Argonaut

I spent Saturday at Summit Point Shenandoah with TrackDaze.com. Had a great time, 4x30 min sessions. The weather was clear and dry, mid 60s to 70 by the afternoon. Some nice cars: a Radical, SRF Ford, several Vettes, couple Elises, an Exige, only one S197 and an older Mustang.

I had a couple changes to my car, mainly a new set of brakes on the front (get to those in a minute) and some new tires on the rear. The rears are Hoosier scrubs from the Grand Am series, first time I've tried them. I didn't know what air pressure to use nor what to expect from them. Our first session in the morning was cold and the track was "green" (recent rain had removed all the rubber). It was an exercise in oversteer control, woo hoo! The combo of a cold/green track and too high psi led to a really loose rear end. I struggled with it the whole session, never getting comfortable and pulled in frustrated but knowing that things would improve as the track warmed up. Unfortunatly in that first session the older Mustang threw a rod, put a little oil on the track and sat all by his lonesome on the inside of a turn for several laps until our session ended. In the afternoon sessions I lowered the psi in my rears by about 8 pounds and that, combined with the warmer, more rubbered track made a big difference in handling.

Summit Point and Roadkill are associated far too often. In one of the morning sessions an instructor hit a deer, yikes! Car didn't seem to be damaged to bad though.

Ok, onto the Brakes. We talk about it on this forum all the time - the brakes are part of an overall system whose purpose is to slow the car from speed. MC, fluid, calipers, rotors, tires, etc are all part of the system and if any individual piece isn't a team player then the whole system can be compromised. And thus I found out how true this is...

In my case, the part that wasn't a team player was the brake pads. A couple weeks ago I installed a set of AP Racing calipers on the front with 2-piece full floating rotors and CL RC8 pads. This is a brake system designed for competition in the SCCA T1 class and the RC8 pads are Carbon Lorraine's most aggressive racing pad.

So here is what I learned: the brake and pad combo WAY overpowered the Nitto NT01's I was running on the front. Especially in the morning on the cold track. Literally every braking point resulted in lock up and ABS activation. The pads instantly grabbed and the Nitto's didn't have enough "stick" to prevent it. My braking distances were seiously compromised by this. Partly this was my braking style but mostly it was the pads were way more agressive than the tires could handle.

Regarding my braking style - in the past, with the OEM calipers and 'lesser' pads, I approached corners at speed and jammed on the brakes. I didn't really need to think about the pressure I applied to the pedal because generally the ABS wouldn't come on, and when it did...no big deal. But with this new system, using the same style didn't work. The wheels would instantly lock and keep unlock-locking until I released. I thought about all this during lunch and in the afternoon I worked on modulating the pressure, applying much less pressure than I normally do. This improved things but still the pads and the tires didn't play well together.

So I guess the moral of this story is you need to approach modifications (whether its brakes, drive line, etc) with some thought about their effect on the system as a whole. In my case, NT-01s are not racing tires of the caliber of Hoosier, Dunlop, Michelin slicks for which the RC8 pad is designed. They were simply too much for the tires. I think I'm going to get a set of Hawk DTC 60s or maybe the Willwood pads and see if I can find brake nirvana.

Sleeper_08

Thanks for sharing your thoughts and experiences so eloquently.

As you may remember I'm also running the Nitto NT01s and for me the XP10/XP8 combo works fine. I'm getting some ABS kick in but only very moderate and when I was really chasing down one of those Vipers at my last event.

The alternative to changing your pads is to move up to Hoosiers

steelcomp

ABS activation is not necessarily a result of lock-up or skidding. It's a result of wheel decelertion speed exceeding the design parameters in the ABS computer. The ABS computer monitors the wheel speed and using downloaded info, computes deceleration rates based on things like tire size, brake swept area, car weight, etc. The computer calculates at what point the tire's adhesion limit will be exceeded based on algorithms computing G forces. When the computed G force is reached or exceeded, the ABS kicks in and dumps caliper pressure on whatever wheel sees that deceleration rate. Maybe one, maybe all four. As soon as that wheel reaches the desired acceleration rate, the ABS again starts re-applying pressure to the caliper, again monitoring the wheel speed.
When you change things like tire size, car weight, and brake area, you completely confuse the ABS since it's doing it's thinking based on the values of the factory equipment. Your tires and brakes can generate much higher deceleration rates before ever compromising the limit of adhesion, but the computer doesn't know this, and will apply the ABS regardless. Additionally, it can't respond properly because the rates of acceleration are so dramatically different that the loading and unloading of caliper pressure by the computer becomes erratic and just makes things worse. If your big brake system isn't designed to work with your car's ABS you could be worse off than before, with your stock brakes.
This info is all available on StopTech's website. Might be worth some reading.

chrumck

Argonaut, I'd start with replacing the ABS unit with GT500 hydro block and FR500S ECU, then focus on the pads.

Argonaut

Valid points regarding the ABS, which emphasize my point, it is a braking *system* and all the components must work together. But I don't think thats the problem in my case. I point this out in most of my posts and its in my sig as well, my track car is a C5 Vette. When I have info or experiences that are track related in general and not make specific I like to post it here. The system I installed was designed for the car and is being used with great success in the SCCA Touring 1 class (near stock). I'm pretty sure the problem I experienced was the pads overwhelming the available grip of the tires, due both to the track conditions and the tires themselves. Try it out, if you have a set of all season tires and a set of real track pads, try doing some high speed stops and see what happens. They don't play well together and aren't intended to be used together and as a result the stopping distances will be compromised. At any rate, I will find out for sure by swapping in 'lesser' pads. It may be a while but I'll report my findings and let you know the results.

JDWalton

this is why when I see people in brake threads trying to talk someone into the, "most expensive there for the best" systems, I usualy point out that most people looking for slightly better brakes will never use 70% of the capacity of those high end $4000+ brake systems.

I hope you can find your balance on the track man. Whats this system feel like on the street?

Import_Slaya

Great post, Argonaut. I found similar when I was testing EBC Blue pads with street tires. Too much pad grip for too little tire grip makes it tougher to modulate braking. I think with some seat time getting used to the combo at the limit, it could be better managed, but not ideal.

steelcomp

I apologise for not giving you more credit. Not too many people understand how ABS really works. Most think it reacts to a lock-up.
Keep us posted.