E36S50

Are most Porsche racers running with the ABS system on or off?

On the 944 turbo the ABS system is quite old fashion and seems to come on far too early (using race tires) and the pulsing rate is very slow. I am sure the situation is no better on 964s and probably even 993s. No doubt the latest cars (GT3RS, Cup cars, etc) have ABS system designed for high G braking with high Cf pads and R compound tires and can also pulse/cycle much faster than the 15 year old technology on some Porsches.

Assuming an excellent driver is behind the wheel do you not think braking performance and distances would be imporved by disabling the ABS on the older cars?

Thoughts?

FixedWing

I understand the new 997 GT3 Cup does not have ABS.

I have heard that only the very best drivers can match even a basic ABS system in the dry. In the wet it is no contest.

I recognise the 996 GT3 Cup in your avitar. Is it yours?

Stephen

E36S50

Interesting. If true was there a reason given for leaving ABS off the spec sheet?

I think we have all "heard" this over the years but I have yet to see any proof. When ABS was first introduced into the mainstream auto makers assured us that it would take a trained professional to match the stopping distance of an ABS-equipped car. However, we have to assume (hope) that most Club Racer types are excellent drivers and that the changes we make to the cars (suspension, pads, tires, aero, etc) might make it possible to improve braking performance by disabling the ABS system.

Anther selling point of ABS was that it is fool proof in a panic situation where the average Joe Blow would mash his foot to the floor and lock up the tires...while chatting on his cell phone One would expect that during any track driving situation one's full attention is focused on driving and "panic stops" won't be in the cards.

Unfortunately not.

clubrcr

I have had the opportunity to get some personal driving instruction from a couple of Porsche factory drivers. During one of my stints, I asked about ABS. The reply was simple...you can steer your car while the ABS is working and you can't while the tires are locked up. I went on to question the reason why so many drivers professional hated ABS when it was first introduced and why Porsche put an ABS switch in the early cup cars. I was told that in the beginning, some of the drivers thought they could control the car better by modulating the brakes. Drivers, once they got use to the ABS wouldn't turn it off. These words are straight from David Murry.

I have raced both with it and wiithout it. I personally like ABS and if given the chance, would always have it.

As far as the new GT3 Cup, I wonderif Porsche is trying to make the Cup applicable to more race venues, you know that some venues don't allow it. Furthermore the GT3R and RS doesn't have it. I assume the RSR doesn't either.

carreracup21

That's what I had heard as the reason they left it off the 997 Cup also. I try never to get into the ABS in my car. As soon as it engages, you can feel the decel rate decrease. I have a switch to turn it off, but I still leave it on. It's better than flatspotting a tire. I imagine the newer ABS units are better though. Supposedly, the 964 Cup ABS also has a defeat mechanism in place that allows you to go full lock with maximum brake pressure, but I've never got mine to do that. In a spin, ABS is often not a good thing.

JackOlsen

If those improvements improve a driver's ability to modulate brakes and stop quickly, wouldn't they do the same for the ABS system?

Brian P

A long time I ago I saw something on discovery channel (or something similar) about how race car simulations compare against actual race car drivers. They had some computer progam calculate what the best time was around a track and then they put some pro driver in to actually drive the track. Of course, the pro driver did better than the best "theoretical" time. However, what was interesting was that the computer gained time in some of the hard braking sections by using ABS. The pro driver then tried using ABS in those sections and improved on his time and beat the best theoretical time by even more.

From my faint recollection of the program, he also seemed surprised by how well ABS worked. To be fair, the show was using regular street cars rather than porsches, so the driver might not have had much faith in the ABS systems of those cars. I've got to believe the ABS system in the Porsche is even better.

With all this being said, I too often like to avoid ABS. It has nothing to do with improving my braking speed - instead, I like to have the car smoothly balanced while I'm braking. I don't like the constant jolts that I get from the ABS. Also, if I'm engaging ABS, I know that I'm leaving braking until the last possible second. Generally, when I do that, it also means that I'll be overbraking the corner.

Larry Herman

I agree about getting less braking once you get into the ABS. That is exactly what happens in my GT3. You can brake hard till you feel the ABS pulse once or twice...that's it. You just cannot stomp on the brakes with reckless abandon; your stopping distances will definitely be longer. I do, however, like the fact that you don't flatspot $325 tires.

E36S50

I am not sure. Let me try to explain one of my thoughts...

Take for example what I will call the ABS lock-threshold. This is how close to tire lock-up the ABS will allow the brakes to go. Assume the factory tunes the ABS to allow the brakes to apply full force for .01sec between pulsations at full ABS activation/braking potential. At this timing a stock street tire will generate it's maximum braking force. When we install a set of sticky tires, perhaps more braking force can be generated by allowing the brakes to apply full force for .02sec between pulsations. The tires is allowed to get closer to locking up and we are able to slow the car faster.

