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I had a very informative discussion with an engineer at PFC regarding ABS and braking techniques for the 997.1 GT3 RS. I'm not sure which other models this might apply to, but I thought that it was pretty valuable stuff. Especially because I can show that it works (see figure below).
He told me that if the vehicle senses that you went from throttle to max brake pressure in some very short time (i.e., a second or so), then it assumes that you are braking to avoid hitting something that popped up in front of you. If the ABS has not been reprogrammed, then for this case, the ABS will come on and hold the car at max deceleration of 0.9-0.95g. This is true even if TC is OFF, which is how I drive on track. That is the limit for street tires. My track data always showed me braking at this limit, even though I have Nittos that will hold 1.2g in turns.
He also gave me a technique to get around the ABS intervention. If you roll smoothly and slowly into the brake, and then get hard on them, the ABS will not jump into panic mode. Instead, it will go back to sensing lockup. This really works! Look at the friction circle plots below. On the left is my best lap from Road America last year, and on the right from this past weekend. Everything on the car is the same, even the tires, although they now have an additional 25 heat cycles compared to last year. Weather was the same too. You can see that I am now hitting 1.2g under braking. I've also been working on trail braking, and you can see that I am getting better at it. Also, a couple of times I reverted to the immediate hard application, and I could feel the ABS taking over and limiting the braking. This technique seemed to be good for 1-2 tenths per corner. That's nearly a second per lap at RA just from better braking technique.
-- Jon
Friction circles at Road America. Left: 2013, Right: 2014. Car and conditions are as close to identical as possible
This is great! and you're right, the top left and right quadrants of the circle are getting much more dense. And I've always heard that the transition to brakes and off of them should be smooth, you just gave me a bunch of reasons to try it!
When you feel ABS become active do you hold pressure? A lot of drivers once they've felt the pedal start moving from ABS will stop increasing brake pressure assuming there's no more left. In the case where panic braking has been detected it will tend to force the car into ABS, but you should still be able to press the pedal harder. I suspect that if you push thru it your braking data will look the same. For a panic brake event, the brakes are applied to reach a certain deceleration rate, but it will allow more deceleration if it is available and the driver is pressing hard enough.
When you feel ABS become active do you hold pressure? A lot of drivers once they've felt the pedal start moving from ABS will stop increasing brake pressure assuming there's no more left. In the case where panic braking has been detected it will tend to force the car into ABS, but you should still be able to press the pedal harder. I suspect that if you push thru it your braking data will look the same. For a panic brake event, the brakes are applied to reach a certain deceleration rate, but it will allow more deceleration if it is available and the driver is pressing hard enough.
What I felt when the ABS was taking over was just a really hard pedal, and increasing pressure did not make any difference. It's a bad feeling - like there isn't nearly enough braking - so I was definitely pressing harder looking for more.
What I felt when the ABS was taking over was just a really hard pedal, and increasing pressure did not make any difference. It's a bad feeling - like there isn't nearly enough braking - so I was definitely pressing harder looking for more.
Ice mode.
I'm now using your same technique although my charts don't look as clean as yours yet. Jab pedal, ice mode. Smooth pedal, stop like crazy.
I'm now using your same technique although my charts don't look as clean as yours yet. Jab pedal, ice mode. Smooth pedal, stop like crazy.
I wondered if that was the infamous "ice mode." Thanks for clarifying. You're still slowing, but with about 20% less efficiency than you were expecting.
Oh, and not all of my charts look that clean. I showed you a good one (from my best lap)
When you feel ABS become active do you hold pressure? A lot of drivers once they've felt the pedal start moving from ABS will stop increasing brake pressure assuming there's no more left. In the case where panic braking has been detected it will tend to force the car into ABS, but you should still be able to press the pedal harder. I suspect that if you push thru it your braking data will look the same. For a panic brake event, the brakes are applied to reach a certain deceleration rate, but it will allow more deceleration if it is available and the driver is pressing hard enough.
I personally don't believe this from many a track day experience with the 997gt3.mk1 ABS module - I could be wrong but don't think so.
I do agree that the soft then hard then harder is the way to achieve the highest Gs but the issue is the time lost in doing this slower transition is what is frustrating. That is why I think left foot braking might be the answer. I have been experimenting with this technique for about a year now. I start braking with the left foot, then both feet for a moment, then left foot over to clutch for H/T downshift, then left foot back onto brake pedal to finish braking and then pick up the throttle 1/10th earlier as left foot is still on / but coming off brake pedal - go-cart like. Give it a try.
MS ABS is the ultimate answer unfortunately... of course one can "drive around" ice mode (I do) but it sure would be nice to have a bosch ms abs set up
10-01-2014, 03:57 PM
Managing ABS intervention for more braking g's
