Recently it was brought to my attention that the rotors on my GTR kit were incorrectly drilled and not fit to be used. While trying to get the correct parts from RCR and becoming slightly frustrated with the process, I decided to educate myself on what makes our rotors such an oddity and see what I could do about it. I figured I would share what I learned here for posterity, as I wasn't able to find the info on forum while I was searching.
Most, but not all, GTR and SLC's utilize a C4/C5 corvette hub with studs, but the brake calipers and rotors come from a 5'th generation Camaro SS (2010-2015.). So why cant you take an off the shelf Camaro SS rotor and slap it on our cars? Well, the center hole of the rotor (or hub bore) for the Camaro won't fit the larger corvette hub that our cars use. The Camaro rotor center hole is 66.9mm, and we need the corvette size of 70.5mm so the disc can slide all the way against the hub. So... some guys will just get Camaro rotors and have the center machined out to accommodate our larger hub size.
The next problem; Although the Camaro and corvette have the exact same bolt pattern, the corvette utilizes a 12mm stud and the Camaro a 14mm stud. I've been told the industry standard is to machine the stud holes in the rotor 2mm more than needed so that the studs have 1mm of clearance on all sides when installed. In race applications, the holes are only drilled 1mm larger than needed in order to minimize movement. The concern then is that our studs are only 12mm wide, and they're going into stock Camaro drilled holes on the rotor, which are 16mm (meant for a 14mm stud). While this might not sounds like a crazy amount of slop, I'm told this is VERY unsafe. A hard slam on the brakes can cause the rotor to stop moving while the hub and studs are still in motion due to the excessive play in the 16mm holes. Over time this could weaken or sheer the studs as they aren't made to take that kind of sheering force.
The RCR solution is to take a stock Camaro SS rotor, enlarge the center hole to match what will fit our hubs, then drill an additional set of 5 holes on the rotor to match our smaller studs. In my case, and apparently a few others, the second set of drilled holes were either the larger 16mm size and not the needed 14mm set - or - some of the new holes weren't clocked correctly, creating weak points.
I plan on owning my car for a LONG time, and didn't want to rely on my memory for dimensions for future rotors. Nor did I want to have to deal with a machine shop to do the work. Similarly I didnt want to rely on RCR for getting rotors, and then wondering if they were done correctly (which 6 of my 8 rotors, including 1 set of replacements, have NOT been correct.)
So, we have arrived at my ultimate solution... I contacted GiroDisc, an American company who make premium two piece floating rotors for everything from Ferrari to Chevy's. I originally asked them about drilling out one of their off the shelf Camaro rotors for me, so in the future when I needed new rotors I could simply swap the outer disk with an off the shelf Camaro SS rotor. They were willing to accommodate me, but they also said if I could get 4 other people together for a group buy, they could custom make the inner portion (called the hat) so that there didnt need to be 10 lug holes, only 5. Within a few hours and a few phone calls, I got the minimum 5 sets to put things in motion. Girodisk tells me that it'll cost $1300 per axle for the custom hats and off the shelf SS rotors, a direct bolt on for any GTR or SLC owner utilizing the Camaro SS brakes and corvette hubs (which is most.). This requires no modification, just remove old rotors and install new.
They last twice as long as standard rotors. Run cooler. Weigh almost 6 lbs less per rotor. Look better behind the wheels.... and most importantly, they streamline future replacement which are much cheaper.
If anyone is interested in joining the group buy or would like more info, please dont hesitate to reply to this post or send me a direct message. I'm also happy to hop on the phone for a call.
If at least one person at some point finds this helpful, then I've accomplished my mission. Thanks for reading!
-Jon
Edit to add: If you're curious if these will fit your car, here are the correct measurements:
Front: 355x32mm
Rear: 365x28mm
Inner Bore: 70mm - 71mm
Stud Hole Needed: 14mm
Most, but not all, GTR and SLC's utilize a C4/C5 corvette hub with studs, but the brake calipers and rotors come from a 5'th generation Camaro SS (2010-2015.). So why cant you take an off the shelf Camaro SS rotor and slap it on our cars? Well, the center hole of the rotor (or hub bore) for the Camaro won't fit the larger corvette hub that our cars use. The Camaro rotor center hole is 66.9mm, and we need the corvette size of 70.5mm so the disc can slide all the way against the hub. So... some guys will just get Camaro rotors and have the center machined out to accommodate our larger hub size.
The next problem; Although the Camaro and corvette have the exact same bolt pattern, the corvette utilizes a 12mm stud and the Camaro a 14mm stud. I've been told the industry standard is to machine the stud holes in the rotor 2mm more than needed so that the studs have 1mm of clearance on all sides when installed. In race applications, the holes are only drilled 1mm larger than needed in order to minimize movement. The concern then is that our studs are only 12mm wide, and they're going into stock Camaro drilled holes on the rotor, which are 16mm (meant for a 14mm stud). While this might not sounds like a crazy amount of slop, I'm told this is VERY unsafe. A hard slam on the brakes can cause the rotor to stop moving while the hub and studs are still in motion due to the excessive play in the 16mm holes. Over time this could weaken or sheer the studs as they aren't made to take that kind of sheering force.
The RCR solution is to take a stock Camaro SS rotor, enlarge the center hole to match what will fit our hubs, then drill an additional set of 5 holes on the rotor to match our smaller studs. In my case, and apparently a few others, the second set of drilled holes were either the larger 16mm size and not the needed 14mm set - or - some of the new holes weren't clocked correctly, creating weak points.
I plan on owning my car for a LONG time, and didn't want to rely on my memory for dimensions for future rotors. Nor did I want to have to deal with a machine shop to do the work. Similarly I didnt want to rely on RCR for getting rotors, and then wondering if they were done correctly (which 6 of my 8 rotors, including 1 set of replacements, have NOT been correct.)
So, we have arrived at my ultimate solution... I contacted GiroDisc, an American company who make premium two piece floating rotors for everything from Ferrari to Chevy's. I originally asked them about drilling out one of their off the shelf Camaro rotors for me, so in the future when I needed new rotors I could simply swap the outer disk with an off the shelf Camaro SS rotor. They were willing to accommodate me, but they also said if I could get 4 other people together for a group buy, they could custom make the inner portion (called the hat) so that there didnt need to be 10 lug holes, only 5. Within a few hours and a few phone calls, I got the minimum 5 sets to put things in motion. Girodisk tells me that it'll cost $1300 per axle for the custom hats and off the shelf SS rotors, a direct bolt on for any GTR or SLC owner utilizing the Camaro SS brakes and corvette hubs (which is most.). This requires no modification, just remove old rotors and install new.
They last twice as long as standard rotors. Run cooler. Weigh almost 6 lbs less per rotor. Look better behind the wheels.... and most importantly, they streamline future replacement which are much cheaper.
If anyone is interested in joining the group buy or would like more info, please dont hesitate to reply to this post or send me a direct message. I'm also happy to hop on the phone for a call.
If at least one person at some point finds this helpful, then I've accomplished my mission. Thanks for reading!
-Jon
Edit to add: If you're curious if these will fit your car, here are the correct measurements:
Front: 355x32mm
Rear: 365x28mm
Inner Bore: 70mm - 71mm
Stud Hole Needed: 14mm
Last edited:
