what is correct offset for 11x17" fuch on 930

[jwakil]

I'm ordering some repro Fuch's 11x17 rear wheels for my 1981 930. Want to make sure the offsets are correct. I was told that the offset should be zero if I don't use the factory spacer in the rear. Does this sound correct?

[Bill Verburg]

Originally Posted by jwakil

I'm ordering some repro Fuch's 11x17 rear wheels for my 1981 930. Want to make sure the offsets are correct. I was told that the offset should be zero if I don't use the factory spacer in the rear. Does this sound correct?

what wheel do you have now? Fuchs 8 ET10.6? and are you using the oe 28mm spacer now?

[jwakil]

Originally Posted by Bill Verburg

what wheel do you have now? Fuchs 8 ET10.6? and are you using the oe 28mm spacer now?

Yes, it is the stock 8" Fuch with stock spacer, and 28mm sounds right.

[Bill Verburg]

Originally Posted by jwakil

Yes, it is the stock 8" Fuch with stock spacer, and 28mm sounds right.

Ok, an 11 ET12 will place the outer edge of the wheel where the current 8 w/ spacer is
8ET10.6 w/ 28mm spacer front space is ~5.5", 11ET12 w/ no spacer has a front space of ~5.5"

If you want the wheel more outboard reduce the ET, 11ET0 puts the outer edge 12mm more outboard.

For this purpose backspace doesn't matter as there is an abundance of room in back

[jwakil]

Originally Posted by Bill Verburg

Ok, an 11 ET12 will place the outer edge of the wheel where the current 8 w/ spacer is
8ET10.6 w/ 28mm spacer front space is ~5.5", 11ET12 w/ no spacer has a front space of ~5.5"

If you want the wheel more outboard reduce the ET, 11ET0 puts the outer edge 12mm more outboard.

For this purpose backspace doesn't matter as there is an abundance of room in back

Damn, my head is hurting....Your numbers sound right, but I don't know why my logic is not agreeing. Let's assume I'm keeping the spacer. If I want the outer edge of the wheel in the same place, going from 8" to 11" moves the centerline 3"/2=1.5"=38mm inboard. That means the offset for the 11" would be 10.6+38 = ~48. Now, if I get rid of the 28mm spacer I get 48-28 =ET20? This says ET20 would put the outer edge at same place, and ET0 would move the front edge 20mm.

[Bill Verburg]

Originally Posted by jwakil

Damn, my head is hurting....Your numbers sound right, but I don't know why my logic is not agreeing. Let's assume I'm keeping the spacer. If I want the outer edge of the wheel in the same place, going from 8" to 11" moves the centerline 3"/2=1.5"=38mm inboard. That means the offset for the 11" would be 10.6+38 = ~48. Now, if I get rid of the 28mm spacer I get 48-28 =ET20? This says ET20 would put the outer edge at same place, and ET0 would move the front edge 20mm.

ET = BS -.5*OA or ET = .5*OA - FS either works and gives the correct sign

you can even do the calc w/ a mounted tire by using the tire section width instead of the wheel overall width

What you have now is a 8ET -17.4 w/ ~5.06" fs and 3.69" bs for 8.75" oa(Fuchs have 3/8" flanges))

I think that I may have run the #'s is the earlier post w/ a 9 instead of an 8, but the fs will be close for either

ok w/ the 28mm spacer here's what happens
an 11ET25 has the same fs, that would be an 11 ET53 w/ 28mm which is the same as an 11ET25, fs for this is 5.02" and bs is 6.98( if the wheels have the usual .5" flanges, Fuchs only have 3/8" flanges and BBS are in between)

my ET25 is different from you ET20 probably because of the flange width