I know for a fact that the '90s generation BMW Grp. N race cars had different tuning/programming for the ABS unit. I don't know for a fact what the change was but obviously BMW found an advantage in braking performance by reprogramming the ABS vs. their street car settings. My guess is that a GT3RS will allow the tires to get much closer to locking under full braking than a Cayenne S will. Why, I don't know, but I think it has to do with slowing the car more effectively closer to lock up but that makes the car more difficult to drive since turning and braking at the same time can't be done as mindlessly.

It is late at night so my ramble might not makes sense

Geoffrey

I believe the newer cup cars don't have ABS because they have adjustable bias control, the same as the GT3R,RS,RSR.

924RACR

No, in fact they'd be likely worsening the ability of the ABS system to control. The ABS on a street passenger car (factory racecars are another story) is tuned for performance of the setup as the car rolled off the line. Changing all those things impacts chassis dynamics and response of the brake system - different weight transfer due to suspension tuning, different wheel inertias. The biggest change other than springs is definitely race tire slip characteristics, as race tires operate best at rather different slip angles and targets than street tires. This will be one of the biggest complaints with having ABS on a converted street car - not being able to get the most out of the tires. From what I've heard, the ABS systems on factory race cars like the Cup cars are calibrated for race tires, etc.

The driver is able to adapt to all of those changes every time he gets behind the wheel. The ABS may not be able to take such huge changes into account. Age of the ABS algorithm also plays into things here, as noted - the 951 ABS is rather old, and would probably drive me nuts on track if I had it (given my experience with the latest in ABS systems); the 993 or 996 would likely be a bit more tolerant, more refined, and less aggravating. YMMV!

(FWIW, I work on ABS, TCS, and ESC systems for Bosch)

HTH...

FixedWing

I brake the same way as you -- using the ABS as a "feeler" and I also get the same feeling that the braking is not as good when the car is in full-ABS. But I wonder if this is psychological and not reality based? To get full ABS you are stomping on the peddle as hard as you can yet the car continues forward and the peddle doesn't modulate anything. In theory at least, having each of the tyres at its ABS slip threshold should produce shorter stopping distances. In an emergency, when I'm looking for the absolute shortest stopping distance in a straight line, I will use full ABS.

The reason I use it as a feeler is because I believe I have better directional control. I will allow the ABS to work on one or two wheels while braking in a straight line but as soon as I want to turn in I will make sure that the ABS is no longer working. If I try to stay in the ABS it will turn in but not as well and I'm more concerned about losing control. In an emergency, in a straight line, I might see the front bopping up and down too much with full ABS which breaks traction.

My Turbo had both steel rotors and ceramic rotors and with the ceramics there was no question that the ABS was being more aggressive. The car had less directional stability and seemed to be allowing greater slip angles on the tyres. I liked it!

Stephen

Larry Herman

I probably should do some tests to compare stopping distances between "ABS threshold" and full ABS mode. I do know, via clenched sphincter experience, that on the track if I am at the limit of braking, and the ABS is triggered by a bump, rough pavement or too much pedal pressure, I am in trouble. I will definitely lose braking effect and be going too fast at my turn-in point. I have even tried increasing the pedal pressure once the ABS is triggered to try and maximize it's effect. My best option has been to pump the pedal once in order to "reset" the ABS and try to re-establish regular braking. Keep in mind that this is only for dry track conditions. I haven't run the car on the track in the wet...yet.

FixedWing

I've had similar experiences. You never really realise how close you are to the limit until you ask for a little bit more.

Interesting you mention triggering ABS over bumps. What I theorise is happening is that when the car hits a bump and gets airborne the ABS kicks in and reduces braking. The front starts to unload and move upwards. Eventually the upward movement stops and the action is reversed. The car lands and the braking force goes up as the front loads again. The front dives compressing the springs. Now we've got a nice little porpoise action going. During the period that the front is unloaded we aren’t going to get enough braking. This isn’t going to be countered by the additional braking we get when the nose dives. The result is longer braking distances and unpleasant feedback. I would guess coming off the ABS stops the cyclical braking and therefore the rhythm which allows the front to settle down again.

Stephen

E36S50

924RACR, thank you for stepping in here and reiterating exactly what I had thought for years. When my car is equipped with sticky tires and race pads I know that when the ABS kicks in (straight line braking on a smooth surface) that the tires haven't reached 100% of their traction potential and I would guess that in some cases as much as 10-15% of the tires braking potential is being wasted.

Short of locating a "race" tuned ABS program for one's vehicle the only option I see to get better braking performance is to disable the ABS.

I am anxious to do some back to back testing of lap times with and without ABS, but track season is still 3 months away