customize the offsets, which I need help calculating.

So here's the math as I figure it:

stock wheel
width = 292mm
width of rim from center = 292/2 = 146mm
stock offset = 38mm
amount of rim extending out from hub face = 146-38 = 108mm
adding the 20mm to where the wheel looks flush = 128mm

new wheel
width = 305mm
width of rim from center = 305/2 = 152.5
to get 128mm from hub face to outer edge = 152.5-128 = 24.5mm
ideal offsets of 12" width wheel should be +24.5 (round to 25)

Does that seem right?

[desertfox73]

Originally Posted by Ehloo

Are you lowering the car? If you truly want a flush fitment when the top of the wheel sits at the fender including camber and alignment you will need to be in the et 15 range. I am been trying to find the best combo for awhile and finally found that between 10-15 et is ideal. If you are not lowering and very low that recommendation would be too aggresive. I am running a 22x12 with a 15 et

Great question - at the moment, I'm not planning to lower the car.

[AECDY]

Your calculations look correct. See below (Tires specs might not be exactly what you have but it gives you an idea on how much will it poke)

https://www.willtheyfit.com/index.ph...#38;offset2=25

[desertfox73]

Originally Posted by AECDY

Your calculations look correct. See below (Tires specs might not be exactly what you have but it gives you an idea on how much will it poke)

https://www.willtheyfit.com/index.ph...=12&offset2=25

Thanks - seeing the "poke" value is really helpful. Hadn't used that tool before.