Cossie
I had 2 Rx8s and track them on a regular basis. Galiper would heat up, creating brake fade but the "Z ice mode" is different. I experienced it 2 times at the far end of a long braking zone where i needed extra braking, than "poof" no brakes at all... and the next corner was fine (which shouln'dt be the case if it was heat related). My theory does on ABS sensors recating funny when the rear will do not have enough road contact.
As said before, we may to adjust our driving styles accordingl until a solution is found...
Phil

After re-reading the Car and Driver article I am preparing a test to determine if it is boiling brake fluid that might be confusing the abs system.

On Friday I will be doing a track day at the Summit Point main circuit. Last time I ran Porterfield R4 full race compound with ATE super blue fluid and I experienced ice mode three times. I have made three changes to my brake system.

1. Castrol SRF brake fluid (at $80 per liter).
2. CarboTech XP10 pads up front and XP8 in the rear.
3. Home made brake cooling ducts from the fang inlets (however, they are not directly connected to the inside of the rotor).

I'll let you know how it goes on Saturday.

Looking forward to hearing your results.

That sounds good.

The expensive fluid won't lower temps as you know, but will have a higher b.p. So, you still may have an ABS sensor that gets excessively hot, and as you say, you will only be able to rule out fluid boiling as an individual cause.

Where are you pointing the air if not at the inside of the rotors? How far away is the outlet? Perhaps if you can point them towards the ABS sensor we can test the theory of sensor overheating as a cause.

The other one we need to test is differential wheel spin...

Suscribed

The ducts are pointing (as best I could) to directly under the brake caliper. I connected the end of the tubing to the lower part of the shock absorber. I would guess about 4 to 6 inches from the rotor. The main problem is the shape of our front spindle. It really blocks access to the inside of the rotor. In hindsight, I should have cut off the entire dust shield but I don't have a proper sheet metal shear (and I was getting tired).

I should have taken some pictures but I was not all that anxious to display my ghetto-cooling ducts. And it did take some cutting of the inside fender cover...


Keep in mind that I was retrofitting my fang ram air setup and this limited the length of my brake tubing.

So I finally experienced this at the last event. Last run on the day with a very hot and tired car. Noticed the ABS engage wayyy too early on the second to last corner then coming through the finish had almost no brakes, very strange feeling.

Car has all stock brake components with Hoosier A6's.

^ Sounds like fade? Maybe you glazed the pad?

Sorry to go offtopic folks, but I want to get in on the fun too. Where are you all buying your Carbotech pads at?

Forged gave me a pretty reasonable price.

Same thing happens to me. I thought it was fade at first, but the ABS ends up pulsing the front brakes, not the rear. If the fronts were overheated you would expect the rear brakes to be doing all the work and locking up as a result.

Something is f-d up in the ABS program (of which heat is an apparent factor). I'll know more this weekend after taking some measurements.

ABS systems are supposed to activate when the speed sensor at each corner notices the tire slowing down faster than it is physically possible for the entire car to slow down. When it reaches a threshold, it releases brake pressure to that corner until it senses some acceleration back from that tire, immediately after it lets it decel again until it reaches the threshold and the process starts all over.
I don't think our system is malfunctioning, in fact I think its working too well. It just thinks its going to loose traction immediately after it reapplies pressure. I think the parameters of the ABS system are simply too conservative to be taken on the track, problem is that if they were what we wanted, then we would have inexperienced drivers (read: the same idiots who crash when they turn vdc off) crashing in the rain all the time.

So put yourself in the shoes of the mfg, they would obviously rather a bunch of us enthusiasts bitch that we can't use our cars on the track that well, than people crashing and dying.
It happens to GT3's and Exiges all the same. The only thing we all really have in common is that the ABS system needs to be there to keep people in one piece and needs to undergo rigorous testing to meet standards.

At the same time, I realize that if the system were working properly, it should detect a point in which the tire deceleration can in fact keep up with the car's overall deceleration and stop the ABS system. If the ABS were programmed for big sticky tires such as the ones we have stock, that should minimize the intrusion of the system. It would allow for a more aggressive discrepancy between car decel and tire decel. I think thats too expensive though, to develop a customized ABS system specifically for this car and specifically for us track goers. They would rather probably use the same system as they do in the sentra, maxima and cube. Not to mention the problem again becomes; what happens when that same car is in the hands of soccermom late for practice in the rain?

The only way I can see us getting around this problem is turning abs off or having a system that is designed to allow more aggressive tire compounds. As someone already pointed out, that option is the BMW system that is $15,000.

I wish we had some sort of "Track" button that would switch us to a more aggressive ABS tune. I'm pretty sure Ferrari has such a system implemented within their manetino steering wheel system, but that's why they are $250k.

Anyone ever heard of a way to reprogram your ABS parameters?

In other words, I hope we find something punctual that is specifically causing the ABS to go and remain in icemode, but I have a feeling its just the system doing its job in what it is programed to think is a "complete panic stop". I can guarantee you all that the guys with GT3's out there, who have a little bit more resources than most of us do, (I said most, congrats if that doesn't include you) would have found a fix for this already if it were a hardware malfunction.

Just my .02 and on that note I will also add that I'll be looking for a punctual issue just like you guys. I'm just a little skeptical considering the facts.

EDIT: by this logic...folks with BBK's and stickier tires might be more prone to going into icemode. Maybe we need pads with less initial bite or less brake pressure. I'm just throwing ideas out there that might make someone put two and two together and say "Aha!". Not to mention it should happen less and less and not more and more as our crappy stock pads get hot and begin to fade, but that doesn't seem to be the case either.

Does anyone know what the BMW system replaces? Do they mention any components that hold up better to heat??

Yes I understand the difference between the ice mode and brake fade. At autox, there is no way you can generate enough heat or speed to fade the brakes. What I felt was clearly ice mode where the brakes would just pulsate and not stop. The C6 was notorious for thatThe RX-8 rarely got into ice mode compare to the Z and other cars.

Ice mode is normal as to prevent brakes from constantly locking in the snow

StopTech has a great white paper on BBK's and their potential impact on ABS.

StopTech : Balanced Brake Upgrades

The problems of a misapplication of a BBK described in the article would apply to the braking system across the board however. The issue raised here is after time on the track (heat buildup in the rotor, caliper, pad, fluid, etc.) the ABS system seems to kick in early. The parameters of the ABS system may be so tightly constrained that when brake fade (due to heat buildup) sets in there is an immediate overreaction. When combined with a misapplied BBK, the overreaction is exacerbated.

Possibly. Maybe. Dunno.

It's a possibility. But in this case it would be the stock BBK (small BBK?) that was misapplied. Has anyone with base brakes experienced ice-mode?

I will say that the AP Racing kit goes for a longer period before the heat related ice-mode failure kicks in. The most notable difference besides the calipers is that the rear rotor is much smaller in comparison to stock, reducing the rear bias the stock setup has just slightly.

Hopefully I can get some decent measurements this weekend and we will see just how much heat auto-x can actually generate. Our auto-x courses are roughly twice the standard length, but even still there shouldn't be any way the brakes can overheat in those conditions, but we will see.

I wish we could have real time monitoring of the brake temps. Maybe we could pinpoint a temperature that causes ABS failure.

Who's gonna do it?

http://www.advantagemotorsports.com/Sensors.htm

Last sensor is an IR electronic temp sensor with datalogging.