Z06Fix

I know this has been talked about before, but I can't seem to find any good threads about it. I'm needing to order track pads here in a couple of weeks. Right now I'm running Carbotech AX6's for autox and street driving. I love the pads. Great initial bite and seem to hold up well for my needs. I run them on the front and rear. Now I'm looking at running the XP10's for track use. The question is should I run them on the front and rear? Or run the XP10's on the front and XP8's on the back. I know alot of guys are running the 8's all the way around and love the setup. I wanting a touch more bite than they offer. I look at the threads about the Wilwoods and most are running the H's on front and rear. Why do most run a step down in the back when running Carbos?

Thanks guys.

Eric

Bill Dearborn

I have done that with PFC and Wilwood pads. I ran 01s in front and 99s in the rear. After a going through a few sets of these I started using 01s front and rear and really didn't notice any difference. This was on an 03Z. I do know that when I went to Wilwoods that I could reduce the chances of the rear rotors cracking through by using H pads in the front and E pads in the rear. However, I did notice a difference in braking when I ran this combo Vs H's front and rear. When you go to the Wilwood web page you can see there is a drastic difference in the capabilities of the two pads. There may not be that much difference between 01 and 99 pads. Same may be true for the two Carbotech pads you mentioned.

Bill

Last C5

I've been running the Carbotech 10s in front and 8s in the rear for quite a while now and it seems to be a good combination.

986_C6

Aardwolf

As far as I know, many run a lesser pad in the rear to prevent the rear locking up before the front. How do people dial in their bias for different situations with an adjustable bias? Perhaps in the wet the same pads front and rear would be poor, skidding the rear a lot. I have planned to try the same pads all around and have not had the chance to as of yet, to see how the car would do.

cj68

FWIW, I was told (by a local instructor who is a forum member) that it decreases the rear end "squirming" under hard braking where you are coming off of a long straight at high speeds. I run XP10s in the front and 8s in the rear and it has gotten rid of the squirming that I would get with stock C5 Z06 pads.

cj

davidfarmer

you would usually do this due to heat ranges. Back in 2002 &2003, I ran Hawk HT14's in the front, and HT12's in the rear. Not because the 14's had more bite, but they were capable of working at 1400deg F, which is the kind of rotor temps we were seeing. In the rear however, we only saw (guessing) 800deg. It was just a matter of running the pads in their appropriate heat ranges.

In their heat ranges, most pads are capable of more or less the same amount of torque, ie enough to lock the tires. Street pads are grippy at ambient temp and up a few hundred degrees, track pads are horrible at low temp (usually), but are amazing at high temp.

Aardwolf

I thought about that with working pad temp. I am thinking of using PFC 97 in the rear, it's one of the few race pads I've seen listed for the C4 rear. Both the 97 and the 01 are listed on the PFC homepage as 167° min. temp, it can't take much to get that low of a temp going.

fatbillybob

I have exactly this problem now on stock pads. This is worth a try. What I don't understand is that our cars in comp mode even have ABS active. ABS is a giant automatic proportioning valve. So in effect you are altering the front rear brake bias by pad switch but because of the ABS you should not need to alter the bias because the ABS will ensure proper non-skid grip. So my question is how does this pad alteration work since ABS is still doing its thing?

fatbillybob

So maybe if you did not know which pads to use from forum member rec you could use tempilac paint to determine rotor temps and chose pads that way to be in the optimum heat range. Or is there more to pad selection than that?

Aardwolf

As far as I know the ABS doesn't do proportioning, that on my year car is done by the spring in the M/C. I put the DRM spring in to have more rear bias. Having a higher torque rear pad seems to change the bias in that you have more stopping power in the rear.

There is less heat generated in the rear because less braking is done there but also on my year car there is less airflow so they would run hotter. The pads that I have looked at as in my above post show 167° min. temp. That is really very little heat, IMO they would be warmed up to temp way before the tires are.

If your rear tires are skidding before the fronts I would change the rear to a lesser torque pad. This is because the front does it better, with weight transfer onto the tires.

I'm always interested in learning more and am curious how bias is adjusted by the driver when an adjustable bias system is used. When is more rear bias used or not used?

mgarfias

THe Z06es use the ABS system to dynamically alter the proportioning.

Aardwolf

Sweet! It's like traction control for the brakes? Can it do per wheel or just per axle? Makes me want a Z06 all the more.

Bill Dearborn

In 2001 all C5s received Dynamic Rear Proportioning as part of an overall ABS system upgrade. That is why there isn't a brake bias spring for them. Here is the description of how it works together with the ABS to control rear brake pressure and yes it appears from the description of the ABS system and DRP that it can control pressure to individual rear wheels.

Antilock Brake System
When wheel slip is detected during a brake application, the ABS enters antilock mode. During antilock braking, hydraulic pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. A separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decrease, hold, or increase hydraulic pressure to each wheel brake. The ABS cannot, however, increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking.

Dynamic Rear Proportioning (DRP)
The dynamic rear proportioning (DRP) is a control system that replaces the hydraulic proportioning function of the mechanical proportioning valve in the base brake system. The DRP control system is part of the operation software in the EBCM. The DRP uses active control with existing ABS in order to regulate the vehicle's rear brake pressure.

Bill

fatbillybob

Yes and this would imply that using different front vs rear pads would not be needed. Yet Cj68 proved that it helpped in his C5Z. I still don't know why unless it has to do with what Dave said about temperatures. Perhaps while the ABS will work regardless of pad...the ABS will work better with more ultimate grip if the pads are temperature matched to the conditions they need. And maybe what Cj and I feel as "loose" is actually the ABS trying to modulate braking too early and inefficently.

bgx12

I am running next week with XP 12 in the front and Xp 10 in the rear. Is that too much brake?

tmak26b

I hope you have some good rubber. I used 10/10 with street tires, I had to be very careful so I dont get into the ABS. I still think the C6 has too much front bias, I am looking to get more brakes in the rear. A check with a infrared gauge showing 5x the temperature in the front vs the rear.

beerkat

Next time I change my pads I will be running Carbotech's XP10 front and rear so I will be you some feed back after NCM/VIR

Solo2GS

I have run that setup for years with race rubber. Great combination!

I even leave them on for the occassional street driving I do in the car between events. No problems...

Bill Hetzel

Most everything I race has dual mastercylinders with adj. bias.
The MC pushrods are connected to a bias bar at the pedals. Inside the bar is a spherical bearing that has a threaded rod thru the center. The rod is connected to each MC pushrod with a clevis and has a cable attached that can spin the rod from a **** on the dash. This moves the spherical bearing left or right to adjust the bias.
The initial setup is to make both MC pushrods the same length (they'te adhustable for lenght), then measure and center the location of the spherical bearing inside the bar.
Initial bias is setup on jack stands by depressing the pedal until the fronts just lock up. This usually takes 2 people to do. The guy rotating the tires should be rotating the tire as the pedal gets depressed until he feels them just lock up. Then he moves to the rear and should be able to just barely rotate the rears with quite a bit of force used.
You then should check the other front and rear to make sure that all calipers are exerting the same force.
Note: If the pads aren't bedded in, this might not work as well as it should. But if you're racing, there should be a couple of sets of bedded pads in the trailer anyway.
After setting the bias in the shop, hit the track, get the brakes and tires warmed up and do a couple of threshold braking runs to see how the bias is working and adjust if necessary. It helps to have someone watch the f & r wheels while doing this.
Do it this way and the driver very seldom needs to adjust the bias in the race, usually only when something startes to go wrong.
If it starts to rain, we usually dial in more rear to keep the front tires from locking up.