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Wheel swap

Old 10-10-2018, 09:17 AM
  #21  
emarkovits
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The C5 only has its stock wheel and not the C5Z06 wheels. In addition they are not 4 same width wheels, I plan to use in the future. The C5 will run 4 same wheels 18x10.5 with 315 wide tires. I plan to buy the wheels and tires for the C5 (which is being built to be a Spec Vette race car). In the mean time, I was hoping to use the new C5 ZO6 wheel/tires set up on the 1995 C4 I'm currently running next couple months.

I think after all the discusison, it appears I would need to use 20mm hub centric spacers on the C4 to have the same location and results as my current 17x11" wheels I currently use on C4.

Long story but hope it makes sense.
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Old 10-10-2018, 10:15 AM
  #22  
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ah, that makes more sense.
I thought you were needing some coffee or something.
(and sorry, I might come off as a dick before my morning coffee )
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Old 10-11-2018, 03:35 PM
  #23  
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Originally Posted by MatthewMiller View Post
Something is odd here. The front C5Z wheel is 17x9.5 with offset of 54mm, which gives backspacing of only 7.38". That's almost identical to a stock C4 17x9.5 that has offset of 56mm. They should fit just fine. The rear C5Z is 18x10.5 with 58mm offset, and will have 8.03" of backspacing. That's about the max backspacing that will fit on a later C4, but it should fit on all four corners. Note that I have three sets of wheels with similar backspacing and they fit just fine. Certainly though, running 1/4" spacers would not be a problem if needed.
I was only referring to the 18x10.5 wheels that i test fit on both front and back of my car.
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Old 12-08-2018, 12:05 PM
  #24  
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Hey guys, I have someone who wants to buy a set of C7 base wheels (18x8.5 +56 / 19x10 +79) from me to put on his 87 C4. I had him bring his car by to do a test fit. The front wheel bolted on with no clearance issues. The rear was hitting some suspension parts and would not let the wheel seat on the hub. It was about 3/8" away from seating. Has anyone done this successfully using spacers or adaptors. Hanging past the quarters panel is not a factor. Any info or direction is appreciated.
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Old 12-08-2018, 12:24 PM
  #25  
MatthewMiller
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Originally Posted by Jmcdude View Post
Hey guys, I have someone who wants to buy a set of C7 base wheels (18x8.5 +56 / 19x10 +79) from me to put on his 87 C4. I had him bring his car by to do a test fit. The front wheel bolted on with no clearance issues. The rear was hitting some suspension parts and would not let the wheel seat on the hub. It was about 3/8" away from seating. Has anyone done this successfully using spacers or adaptors. Hanging past the quarters panel is not a factor. Any info or direction is appreciated.
8.5" wheels on the early C4s (84-87) only used 32mm offset. Those hub faces were further in on each side than on the later C4s, which used 56mm offset for the 8.5" wheels. That's an inch of difference in offset up front - quite a bit. I'm actually surprised you even got the fronts to fit! They must have been set in quite a bit. Did you check their clearance with the steering turned to full lock in both directions? You should consider 1" spacers for the fronts: even if they physically fit, they will look a lot better with the proper offset.

For the rear, your 10" ET79 wheels have 8.61" of backspacing. The original 16x9.5" ET38 1987 C4 wheels had only 6.75, so there's more than 2" difference in backspacing . That explains the interference. Your friend will probably need 1.5-2" adapters to use those wheels.
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Old 12-08-2018, 12:58 PM
  #26  
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Thanks for the reply Matthew. His car has the 16 x 9.5 salad shooters. How does that change your calculations? We did not test the fronts with the steering turned for clearances. Probably should have but we were doing it outside and it was about 25 degrees at the time.
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Old 12-08-2018, 01:13 PM
  #27  
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Originally Posted by Jmcdude View Post
Thanks for the reply Matthew. His car has the 16 x 9.5 salad shooters. How does that change your calculations? We did not test the fronts with the steering turned for clearances. Probably should have but we were doing it outside and it was about 25 degrees at the time.
It has the 16x9.5" ET38 wheels all around, like these, right?


I believe we refer to those as "Turbine" wheels, just for clarity's sake.

