ABS Failure on the track - root cause
05-06-2009, 11:16 PM
#16
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Was this going into Turn 3? If so, the issue is that the big bump before turn 3 confuses the ABS when the car gets airborne or unweighted. THe ABS system defaults to "No Brakes" and the pedal goes to the floor. If this is the case, we talked extensively about this in the yellow classroom.
That's why some tap the brakes before the bump then trail the brakes into the apex after the bump.
If it's not turn 3, then where?
That's why some tap the brakes before the bump then trail the brakes into the apex after the bump.
If it's not turn 3, then where?
05-06-2009, 11:41 PM
#17
I had this with my M3 when I ran the stock ABS. In my case the problem was caused by trail braking.
When I trail braked into a tight corner hard enough, the car lifts the inside wheel. Because the inside wheel is in the air, the trail braking stops the lifted wheel from turning. Since the wheel is not turning, the ABS system kicks in.
The trail braking in turn 9 at Mosport would freak out the ABS 50% if the time so when I brake again for turn 10, sometimes I would get a hard pedal and other times a soft pedal.
The problem was mostly with the sticky Michelin PSC tires. They were so much stickier then the Toyo RA1s I had before that the chassis would flex that much more and lift the wheel. I went back to the Toyos and the problem went away. The Toyos will drift enough to keep the wheel on the ground.
The real solution was to find a way to keep the tire on the ground or not to trail brake there. If the tire is rolling, the ABS is happy. Ultimately I got rid of the ABS. It never really worked properly on the track.
When I trail braked into a tight corner hard enough, the car lifts the inside wheel. Because the inside wheel is in the air, the trail braking stops the lifted wheel from turning. Since the wheel is not turning, the ABS system kicks in.
The trail braking in turn 9 at Mosport would freak out the ABS 50% if the time so when I brake again for turn 10, sometimes I would get a hard pedal and other times a soft pedal.
The problem was mostly with the sticky Michelin PSC tires. They were so much stickier then the Toyo RA1s I had before that the chassis would flex that much more and lift the wheel. I went back to the Toyos and the problem went away. The Toyos will drift enough to keep the wheel on the ground.
The real solution was to find a way to keep the tire on the ground or not to trail brake there. If the tire is rolling, the ABS is happy. Ultimately I got rid of the ABS. It never really worked properly on the track.
05-06-2009, 11:46 PM
#18
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ABS failure should not reduce braking power it just will go to lockup which is not as effective during a turn. I am not sure I really want ABS to begin with but don't have an option not to.
05-06-2009, 11:46 PM
#19
Rennlist Member
Was this going into Turn 3? If so, the issue is that the big bump before turn 3 confuses the ABS when the car gets airborne or unweighted. THe ABS system defaults to "No Brakes" and the pedal goes to the floor. If this is the case, we talked extensively about this in the yellow classroom.
That's why some tap the brakes before the bump then trail the brakes into the apex after the bump.
If it's not turn 3, then where?
That's why some tap the brakes before the bump then trail the brakes into the apex after the bump.
If it's not turn 3, then where?
Bill, IIRC, he had this problem at MSR Cresson a few weeks back. He was not at TWS with us this past weekend.
Peter...I track a 1997 M3. I have never lifted a wheel trailbraking, nor ever had any ABS problems when trailbraking, even when using super-sticky Hankook Z214's. In fact, I am not in the ABS all that much, and usually only when I get on the pedal a bit too hard initially and/or I don't have my suspension set just rigt for hard braking.
Professional Racing and Driving Coach
05-06-2009, 11:59 PM
#20
In my case it was not ABS failure, but the ABS was kicking in and messing up the pedal feel. It's hard to drive fast when the pedal feel keeps changing.
I am an instructor with BMW and the car was substantially modified. It was also a 97 M3 and had coil-overs, and big sway bars, lots of camber, Euro 3.2L, etc.
