GiroDisc Z28 Iron Conversion Rotors on SS

[CamaroCracka]

I picked up some GiroDisc Z28 Iron Conversion rotors (394mm) and this thread shows what I found.

Warning: I'm too lazy to put these pics on a image site so they can be woven in with the text and there is a fair amount of text. Your going to have to read the explanation of the pic and then scroll down to it, so if you are not interested in nerding out on factory pieces that will get you big brakes on a GenV, you may want to stop here.

I should start by saying last year I bought some Gen6 ZLE calipers and due to Z28 hats being impossible to find, had to figure out a rotor/hat combination that would work. I got some ZLE rotors on a pretty good deal thinking they would just bolt on, but the offset of the ZLE hat is different than a Gen5 leaving the rotor pushed 10mm too far inboard.

My backup plan was if the ZLE hats did not work, I would just use the Gen5 ZL1 hats assuming the Gen5 ZL1 hat was the same size as the Z28 and ZLE hats. However, that is not the case and the Gen5 ZL1 hat is larger in diameter than the Z28 and ZLE hats. The Z28 and ZLE having the smaller diameter hat is what allows for such a wide pad and gives it that huge swept area. I have never laid hands on a Z28 hat, but I believe the only difference between the Z28 and ZLE hat is that 10mm offset difference. The reason I say that is because put on a set of GiroDisc Z28 Iron Conversion rotors today and the offset was perfect for a 2010 SS as one might expect.

Given I had some rotors I could not use and a lack of $1400 for the GiroDiscs, I looked for a hat that would work and took a gamble on some ZR1 hats for carbon rotors. The offset turned out to be correct, but I did have to drill out the stud holes because the ZR1 used 12mm studs. This has worked fine since I did it and there are no signs of abnormal wear, stress or vibration. However, as you can see in the fifth picture down, the bobbin sticks out from the hat 1mm, so you are not quite getting full engagement between the bobbin and the hat.

The first two pics are side by sides of the GiroDisc Z28 Iron Conversion rotors and my hybrid ZR1/ZLE rotor. The next two pics show the diameters of the hubs on the two rotors.

The hybrid rotor did not worry me for street driving, and it might work fine on the track too. However, I am doing the 24hrs course in Dayton in October and I am not willing to take that kind of risk with other drivers at 150mph. Thus, the move to the GiroDisc.

Now for the disappointing part: Because the GiroDisc uses a larger hat, it cannot use Z28/ZLE size pads. It uses Gen5 ZL1 size pads. This can be seen in the 6th pic with a ZLE pad on the left, Hawks Girodisc pad in the middle (size recommended by GiroDisc), and a Gen5 ZL1 pad on the right. This means significantly less swept area than the ZLE and Z28. I'm just a garage hack, so I am not sure how much is lost with that smaller swept area, but I would think a Z28 driver that tracks a lot might not want to move to a smaller pad.

On the upside, they are iron and replacement rings are about $100 more than OEM/Brembo Gen5 ZL1 rotors, so they are certainly a much lower cost alternative than carbon rotors and the pads are a bit cheaper too. They have significantly more mass than the Gen5 ZL1 rotor and look like they would dissipate heat much better as well. By the feel of it, they are a tad heavier than the ZLE rotor too and I know all that stuff about unsprung weight, but I'm not nearly that good a driver to be concerned with that at this point. They also appear to be made a bit better than the Brembo units, at least to me, with their bobbinless design.

Had I known then what I know now, I would probably have gone with the Vette calipers and GenV ZL1 rotors or just left the vert brakes stock and kept the ZL1 brakes I had on the turbo car. I know some of you are thinking that I made a lot of assumptions in all this, and I did. Nonetheless, I do as much homework as I can, but when I run into dead ends, sometimes I try things. It's how hot rodding has worked from the beginning. The good news for you is I am happy to share my findings so your decisions can be more informed than mine.

The last three pics are of the inside caliper clearance with the GiroDisc rotor (where the 10mm offset difference is a problem), The rotor installed and clearance between the rotor and Hawks pad.

As for the ZLE rings and pads as well as the ZR1 hats I have laying around, I will probably continue to run those on the street and save the GiroDiscs for the track. I finally broke down and got a set of Screaming Chicken bolts and it does not take that much longer to remove the rotor than just the pads.

[ariZona28]

Nice write up. Great info. Looking forward to the results on the Big Track!

[olblue75]

I’m working on this swap as well already have my calipers from a C7/Z07 Vette just need the rotors and pads. So a set of ZLE Pads will work instead of the Giro Disc recommend/modified pad design??

[CamaroCracka]

Originally Posted by olblue75

I’m working on this swap as well already have my calipers from a C7/Z07 Vette just need the rotors and pads. So a set of ZLE Pads will work instead of the Giro Disc recommend/modified pad design??

No, the ZLE pad won't work on the GiroDisc. You have to use a GenV ZL1 pad with the GiroDisc.

You might be able to use the ZLE pads with a Z28 hat and ZLE rotor, assuming the Z28 hats are 2mm larger in diameter than the ZR1 hats. I'm pretty sure the ZR1 and Z28 hats share the same bolt pattern.

I have seen some track guys on other forums say they used a spacer behind the rotor to make other combinations work, but I'm not enough of a brake expert to try that with a ZLE rotor and hat. Seems like it would not be much different than running spacers to push the wheel out, but again, I don't have the experience to say if it's solid engineering. If someone ran that, a 10mm spacer should do the trick and of course, extended wheel studs would be required.