"Salad Shooters" came around after the new suspension took over in 1988. They are 17x9.5 ET56, and look like this:



It doesn't the change the calculations, though. All 84-87 C4s have the same amount of clearance and offset requirements. Your C7 front wheels are narrow enough that they only have 6.95" backspacing, even with 56mm offset. They might just barely clear the suspension and inner fender liner at full steering lock, but even so IMO they are going to look rather strange being set in so far. I think he'll still want that 1" spacer up front.
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Old 12-08-2018, 01:32 PM
  #28  
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He has the top set which you referred to as turbines. I am not up with the names of those older wheels. A search a Ebay showed them as salad shooters. The 1" spacers make sense and would assure turning clearance so that's a go. I had said that sticking out beyond the quarters was not a concern, but that's when I was thinking 3/4" would do it. At 1 1/2 -2" that has me wondering just how much that would push the wheel past the quarter?
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Old 12-08-2018, 02:02 PM
  #29  
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Originally Posted by Jmcdude View Post
He has the top set which you referred to as turbines. I am not up with the names of those older wheels. A search a Ebay showed them as salad shooters.
No worries about that at all. I just wanted to make sure we're talking about the same thing.

The 1" spacers make sense and would assure turning clearance so that's a go. I had said that sticking out beyond the quarters was not a concern, but that's when I was thinking 3/4" would do it. At 1 1/2 -2" that has me wondering just how much that would push the wheel past the quarter?
Even a 2" spacer shouldn't push wheel past the edge of the fender (called "poke") at all. On the rear, the original Turbines have 6.75" backspacing and your C7 10" wheels have 8.61" backspacing, which 1.86" more. So with no spacers (if you could actually mount them), the outer lip of the C7 wheel would sit 1.36" inside of where the outer edge sits with the Turbine mounted. If you had 1.86" spacers (not that they exist), you'd net a backspacing with the C7s that is identical to the Turbines, and the outer edge would sit 1/2" further out toward the fender edge. That should still be completely inside the fender lip. With a 1.5" spacer the C7 wheel's outer lip will be further 0.14" out than the Turbine wheel (~1/8"), and with a 2" spacer it will still only be 0.64" (~2/3") further out than the Turbine wheel. So it should stay tucked fully inside the fender either way.

You can probably test the above by getting a stack of washers that fit the studs. Stack them on at least three wheel studs, first so they make a 1/8" of spacing and then stack them to 2/3". Fit the stock Turbine wheels with each washer stack thickness and note where the outside edges of the wheel and tire sit with each. If he likes it best with 1/8" washer stacks, then he can use the 1.5" adapters. If he likes it better with the 2/3" stacks, then he wants 2" adapters.

One disclaimer here: I don't know if adapters exist in 1.5" or 2" spacings. That's a lot of spacing! OTOH, since it would keep the wheel/tire's total offset (combining the wheel offset and the spacer dimensions) similar to stock, it will keep proper suspension geometry and shouldn't wear the wheel bearings any more than the stock wheels.
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Old 12-08-2018, 02:53 PM
  #30  
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Matthew, I appreciate your help on this matter. I found this video on youtube where a guy did this same swap. Don't pay much attention to what he says, but his C7 wheels are the same specs as mine. He doesn't mention what size the adapters are, but looking at the part where he shows the new wheels installed, the fronts adapters appear to be around an inch and the rears are much thicker, close to 2" as you said. I think I have the info we need to get them to fit properly. Thank you very much.

You can skip the crap at the beginning and start at the 4:00 minute mark to see the installation details.
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Old 12-08-2018, 03:50 PM
  #31  
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Originally Posted by Jmcdude View Post
Matthew, I appreciate your help on this matter. I found this video on youtube where a guy did this same swap. Don't pay much attention to what he says, but his C7 wheels are the same specs as mine. He doesn't mention what size the adapters are, but looking at the part where he shows the new wheels installed, the fronts adapters appear to be around an inch and the rears are much thicker, close to 2" as you said. I think I have the info we need to get them to fit properly. Thank you very much.
That actually appears to a later C4 (88-96) chassis and suspension, so he could get away with less spacer than you can. OTOH, I guess he's not going to have fenders, so he can space them further out and not worry about poke. But yeah, overall the major point is that he's using very different thickness spacers front and rear. Tell us how things work out for you!
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