All was well with the Toyos. Then when I tried stickier tires, the whole system was thrown out of whack. The tires were so sticky and the suspension so stiff, that the car would lift a wheel all over the place. Imagine heading down corner 2 at Mosport with a wheel in the air. You could hear the chassis creaking like an old barn door - over the noise of the engine and through the helmet. The chassis on an E36 is about as stiff as a block of cheese.
Switching back to the Toyos was enough to make the system harmonious again. It was a really good illustration of how the whole car works as a system. One small change like tires was enough to throw the whole system off.
Since then I have changed to Tilton pedals, dipped it in acid, deleted 1000lbs, and won the Championship. I do miss it as a street car. It was a serious sleeper...
Strip-n-dip photos here: http://www.driversmeeting.com/pcarroll/albums/10
I am an instructor with BMW and the car was substantially modified. It was also a 97 M3 and had coil-overs, and big sway bars, lots of camber, Euro 3.2L, etc.
All was well with the Toyos. Then when I tried stickier tires, the whole system was thrown out of whack. The tires were so sticky and the suspension so stiff, that the car would lift a wheel all over the place. Imagine heading down corner 2 at Mosport with a wheel in the air. You could hear the chassis creaking like an old barn door - over the noise of the engine and through the helmet. The chassis on an E36 is about as stiff as a block of cheese.
Switching back to the Toyos was enough to make the system harmonious again. It was a really good illustration of how the whole car works as a system. One small change like tires was enough to throw the whole system off.
Since then I have changed to Tilton pedals, dipped it in acid, deleted 1000lbs, and won the Championship. I do miss it as a street car. It was a serious sleeper...
Strip-n-dip photos here: http://www.driversmeeting.com/pcarroll/albums/10
05-07-2009, 12:08 AM
#21
Rennlist Member
It's well known that the street ABS system on 911s and boxters/Caymans does not work on the racetrack. It got so dangerous that Grand-Am allowed the koni challenge 911s (street cars, not cup cars) to use aftermarket ABS controllers. Even PCA allows it in stock class. I hope someone comes out with an affordable upgrade for this soon as the Porsche motorsports controller is 5 figures.
05-07-2009, 12:59 AM
#22
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05-07-2009, 02:13 AM
#23
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The scene of the crime was T6 in the 3.1 mile configuration. Here are the skid marks from a video frame taken the next day... I'm glad I decided to start the weekend on street tires; those could have been some expensive skid marks.
05-07-2009, 08:09 AM
#25
Nordschleife Master
The Porsche ABS system has several inputs that do the following:
4 Wheel speed inputs - provide individual wheel speed values
Terminal 61 - This is the Alternator excite wire so the ABS system knows when the engine is running
Brake light switch - This to so the ABS system knows that the brakes have been applied
Power - Powers the system
Ground - Powers the system
I can see that if a brake light bulb shorted the brake light circuit and it blew the fuse the ABS system would no longer function properly. I cannot remember, but I think the ABS light comes on when any of the above inputs are in failure.
A 3 channel street system will always be a problem when one of the rear wheels locks because both rears will pulse. These systems don't allow for agressive braking on the ABS. The 4 channel systems are much better, although they aren't designed for a racing environment and therefore are slow pulsing and don't work well with full slick tires.
4 Wheel speed inputs - provide individual wheel speed values
Terminal 61 - This is the Alternator excite wire so the ABS system knows when the engine is running
Brake light switch - This to so the ABS system knows that the brakes have been applied
Power - Powers the system
Ground - Powers the system
I can see that if a brake light bulb shorted the brake light circuit and it blew the fuse the ABS system would no longer function properly. I cannot remember, but I think the ABS light comes on when any of the above inputs are in failure.
A 3 channel street system will always be a problem when one of the rear wheels locks because both rears will pulse. These systems don't allow for agressive braking on the ABS. The 4 channel systems are much better, although they aren't designed for a racing environment and therefore are slow pulsing and don't work well with full slick tires.
05-07-2009, 08:10 AM
#26
Nordschleife Master
Even PCA allows it in stock class.
05-07-2009, 09:06 AM
#27
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Trying to work on something there for ya...
