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C4 -> C5 brake conversion, wheel fitting

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Old 01-22-2018, 02:53 PM
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kael
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Default C4 -> C5 brake conversion, wheel fitting

Howdy, decided to chase front C5 brakes on my '87, have to replace front calipers anyway. I know about the adapters (see https://www.corvetteforum.com/forums...-brackets.html if you don't).

I'm checking, will the conversion with stock C5 calipers actually fit in my wheels? I know generally recommendation is 17" wheels. But I think it's likely that's in terms of typical Corvette wheels, replicas, etc. I purchased custom wheels and not sure the various bits allow enough space. They are 18", don't want to spend several hundred dollars to find out "Whoops, rim is too small".

So, hoping for dimensions of a finished C5 setup:

- Radius from center hub to outside shell of caliper.
- Height from face of hub to farthest outside shell of caliper. Pretty sure the caliper is out more than the hub.
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Old 01-22-2018, 04:46 PM
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I believe you will need A molds, c5, or aftermarket to fit. The J55 C4 caliper is tight to the stock saw blades.
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Old 01-23-2018, 12:25 AM
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Originally Posted by kael View Post
Howdy, decided to chase front C5 brakes on my '87, have to replace front calipers anyway. I know about the adapters (see https://www.corvetteforum.com/forums...-brackets.html if you don't).

I'm checking, will the conversion with stock C5 calipers actually fit in my wheels? I know generally recommendation is 17" wheels. But I think it's likely that's in terms of typical Corvette wheels, replicas, etc. I purchased custom wheels and not sure the various bits allow enough space. They are 18", don't want to spend several hundred dollars to find out "Whoops, rim is too small".

So, hoping for dimensions of a finished C5 setup:

- Radius from center hub to outside shell of caliper.
- Height from face of hub to farthest outside shell of caliper. Pretty sure the caliper is out more than the hub.
What kind of aftermarket 18" wheels do you have?
At 18" you should have all the clearance you need for C5 brakes!
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Old 01-23-2018, 05:24 PM
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Originally Posted by mako41 View Post
What kind of aftermarket 18" wheels do you have?
At 18" you should have all the clearance you need for C5 brakes!
Yes, when I more carefully measure the inside diameter and did the math right (7+7 is 12?), I felt much better about that. Concern is the height, as measured from the plane of the rotor. The spokes of the rim falls back at the outer edge, need to make sure that clears the caliper with some room. Probably is fine, but there's a few dollars involved.

Wheels are Advanti Racing Kudos.
http://www.advantiwheel.com/wheel/a4-kudos-silver/
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Old 01-23-2018, 06:21 PM
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Originally Posted by kael View Post

Wheels are Advanti Racing Kudos.
http://www.advantiwheel.com/wheel/a4-kudos-silver/
You've already bought these? Width and offset of what you've bought.

Those wheels actually don't have a C4 Corvette bolt circle. They would require a 'force-fit' to accomplish even a 'bolt-on'.

I doubt there's an Advanti Wheel available for a 5 X 4 3/4 (5 X 120.65) bolt circle.

Last edited by WVZR-1; 01-23-2018 at 06:35 PM.
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Old 01-23-2018, 06:42 PM
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Originally Posted by WVZR-1 View Post
Those wheels actually don't have a C4 Corvette bolt circle. They would require a 'force-fit' to accomplish even a 'bolt-on'.
The correct bolt pattern is 5x120.65 or 5x4-3/4". The 120mm is typical of a BMW wheel. Also what is the offset of the wheels you now have?. The stock '87 wheels have an offset of 36mm or 38mm depending on the rim width. Typical later C4 and C5 front wheels will have a 56mm offset. Without adapters, wheels with that 56mm offset will fit a good 3/4" further into the wheelwell.

When I had my '87 and installed C5 front brakes, I used aftermarket ZR-1 style 5-spokes and had no clearance issues at all with caliper clearance. But the wheels I bought had the correct 38mm offset and the correct bolt pattern. Another thing I did with the upgrade was to install a different front brake bias spring. This fixed a tendency for the rear brakes to lock up before the fronts. I got it from Doug Rippie Motorsports for about $25.
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Old 01-24-2018, 10:10 PM
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Yes, the Advanti's fit 5x4.75. They are advertised as 5x120mm and as 5x120.65mm. I put one on my hub to make sure and my eyeball didn't see one stud out of center. I've heard others don't have a problem using 120's. Think about, .65mm split, in inches thats .013, lug nuts have many scars deeper than that. Your mileage may vary, etc etc.

These are 18x9.5, +40mm offset, where my Lady is a z52 with +38. I've also heard others mention that the 2mm doesn't change much, 2mm further in board, but I'll wait until I see what I see. There are 2mm plates available to decrease the offset. Certain later models use 40mm offset, gives some of us early C4 folks some new choices of rims.

I'm a engineer-wanna-be (well, more an engineer graduate who switched to computers), I don't like the "buy-n-try" method, prefer to check basic specs first.

Well, I'll chase more specs somewhere and pull the trigger.
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Old 01-25-2018, 05:57 PM
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Originally Posted by kael View Post
Yes, the Advanti's fit 5x4.75. They are advertised as 5x120mm and as 5x120.65mm. I put one on my hub to make sure and my eyeball didn't see one stud out of center. I've heard others don't have a problem using 120's. Think about, .65mm split, in inches thats .013, lug nuts have many scars deeper than that. Your mileage may vary, etc etc.

These are 18x9.5, +40mm offset, where my Lady is a z52 with +38. I've also heard others mention that the 2mm doesn't change much, 2mm further in board, but I'll wait until I see what I see. There are 2mm plates available to decrease the offset. Certain later models use 40mm offset, gives some of us early C4 folks some new choices of rims.

I'm a engineer-wanna-be (well, more an engineer graduate who switched to computers), I don't like the "buy-n-try" method, prefer to check basic specs first.

Well, I'll chase more specs somewhere and pull the trigger.
Well if those 18" aftermarket wheels do in fact have the correct Chevy bolt pattern with a +40mm offset you should not have any problems clearing C5 brakes at all.

Last edited by mako41; 01-25-2018 at 05:57 PM.
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Old 01-26-2018, 08:18 AM
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OP - It's difficult to tell if you actually have the wheels 'in hand' or NOT. Some things you don't seem to get. Very dependent upon the center bore of the wheel could determine how effectively you could 'force-fit' these 5 X 120 wheels. You hint that you have 5 X 120.67 but then seem to mention you don't care because there's no difference, well there is. I didn't see a 5 X 120.67 option for any of their product.
Part# of what you bought maybe?

A quick glance of the product displayed no specifications of the wheel bore. If you have them 'in hand' measure and post back. Your C4 hub is 70.3 +/-. If less than that there's for sure a "NO FIT" and if it's substantially larger than the 70.3 then without the use of 'hub rings' you've no way to actually center the wheel on the hub effectively.

The 40mm off-set I'd think not an issue and regarding caliper to wheel spoke clearance that's generally something you measure yourself and don't rely upon others to furnish. If you don't understand how to measure your wheels for spoke clearance - LEARN!!!

User 76LS1BIRD might be able to supply you dimensions and likely also higher quality adapters than some offer. I'd reach out to him.

Last edited by WVZR-1; 01-26-2018 at 08:28 AM.
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Old 01-26-2018, 04:40 PM
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WVZR-1, you need to read more carefully.

And yeah, hub bore rings were purchased, installed and mounted just fine.
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Old 01-26-2018, 05:18 PM
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Originally Posted by kael View Post
WVZR-1, you need to read more carefully.

And yeah, hub bore rings were purchased, installed and mounted just fine.
I don't believe I missed a thing - you've posted a bunch of confusing things.

The caliper spoke clearance you need should be simple enough if you have calipers & pads. Install 1 pad in caliper , measure from friction surface of pad to caliper edge and compare that dimension to, 45.47 (rotor hat height) - 32.00 (rotor friction thickness) [13.47], anything in excess of that dimension I'd think is what you'll need 'minimum' for spoke height. Hat height is sometimes rounded to 46 I think for C5.

Rotor is 325 so add maybe 30 to that [355] / 2 = 177.5 for the radius you're looking for. If you've got substantial clearance in excess of those I'd think you don't need to be concerned. Numbers close I'd say you 'buy and try'.

You could get anyone with a C5 or a C4 (w/C5 conversion, doesn't matter year) to measure but then you need to confirm anyway.

Do you have caliper and pads? You don't need rotor or brackets.

I believe the math is maybe correct - I only did it once. I might do it again later.

c4cruiser did his back in maybe '09 and here's a couple snapshots he took of his. Knowing that the rotor is 32 thick and 325 diameter I believe you should be able to 'approximate' for your wheel clearance dimensions. Maybe he's got more snapshots or advice he can pass on. I'm just using his to sorta validate the method I suggested to use for measuring. If you don't have brackets I'd see 76LS1BIRD

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Last edited by WVZR-1; 01-27-2018 at 07:31 AM.
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Old 01-28-2018, 12:02 PM
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You miss a simple item: I have not purchased brakes. I have the wheels, as I wanted, I'm chasing could I upgrade to C5 brakes. I have to replace mine anyway, mishap due to lack of thread lock.

FYI, always put RED threadlock on your bracket bolts! Or else!

I know the diameter of all is fine, the concern is what's shown in the second pic (thanks for that). Considering the the outer rotor surface as the floor, how tall is the caliper? From the pics, it's hard to tell, it almost looks like the outside edge is even with the hub face (as in where the rotor touches the wheel), which would be good for these wheels UNLESS it was too close the inner face of the wheel, the spokes turn inward close to that, almost even with the hub face.

The pic does confirm another piece though, the face of the caliper does stick out past the bracket, I wasn't sure which was further out. I happened to get used brackets from cep39 this week.

Guess either these fit or there will be some conversion bits for sale soon.
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Old 01-31-2018, 05:50 PM
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Finally got adapters and tried bracket test. Initial reaction is no go.
Basic clearance is about a finger clearance of the bracket, guessing caliper might stick out too far.

Another thought, are the brackets I bought, used, the bigger size, 13"? Note these are 8" OC at caliper pins.

Opinions? Maybe a 2-3mm spacer might work?

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Old 01-31-2018, 06:46 PM
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The dimension you're measuring on the abutment bracket has absolutely nothing to do with your needs.

Lay a flat edge across the wheel flange that's 15" long and take snapshots of the back of the wheel. Measure 'flat edge' to spoke from the hub diameter at each 1" increment to the end of the flat edge.

I'd be interested in seeing good snapshots of the wheel back-side.
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Old 04-17-2018, 03:59 PM
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I finally went to just get the dang calipers and adapter and try it out.

Important fact presented:
It might be a good idea to include the ROTOR for test fitting....
One Dumb *** Right Here.
Golly, several mm might mean something? DOH!!

Well, at least now I see 2mm clearance to the caliper bumps without a spacer.
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Old 05-16-2018, 04:53 PM
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Profile information from my completed setup.
Keep in mind my adapter had to be flipped to center the bracket.
https://www.corvetteforum.com/forums...-measured.html
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