After multiple problems with my stock Z51 C6 brakes on the track, I bit the bullet and bought a set of monobloc 6-piston Brembos for the front only. Problem solved.

Yet, given the tiny size of the rear calipers, plus the amazingly small swept area (only about half the rotor is swept by the pad), I am considering adding Brembo 4-piston monoblocs to the rear, in the hopes of gaining more life out of the front Brembo rotors and better balancing the overall braking of the car.

My question is this: since the front/rear biasing, as I understand it, is all electronic, does the car "know" that there is a lot more rear braking to be had with the Brembos and make adjustments for it? If not, is there any way to bypass the computers and add more rear bias to even things out?

Thanks

Terry

 

 

you should be better off with the brembos all around then you are now.

 

The Brembo front kit is designed to maintain similar bias to the OEM calipers/rotors. Adding the rear Brembo kit won't do anything to reduce the wear on the front components.

I should also point out that the biasing is not done electronically. There is a non adjustable proportioning valve that determines the pressure ratio between the front and rear brake systems. Generally, most cars come from the factory with too much front bias(for safety reasons). Going with an adjustable brake proportioning valve would allow you to change the default bias. DRM sells an aftermarket master cylinder with an adjustable proportioning valve. You can find it here: http://dougrippie.com/products/drm-c...ster-cylinder/


To be honest though, I think you should check out this book to get a good feel for how braking systems are designed and why so many people incorrectly assume larger rotors and more caliper pistons result in decreased stopping distances/increased braking force.

 

I have been considering the DRM kit, whether or not I decide to go with the rear Brembos. Clearly, the rears can contribute much more. Back when I was W-T-W racing, I actually liked as much rear bias as possible while still maintaining control.

My goal with the Corvette is to remove brake fade/worries from the equation altogether, since it will be driven by me, my daughter, and my son in some events. I'm thinking the DRM kit and the rear Brembos will achieve this.

 

BTW, I am not one of those who thinks larger rotors and more caliper pistons result in decreased stopping distances/increased braking force. If only it were that simple!

I'm more concerned with balanced wear and economy. I used to run a 944/968 hybrid at three-day events. The front and rear pads were the exact same size, so each evening my buddies and I would stand around and laugh as my little (then) 18-yo daughter changed pads front to rear.

 

Cool!

Sounds like you know your share.

I've spent some time trying to balance the economics equation for various brake setups. Still can't decide if it's cheaper to run 13" or 14" rotors up front. Out of curiosity what car were you running at the 944/968 events? I've been eying 968s for some time but I recently got the 993 bug so I've been shopping for those too.

 

Came in to post that this is actually wrong. The early C5s had proportioning valves. All later C5s and C6s have electronically control brake bias.

 

I had a full race caged 944S2 with a built 968 engine that I ran on both coasts. The summer of 2006 my company got bought and my daughter turned 18, so we took the entire summer and ran 23 days--Watkins Glen, Summit Point, Shenandoah, Mid Ohio, and VIR. Towed 10,000 miles together, and by the end of the summer she was kicking my *** around the Glen. Definitely a cool way to spend a summer.

Can't wait to see what she can do in the Corvette.

 

OK, well then, back to my original question--will the computer "know" there's more braking torque to be had in the rear and adjust accordingly (can't imagine how it could, but I'm of the pre-comuter generation), or do I need to manually override it to get the benefit of more rear torque??

 

This hasn't been true since the 2001 model year. Since then GM has used dynamic rear proportioning (DRP) to affect the basic brake bias built into the system. The basic brake bias is determined by the difference in rotor diameter and piston area of the front brakes Vs the rear brakes. DRP has replaced the bias spring. If you look at the DRM web page you can see their spring only applies to 97 through 00 C5s only. The way I interpret DRP is the EBCM will apply as much brake force as the rear can take without locking the rear wheels or up to the limit of its capability to pressurize the rear brakes.

Swept area doesn't really change the bias as the pressure applied by the pistons is applied across a larger area. Thus the pressure/area reduces and you get the same braking force as you would with a smaller pad.

An aftermarket package from Brembo/Stoptech/Wilwood will take rotor diameter and piston area into account so they can maintain the bias between front and rear. If you choose just the front set up and keep the stock rear you could unwittingly change the bias toward the front. Not sure about all of them but I know the Wilwood package uses 14.5 in rotors in the front and 14 inch rotors in the rear. If you install just the front kit you have may have moved toward more forward bias. It all depends on whether the Wilwood caliper has the same, less or more piston area than the stock caliper. It it is the same or more you definitely have moved bias to the front and if it is less it depends on how much less.

Bill

 

If the bias is electronic, is there a "learning period"? I just added the Z51 rotors to my car and am temporarily running the base calipers in the rear. In a recent aggressive stop I got the rears to lock for a moment before the ABS kicked in. Proper bias should not trigger ABS on one end of the car on dry pavement (it was not THAT hard of a stop)... Can you have a brake system so poorly matched mechanically that the electronic bias is "overwhelmed", and the ABS has to step in and save the day?

 

What's being changed here with the electronics is the dynamic bias. Knowing the static bias first and comparing that to the proposed change is a good place to start.

Just because the proposed four pot caliper has four pistons rather than one doesn't inherently mean it's better (and not 4x). To compare the information correctly you'll need to know the area of the stock piston relative to area of two (one side) of the new caliper. If the area is more then you'll have more clamp load for the given input pressure and thus more bias to the rear. But if it's too much you'll also have a longer pedal.

Bill's correct that swept area is not a bench mark. Nor is pad size. Larger pads don't make more brake they just last longer. Pressure is what you're looking at. The pad size can however change the effective radius of the torque a small, narrow pad puts the average pressure point higher on the disc for example.

Get the data and I'll be happy to run it for you both before and after the change or you can use the online bias calculator I offer.

As for the prop valve...this stuff is getting really complex. What I'll say tho is that you'd never want to put an adjustable valve in a system where the stock valve is also used. And keep in mind a prop valve does not mean more brake, it's just used to restrict the rear flow at an adjustable pressure (knee) point. (rather than the sock one at a predetermined one or using electronics to gauge it)

 

Thanks for all the great information, gentlemen. I found Bill's comment that I may have moved more bias to the front very intriguing. Also Todd's comment about not adding an adjustable valve in a system that already has a stock valve. Does this mean the computer-driven biasing would have to be dialed out (lobotomized) if I used the DRM setup?

I'm not looking for more braking power--I already have plenty enough to haul the car down from the 150+ it sees at Pacific Raceways in Seattle.

What I want is for brake fade to be a non-issue when my son, my daughter, and then I jump in the car for three successive run groups. I also want more life out of rotors and pads.

I am heavily leaning toward just adding the matching Brembo to the rear and trusting to their engineers that they have thought about these issues.

 

So the question remains... How much can the electronic bias valve compensate for mismatched components? In other words, is it an active system, where it does the brunt of the work, or is it simply there to fine tune an already well matched brake system?

 

Curious to hear also. Someone with inside info to the computer program would be the only person who probably knows. And I suspect it's not shared...