05-07-2009, 09:23 AM
#28
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In my case it was not ABS failure, but the ABS was kicking in and messing up the pedal feel. It's hard to drive fast when the pedal feel keeps changing.
I am an instructor with BMW and the car was substantially modified. It was also a 97 M3 and had coil-overs, and big sway bars, lots of camber, Euro 3.2L, etc.
All was well with the Toyos. Then when I tried stickier tires, the whole system was thrown out of whack. The tires were so sticky and the suspension so stiff, that the car would lift a wheel all over the place. Imagine heading down corner 2 at Mosport with a wheel in the air. You could hear the chassis creaking like an old barn door - over the noise of the engine and through the helmet. The chassis on an E36 is about as stiff as a block of cheese.
Switching back to the Toyos was enough to make the system harmonious again. It was a really good illustration of how the whole car works as a system. One small change like tires was enough to throw the whole system off.
Since then I have changed to Tilton pedals, dipped it in acid, deleted 1000lbs, and won the Championship. I do miss it as a street car. It was a serious sleeper...
Strip-n-dip photos here: http://www.driversmeeting.com/pcarroll/albums/10
I am an instructor with BMW and the car was substantially modified. It was also a 97 M3 and had coil-overs, and big sway bars, lots of camber, Euro 3.2L, etc.
All was well with the Toyos. Then when I tried stickier tires, the whole system was thrown out of whack. The tires were so sticky and the suspension so stiff, that the car would lift a wheel all over the place. Imagine heading down corner 2 at Mosport with a wheel in the air. You could hear the chassis creaking like an old barn door - over the noise of the engine and through the helmet. The chassis on an E36 is about as stiff as a block of cheese.
Switching back to the Toyos was enough to make the system harmonious again. It was a really good illustration of how the whole car works as a system. One small change like tires was enough to throw the whole system off.
Since then I have changed to Tilton pedals, dipped it in acid, deleted 1000lbs, and won the Championship. I do miss it as a street car. It was a serious sleeper...
Strip-n-dip photos here: http://www.driversmeeting.com/pcarroll/albums/10
Hmm. Interesting. Mine will occasionally lift a tire in a couple of fast on-camber corners at one particular track I use, but only under throttle. Never under brakes. I have Moton CS and 800/900 lb springs (or is it 900/1000? I forget), as well as chassis & rear subframe reinforcements. Car is pretty stiff, although it would be stiffer yet when I yank the 4 point roll bar for a full welded in cage.
So I am not disputing your story, just saying that I have never experienced the same in a similar car, regardless of tires.
Professional Racing and Driving Coach
05-07-2009, 09:48 AM
#29
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It took a while for me to get used to the flashing lights in front of me while pushing myself pretty hard on the track - another lesson in how far behind DE'er skills are to the pros who are processing multiple indicators while going wheel to wheel, driving at the limit, and cracking jokes over the radio, all at the same time.
At least I'm somewhere between that, and the cell-phone wielding soccer mom in a hummer running a red light on under-inflated tires.
05-07-2009, 10:33 AM
#30
Hmm. Interesting. Mine will occasionally lift a tire in a couple of fast on-camber corners at one particular track I use, but only under throttle. Never under brakes. I have Moton CS and 800/900 lb springs (or is it 900/1000? I forget), as well as chassis & rear subframe reinforcements. Car is pretty stiff, although it would be stiffer yet when I yank the 4 point roll bar for a full welded in cage.
So I am not disputing your story, just saying that I have never experienced the same in a similar car, regardless of tires.
So I am not disputing your story, just saying that I have never experienced the same in a similar car, regardless of tires.
As for the ABS problem, I believe on the Porsche you can just pull the fuse and live happily ever after. I don't use ABS on the track any more and I don't miss it. If you can pull the fuse, you can also install a switch and just turn it off.
A good friend of mine drove a brand new 996 into a concrete wall at 160kph (perpendicular) and lived to tell about it. He was relying on ABS when it failed. With stories like this, I prefer not to have it. ABS is meant to prevent ****ty drivers from killing themselves. We're supposed to know how to drive.