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Discussion Starter #1
A question about ABS and brake pedal feel.

Scenario - Was at the last DE of the season. Outside temp around 40 degrees. Was running fairly new R888's, ( about 12-20 minute sessions on them ) along with new pagid yellows, fresh Motul 600, hot tire pressures about 41-43 PSI.

Car was running great, really seemed to like the fresh cool air. I was braking harder and later than normal. Coming off of speeds north of 130mph, under hard braking,I experience the sensation of the brake pedal "pushing" back. It didn't feel like typical ABS kicking in as there was no pulsating or anything.

Thoughts?
 

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Two possibilities in my mind:
1) Proactive ABS, you hit the brakes really hard suddenly and the ABS system bleeds of pressure until you release and try again, or
2) Ice mode.
 

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We used to get it all the time when running a lotus. "Ice mode" usually if the track was bumpy in a braking zone it happened. If you let off and re- apply pressure they would work. Carl
 

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I find Cayman ABS kind of…..for want of a better word…..crunchy. And I avoid it like the plague. It adds tremendous heat to the brakes, and if you stay in ABS you can get Ice Mode and other lumpy push-back/fading and cooked brakes (ask me how I know). I go to that point, then back off a hair. Porsche brakes at that point are very good, and there's nothing to gain from pushing harder.
 

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Could it be brake assist? If the car thinks you're in a panic stop, it applies full braking even if you don't.
 

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ABS provides you with control. It does not shorten the braking distance or make braking more effective. If you are getting ABS to kick in you are overcooking the braking.
 
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Discussion Starter #7
I find Cayman ABS kind of…..for want of a better word…..crunchy. And I avoid it like the plague. It adds tremendous heat to the brakes, and if you stay in ABS you can get Ice Mode and other lumpy push-back/fading and cooked brakes (ask me how I know). I go to that point, then back off a hair. Porsche brakes at that point are very good, and there's nothing to gain from pushing harder.
I was getting what you described as "push back". Never had it before. Only difference this day that is was colder. (started in the 30's), I was going faster, and my tire pressure was higher than normal. It happened three or four times. When it got to that point I simply backed off a bit and re-applied a little lighter. Brakes stilled worked fine. Just a little unnerving. If I understand your experience, you have your car figured out to the point that you can avoid this situation by your braking control?
 

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Try bleeding off some tire pressure next time. 41-43 seems really high. I try to max out at 36 on NT-01s. That could have definitely affected your braking behavior.
 

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If I understand your experience, you have your car figured out to the point that you can avoid this situation by your braking control?
Correct. After a few laps, you should be able to gauge your velocity in each braking instance - and go to that point. If you dip into ABS, just relax a bit....and that's your reference point for braking in that corner.

Oh - and different pads will require different amount of brake pressure. So when you change pads, you'll need to adjust accordingly.
 

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I find Cayman ABS kind of…..for want of a better word…..crunchy.
That describes most ABS systems I'm used to.

I also agree that best braking is by keeping out of ABS. I take ABS activation as a sign I'm doing something wrong (like panicking).
 

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That could be the ABS pushing back on your foot to relieve the pressure on the brake pedal. My thought would be...you pressed too far on the pedal, activating ABS, so for the brakes to stop locking up, you need less pressure. So maybe the car is helping you adjust that pressure by pushing back at your foot, reducing the pressure you are applying.


That would be my guess.

The best braking power comes from just shy of hitting the ABS, so if you feel abs... come off the brakes a little, and I promise, you'll stop faster.
 

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This presentation is fantastic. I saw it live last month at Tech Tactics, put on by PCNA and PCA. Found out all sorts of stuff about brakes that I didn't know.
 
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