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Fikse ZFs - 17” Rear Wheels... 9.0 or 9.5 inches?

 
Old 11-24-2018, 01:59 PM
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August West
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Default Fikse ZFs - 17” Rear Wheels... 9.0 or 9.5 inches?

I’m ordering up a set of Fikse ZFs and was hoping for some guidance as to whether I should get 9.0 or 9.5 inch rear wheels for my narrow body 1990 C4? Is one better than the other for tire sizes? I’d also like the proper offsets so I won’t need spacers. I’ll be running 8.0s in front. Thanks in advance!
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Old 11-24-2018, 03:51 PM
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Bill Verburg
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Originally Posted by August West View Post
I’m ordering up a set of Fikse ZFs and was hoping for some guidance as to whether I should get 9.0 or 9.5 inch rear wheels for my narrow body 1990 C4? Is one better than the other for tire sizes? I’d also like the proper offsets so I won’t need spacers. I’ll be running 8.0s in front. Thanks in advance!
Factory ran 205/50 & 255/40 on 7ET55 & 9ET55
You can run 225/45 on 8 ET50 or 52 & 255/40 x17 on 9ET55 or on 9.5ET47, this latter was used on 964 Cup.

W/ AWD the concern is matching f/r tire rolling radius
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Old 11-24-2018, 04:49 PM
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Thanks for the reply, Bill. I suppose offsets are specific to particular wheels... the offsets for Cup 1s would be different from the offsets for Fuchs-style replica wheels. Is that correct?
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Old 11-24-2018, 04:51 PM
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...and thanks for the reminder about F/R rolling radii on the C4... within 6% of each other IIRC.
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Old 11-24-2018, 07:57 PM
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Originally Posted by August West View Post
Thanks for the reply, Bill. I suppose offsets are specific to particular wheels... the offsets for Cup 1s would be different from the offsets for Fuchs-style replica wheels. Is that correct?
The ET(offsets) is correlated to the wheel width and how aggressive a fitment you want.

For instance an 8ET59 is slightly more aggressive than an 8ET52, another example a 7.5ET45 is comparable in fit wrt the lip to an 8ET52
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Old 11-24-2018, 07:58 PM
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Originally Posted by August West View Post
...and thanks for the reminder about F/R rolling radii on the C4... within 6% of each other IIRC.
I'd need to look it up but I think that ABS spec is w/i ~5%, the envelope for AWD is tighter
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Old 11-25-2018, 12:38 AM
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I used to run 8" front and 10" rear on my C4 but now run 8.5" in front and there is a noticeable difference with turn in with ess understeer so I'd opt for 9" rear for C4 if you have 8" fronts.

Neil
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Old 11-25-2018, 03:22 AM
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Well I’ve ordered up 7.5 inch fronts and 9 inch rears. When Zuffenhaus had their webpage up, I remember them saying 7.5 inch for stock springs or 8.0 with 2.25” springs.

I’ll be sure to post when they arrive and when mounted.
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Old 11-25-2018, 03:29 AM
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Originally Posted by Bill Verburg View Post
I'd need to look it up but I think that ABS spec is w/i ~5%, the envelope for AWD is tighter
I found the 6% figure for rolling radius differential in Adrian’s book.
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Old 11-27-2018, 04:40 PM
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Originally Posted by Bill Verburg View Post
Factory ran 205/50 & 255/40 on 7ET55 & 9ET55
You can run 225/45 on 8 ET50 or 52 & 255/40 x17 on 9ET55 or on 9.5ET47, this latter was used on 964 Cup.

W/ AWD the concern is matching f/r tire rolling radius
The 9.5” Cup rear wheels will require spacers to clear the oil pipes in my experience.
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Old 11-27-2018, 06:31 PM
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Originally Posted by Atgani View Post


The 9.5” Cup rear wheels will require spacers to clear the oil pipes in my experience.
The wheels used by the factory on 964 Cup were 9.5x17ET68, They used a 21mm spacer to provide an installed ET47, Yes, all Cups had a flattened oil line.

When the switched to 19s the 9.5x18 had an ET47, No spacer used.

when used w/ a 265/35 tire the 9.5 ET47 wheel has a backspace of 7.1"(180.4mm) though I have seen 10ET ET45 used w/ 275/35x18) wheel b/s is7.27"(184.7mm) this should be considered the max b/s that can be used on a 964, the 265 tire b/s is ~7.07"(181mm) a wider tire like a 275 would have a little more backspace
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Old 11-30-2018, 03:53 PM
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Originally Posted by Bill Verburg View Post
The wheels used by the factory on 964 Cup were 9.5x17ET68, They used a 21mm spacer to provide an installed ET47, Yes, all Cups had a flattened oil line.

When the switched to 19s the 9.5x18 had an ET47, No spacer used.

when used w/ a 265/35 tire the 9.5 ET47 wheel has a backspace of 7.1"(180.4mm) though I have seen 10ET ET45 used w/ 275/35x18) wheel b/s is7.27"(184.7mm) this should be considered the max b/s that can be used on a 964, the 265 tire b/s is ~7.07"(181mm) a wider tire like a 275 would have a little more backspace
Hi Bill, running the 9.5 x 17 ET68 Cup rears with a 21mm spacer leaves a lot of clearance between the tyre and fender. I think I ended using a 28 or even 32mm rear spacer to get the standard 255/40 rear tyres to fill the fender well out nicely. See attached images of my old car running this set up.
As I recall the C2 and RS run “unflattened” oil feed/return pipes.

Last edited by Atgani; 11-30-2018 at 04:35 PM. Reason: Added images
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Old 11-30-2018, 04:57 PM
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Originally Posted by Atgani View Post






Hi Bill, running the 9.5 x 17 ET68 Cup rears with a 21mm spacer leaves a lot of clearance between the tyre and fender. I think I ended using a 28 or even 32mm rear spacer to get the standard 255/40 rear tyres to fill the fender well out nicely. See attached images of my old car running this set up.
As I recall the C2 and RS run “unflattened” oil feed/return pipes.
I just reported what the factory did

Yes, the street cars ran unflattened oil lines, but they also used 9E55 w/ 255/40 x17.. This is strange because the 9 actually has a bigger back space than the 9.5
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Old 11-30-2018, 05:13 PM
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Here's a comparison of what was used on a 964 RS and 964 Cup
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Old 12-01-2018, 04:29 AM
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Do you have to flatten the oil line with a 10” rear wheel, if you don’t lower the car too much....? Maybe a lower-than-stock-US-ride-height, but not-quite-RS-ride-height?
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