EVOVII_SWE

Thanks for the info Jeff.

CentralCoaster

So I take it the GM engineers didn't speak too highly of the padtastic PBR design?

Jeffvette

On the super car, you won't see a PBR setup. I never could get a name out of them, but after seeing some of the shots, I'm suspecting Brembo.

rickneworleansla

Thanks Tom. I'll go back and search for the old post.

Jeff,

Does this seem pretty accurate regarding the different systems on a C4? I have the J55's now. Do you know the actual weight of the different calipers?

Thanks

Tom Piper

I also remember thinking that the total unsprung weight was close to being the same (although the adapters added some weight).
But, since the C5 rotors weighed less, the "flywheel" effect of the rotors was less -- during acceleration less hp to get them moving.

Tom Piper

Jeffvette

Let me go back through my notes. I do know the C6 Z06 caliper weighed the same as the C5 caliper with the abutment bracket.

rickneworleansla

Sorry I was meaning to type rotors. I am more concerned with unsprung rotational weight.

Jeffvette

I've got all that as well. The caliper weight was what stuck out in my mind.

Tom Piper

If you are concerned about rotational mass enertia, I think the diameter of the rotor comes into play there too -- not just the weight.

I think the C5 rotors are 12.8" instead of 13".
So, the mass is not as far from the center which should have an impact too.

Any mechanical engineers with some formulas out there?

Tom Piper

ScaryFast

Moment of inertia equation:

I = mr^2

The moment of inertia equals the mass of the rotating object X the radius (squared). You'd take the center of mass for the rotor and use that for a general answer. The center of mass in a 12.8" disc versus a 13" disc of the same thickness, etc. will be closer to the center. Therfore it will have less rotational mass, and be easier to slow the rotation via the caliper.

However, in a brake rotor, more mass means better cooling and potentially a larger friction surface, so like anything, there is a balance between rotational mass and stopping power. In addition, the rotor is a small part of the rotational mass, don't forget the wheel and tire...

ScaryFast

Jeff, can you please clarify this statement from your earlier post?

If you're saying you have a rear C4 kit available but aren't making more then I might want it - I need to improve my rear brakes. I'm having rear lockup and this is one of the avenues I'm exploring to alleviate the problem. I have a set of the front PBR calipers, and was going to fab up some brackets. But if there's something available it would be easier...

Mojave, have you done anything to your rears?

Thanks guys...

Jeffvette

I have a full rear kit that uses a C6 Z06 rear caliper and a seperate parking brake. This kit is going on the Admiral Blue ZR-1. I won't be using the C6 Z06 gear any more as I'm waiting on the Blue Devil gear.

ScaryFast

What else have you used, anything with the stock C4 front brakes?

Tom Piper

ScaryFast,

Thanks for the answer.

So, the smaller diameter disc (assuming the same mass) would have less moment of inertia and be easier for the calipers to slow the rotation and also easier for the engine to increase the rotation during acceleration.

I know the C5 rotors weigh less than J55 rotors (don't remember how much less). I think C5 rotors are thicker where the pads contact it (should be more mass where it counts), and are smaller in diameter (less moment of enertia).
So, in general, they should be better I would think.

However, it seems to me, the diameter of the J55 rotors being greater would seem to have a mechanical advantage (in other words the pads would have more leaverage with the same bite being farther from center).
So, is there more advantage in stopping power from less moment of inertia of a smaller diameter rotor or more leaverage of a larger rotor?

By the way, going from memory, which becomes less every year, I think the C5 rotor has more mass in the area of pad contact, but less mass overall due to smaller diameter and the C5 rotors are not "dished" inwards from the spindle hub as far -- that's why some wheels won't work because the rotor and caliper are farther outboard due to less "dishing" of the rotor.
So, the C5 rotors have more mass where it counts.

Therefore, if my logic is correct, the C5 rotor has the advantage in every way except for the leaverage of the pads that would be farther from center.



Tom Piper

ScaryFast

Right. Same concept applies to flywheels, etc. It's also why we put weight as low and toward the center of a race car as possible, makes it less likely to spin. The farther weight is from the center the easier it is to spin and the harder it is to stop once it's rotating.

Possible, but I'm going to have to admit ignorance on this one. I guess a brake engineer would have to determine at what point one factor is more of an influence than the other. In this case, at what point is the clamping force of the rotor great enough that it can stop a higher rotating mass...or said the other way, at what point is the additional rotating mass too much for the caliper design?

It's also one of the reasons two piece rotors are popular in performance cars. The hats are generally aluminum and very light. The only heavy steel that is spinning is the area that is directly contacted by the caliper / pad.

Tom Piper

ScaryFast,

Take me one step further.

Point 1:
Going by the previous posts, it would seem that the J55 rotor with a larger diameter, and more mass, would have a moment of enertia that would increase at a greater rate than the C5 rotor as rotor speed increases.
So, it is entirely possible, in fact, likely, that the J55 rotor, because of more leverage, may be a better perforrning rotor at low speed and the C5 rotor may be a better performing rotor at higher speeds.

Point 2:
The aluminum hats of exotic two piece rotors may be good performers, but may not be durable in the long run due to warpage, etc. And, since the hat can be changed, for the track, they can be changed frequently if needed.
However, for a street machine, the C5 rotor lies somewhere between the J55 rotor and the exotic two piece rotor -- so, it is a good compromise for a street machine because it would be more durable than the exotic two piece rotor.

Comments?


Tom Piper

johnnymo63

There are definite advantages to using the C-5 brakes over the C-4 HDs. The size difference of the pads is huge. The C-5 pad has much more contact area and the C-5 pad covers all of the rotor. (C-4 only touches about 2/3s of the rotor surface).

Also, I think the caliper piston diameter on the C-5 is larger. And new C-5 rotors are $30 as compared to close to $100 for the C-4s (HD).
Both the C-5 standard and the C-5 Z06 calipers have "Corvette" cast on the side facing out.(Frt. only). Std. are black and the Z06 are red. (Both already painted).

The rears are usually not used on C-4s because the E-brake is not easily compatible.

Upgrade to hi-performance pads (like Hawk HPS) and braided brake lines, flush system w/ DOT-4 fluid and this should make a heck of a difference in stopping power.(No fade)

Wheels - to run C-5 brakes on a C-4, (88-96) "Sawblades" won't work.(Unless you use a spacer, I think 1/2" for 8.5" and 1/4" for 9.5" wheels). 89-90 17" wheels work as is.(not sure on 88s). "A-molds" or any C-5 or C-6 wheel will work w/o spacers.

EVOVII_SWE

How does the C6 brakes compare to the C5 then?

Mojave

Once again, base C6 and C5 brakes are the same. The top window of the caliper is slightly smaller on a C6, and they don't use the top anti-rattle clip, but the calipers are otherwise the same. They use the same pad bracket, same rotor, same pads, etc, etc.

Z51 C6 use base C6/C5 calipers, but the pad bracket is moved out to accommodate a .5" larger rotor. Z51 C6 use the same pads, slide pins, etc, etc, etc.

I'm not sure why everyone is focusing so much on the weight of the components. Sure, rotating and unsprung mass is bad, but we are talking about street cars here. I doubt anyone will notice the one extra pound of brakes.

EVOVII_SWE

Sorry, I was too focused on the Z06 to even read your first post properly :o

I think I should try to find a C6 brake setup instead