Questions about SLC wheel offset and carbon ceramic conversion

So thought I would break this into a new thread, but it is really part of my build log.

I am in the process of converting my Gen 1 rear and front upright over to C7 hubs, sing the very good information on the SLC hubs race worthy thread. While looking for C7 hubs, I found a a very good deal on a set of C7 carbon ceramic rotors and calipers, and I just went for it.

So, I have read that you must use 20 inch rims on the front to be able to fit over the rotors and calipers. This just seems odd, because if I use OEM Z06 rims, shouldn't they clear the brakes?

I was looking at these rims, if I wanted something stock looking https://www.corvettegarage.com/c7-corvette-wheels/gm/c7-z06-corvette-wheels/
20x12 rear, 19x10 front. Offset rear is +59 rear, +43 front. Rims and tires should fit similar to forgestars for the SLC.

Or maybe these if I go full custom. https://www.vicrez.com/brixton-jo01-forged-wheel-vzn100535 these rims can be built to almost any specification.

Then I found this thread, that there are 18 inch forgestars that clear the carbon ceramics....https://www.corvetteforum.com/forums/c7-z06-discussion/4264675-18-rims-that-clear-carbon-ceramics.html

It's confusing to say the least.

So my question is what is the stock SLC offset front and back. Because as I make the hub adaptors for the uprights, I am pretty sure I can change the stock offset at least .6" either direction. Keep in mind I am having custom axles made so no need to worry about existing parts working. Ideally, I would want the car to be able to accept C7 Z06 rims, and there are an endless number of variants for this setup.

Thanks.

Bob
 

Ken Roberts

Supporter
With the kind of torque your setup will produce I would definitely consider a forged wheel instead. The stock C7 Z06 wheels are prone to cracking. I read about it all the time on the Corvette Forum. (there is a current class action lawsuit in the works over it)

It’s usually the face of the wheel on the inside surface that is the culprit for large rotor/caliper interference. Some Forgestar wheels in 18” size will actually fit with the larger C7 Z06 caliper. I think it’s the CF5 model.

The stock OEM offset of the C6 and C7 Z06 wheels is +40front and +59rear. The width is 9 1/2” front and 12” rear

The stock OEM offset for the C7 ZR1 is +42front and +59rear. The width is 10 1/2” front and 12” rear.

The offset of RCR provided wheels is usually +30front and +57rear. (note that some cars received 9 1/2” front wheels and some get 10” front wheels).

I don’t know the offsets of the optional front and rear 18” CCW forged wheels. Fronts were 11” and rears were 13”.

Your C7 Z06 Calipers will most likely not be a direct bolt on. You will need to make adapters. Fran has previously sold special uprights made for use with C6 ZR1 calipers.
 
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Ken Roberts

Supporter
You can manipulate the offset of the C7 hubs as you say but keep in mind that the brake caliper is directly mounted to the upright. This means that it will also need to be changed the same amount. Since you will be most likely making adapters for your C7 Z06 calipers than this can be factored into the design.
 

Ken Roberts

Supporter
The C6 and C7 optional Cup wheels will fit your caliper/ceramic rotor combination and the C7 Zr1 wheel (pictured) will fit as well. Neither is a forge wheel though. Lots of them for sale however.

The pictured set of OEM C7 ZR1 hyper silver wheels can be had for $1750 buy it now on EBay.

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Ken,

Thanks. Great info. Was planning to have to make adaptors for the calipers, should have added that. Looks like on the rear I can just use a slightly thinner spacer, 2 mm --~.078 inch and get he same offset as the Z06/ZR1 which brings up another point. Some people are using 0.19 inch spacers on the rear, other .25", there seems to be some debate with measurements taken with the hub stub shaft bolted in vs not. Not to concerned about this one, as I doubt a 2 mm variation is going to effect the rear end much either way.

As to the front, a gain of 10-12 mm seems really significant. Basically it would mean not using a spacer, and bolting the hub right to the upright. But if some SLC's get 9.5" and others 10" front tires, there must be at least 0.5" of clearance from tire edge to frame in there. I suspect the stock SLC 18 and 19" rims do not have the rim to outside caliper clearance.

So, on the rear end I will make my hub adapter 2 mm shorter, on the front I guess try not using the spacer at all. I will investigate the forgestar 18's. in my experience with teslas, the meatier tire is the better choice.

The rear is the most pressing issue, not ready to tackle the front end yet.
 

Ken Roberts

Supporter
I was the first to modify the newer generation of rear upright. I used a .190” plate of aluminum to make the spacer. When assembled and measured against the original C4 hub there was only about .007” difference. A better thickness for the spacer would have been .200” instead but that would mean machining a thicker sheet down to .200”. I elected to keep it simple and just buy a readily available .190” sheet from McMaster Carr.

Aaron just finished his rear hub install and used a .205” spacer. Roger Reid was the builder who used a .250” spacer. He didn’t have his stub shaft torqued to his C4 wheel hub when he compared measurements.

Roger Reid or Ron McCall were the first to come up with the idea of making the spacer and bushing as one piece.

Your build is over the top. Amazing!
 
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Here are the Z06/ZR1 - 393mm Carbon Ceramic rotors on my GT40. I can squeeze an 18" rim over them.

Full disclosure, I designed the brake caliper mounts to suit, and there is around 3mm between the caliper and the inner rim, but it does fit. These wheel inners are dead straight behind the mounting face, so any wheel that tapers would not work. The rears are 380mm rotors, so no issues there. 19" should be safe, but I'm not 100% sure of the brake position on the SLC upright.

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Troy,

Just checked out your build log. What a chassis! Love the shock mounts and bell cranks. I considered doing a similar design on the rear end of the SLC. Just cut it off and redesign it....but thought it was going to far. Thanks for the photos. Big help.
 

Scott

Lifetime Supporter
Bob,

To register in MA you will need to go through a salvage inspection with a State Trooper. You need receipts for the parts. Any part that came from a donor car must have the donor car's VIN on the receipt. If the part came from a race car without a VIN number I'd have that clearly marked on the receipt. If you purchased the part from an individual I'd have a notarized one-page affidavit with all of the relevant information. I had a cobra insured and registered to me in NJ for 20+ years and when I went to register it in MA, I had to go through this process as though the car were new. Their assumption is that the parts are stolen until you prove otherwise.
 

Fran Hall RCR

Moderator
GT40s Sponsor
Bob,
we've made different uprights to accommodate the mounting of the ZR1 brakes on an SLC but not for an 18 inch wheel package.

There's a very good reason that chassis bears a striking resemblance to both an RCR40 and an SLC ;)
 
I hear ya Scott.... MA is the worst for this hobby. I suspect by the time I am done I will have a VT or NH address. But I have been getting vin`Ed receipts. Most of my build is new in box so far. The motors and now the brakes re the only used parts.





Bob,

To register in MA you will need to go through a salvage inspection with a State Trooper. You need receipts for the parts. Any part that came from a donor car must have the donor car's VIN on the receipt. If the part came from a race car without a VIN number I'd have that clearly marked on the receipt. If you purchased the part from an individual I'd have a notarized one-page affidavit with all of the relevant information. I had a cobra insured and registered to me in NJ for 20+ years and when I went to register it in MA, I had to go through this process as though the car were new. Their assumption is that the parts are stolen until you prove otherwise.
 
Oh, I saw the influence. I suspect some cut and paste was involved.



Bob,
we've made different uprights to accommodate the mounting of the ZR1 brakes on an SLC but not for an 18 inch wheel package.

There's a very good reason that chassis bears a striking resemblance to both an RCR40 and an SLC ;)
 
So got the c7 z06 rotors and calipers yesterday. They are very similar to the existing rotors. Distance from bottom of rotor to mounting surface is identical. They actually fit inside my 18 inch ccw's, barely. About .55 inch clearance. Just need a different caliper mount. So going to keep the stock slc offset for the hub spacer, and stick with the 18s, or go with the slc 20/19 inch set if I run into problems on the front.
 

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