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I would suggest there is a difference between maximum outright braking force and optimal braking for fastest lap times.
To me, car dynamics are most important if you are after lap times, managing weight carefully to setup the chassis for this and the next turn and hitting your desired line- ABS or at the limit braking can definitely unsettle the car and also rush the driver to the point of making mistakes which lead to slower lap times overall.
It’s nuanced.
I’ve done hot laps with Cass and Hurley at PDE Barber, and also been privy to private instruction at Road Atlanta with David Murry.
In general they advocate brake as late and as hard as you can, NOT breathing slowly into the brakes, especially in a straight line brake zone to maximize speed into the corner - right up to the point where you overcome your ability as a drive to setup the car, downshift (unless your in Auto) and hit your turn in point and become harried. If you’re a pro, you can usually go hard to antilocks and still get it all done - but not necessarily every turn and track on every day as we all know there are important variations (weather, track surface, tire life, other driver’s lines, etc)
Interesting. That was not my experience. I didn’t take the intro class, but I’ve taken all of the advanced Masters RS and RSR classes (multiple times) and they taught to threshold brake and not stay in ABS. They actually have a specific training exercise to engage ABS but then to immediately modulate out of it.
I would suggest there is a difference between maximum outright braking force and optimal braking for fastest lap times.
To me, car dynamics are most important if you are after lap times, managing weight carefully to setup the chassis for this and the next turn and hitting your desired line- ABS or at the limit braking can definitely unsettle the car and also rush the driver to the point of making mistakes which lead to slower lap times overall.
It’s nuanced.
I’ve done hot laps with Cass and Hurley at PDE Barber, and also been privy to private instruction at Road Atlanta with David Murry.
In general they advocate brake as late and as hard as you can, NOT breathing slowly into the brakes, especially in a straight line brake zone to maximize speed into the corner - right up to the point where you overcome your ability as a drive to setup the car, downshift (unless your in Auto) and hit your turn in point and become harried. If you’re a pro, you can usually go hard to antilocks and still get it all done - but not necessarily every turn and track on every day as we all know there are important variations (weather, track surface, tire life, other driver’s lines, etc)
I've always taught students that you want to apply the brakes as quickly as you can without upsetting the car.
I demonstrate it by smacking their upper arm and saying don't do that with the brakes. Then I push their arm quickly and firmly without smacking them and say do that with the brakes. The light bulb goes on every time.
Of course, all of this is when the goal is get near threshold braking. If the goal is lighter maximum braking pressure, the brake application is usually less abrupt - again, to avoid upsetting the car.
Not to brag but for credibility - I race in a very competitive amateur series and can turn in laps within 0.2s/minute of my pro coach, who is an active pro racer with numerous wins. I review data after practically every day of driving and log everything up to the individual wheel and tire temps and corner heights under load, and generally know what each metric means for car setup or driving technique.
Here is a summary of ABS on track based on everything I've learned so far (applies to the 991 or newer GT3 ABS - older ones were not as good).
1. In a straight line and steady state, ABS will stop the car faster than a human, even at threshold-braking. Getting into ABS during straight-line braking will be the most efficient way to brake. It's easy to prove by data. Even if you can perfectly put the pedal pressure at just before the lockup level (most people can't - they just brake too lightly so ABS does not engage), the problem is that grip changes and the balance of grip between axles changes over time, triggering ABS & EBD. So completely avoiding ABS reaction inevitably means that you are leaving braking force on the table. But there is a catch.
2. Engaging ABS has a cost - brake pads can wear faster or even crumble if worn/overheated due to vibration, and can also leave uneven deposits - many have seen multiple overlapping "stamp imprints" of a brake pad on a rotor - that's typically what a result of ABS action with overheated pad looks like. It may cause vibrations and uneven braking in the future.
3. You do not want to engage ABS during weight transfer. For example, if you slam the brakes so quickly the front wheels start to lock up before the weight transfers to them, ABS will engage prematurely and not allow full brake pressure to build up, which will reduce deceleration and delay the weight transfer, creating a kind of a negative feedback loop.
4. Always make sure you are out of ABS sufficiently before the turn-in point. The problem with ABS is that it prevents knowing exactly how far beyond the threshold you are - you could be pushing the pedal 1% stronger than threshold or 50% - it will feel the same. And when you start turning in and gradually releasing the brake, you need to index the brake release from the threshold. Let's say you know you need to be at 60-70% of the threshold the moment you start turning in. If you are in ABS, you will have no idea whether you need to reduce the pressure by 30% or by 60% because you cannot feel how far past the threshold you are pushing into the ABS zone. So it's important to be out of ABS and feeling the brakes before starting to blend braking and turning, and not get into ABS while turning (that usually just does not work well, too long to explain why).
5. Some anomalies of track surface can make ABS suboptimal even in the straight line - typically it happens when one wheel gets very unweighted or in the air, so it does not provide braking force, and that creates a force that rotates the car (on one side two wheels brake but on the otherside only one). ABS/EBD will try to compensate for this force to avoid rotation or spin, but that may be counter to the driver's intention. In such cases I would not go into ABS if possible or turn it off. But if that happens, you will know exactly where it happens - it's noticeable.
So, unless there are special circumstances, I would drive an ABS car like this:
- Quick but gradual brake application, making sure ABS does not engage before the weight transfer completes (it is very quick, though in the 992 generation and especially in the RS)
- During straight-line braking, feel free to (gently) dip into ABS for best performance (unless brakes are starting to get greasy due to pads overheating). If anything, it's a good way to understand where the threshold is - otherwise, how will you know? In non-abs cars, racers slightly lock up wheels during warm-up to know, for example. In ABS cars, you dip into ABS.
- Before turn-in point, make sure to release brakes enough to not be activating ABS, and releases brakes during trail-braking quickly enough so that ABS does not kick in then either.
- If there is a specific place where ABS engages unusually early, try the threshold braking there and see if it's better.
Some other caveats:
- Stability control sometimes vibrates the brake pedal too, so vibration can be not ABS but stability control. You do not want that type of vibration.
- Long ABS engagement feels like brake fluid overheating - pedal becoming soft and going toward the floor. That's ABS reducing pressure rather than fluid overheating, although it feels very similar. ABS does not put more heat into pads or rotors but can have a similar negative effect on brake feel when overused.
Interesting. That was not my experience. I didn’t take the intro class, but I’ve taken all of the advanced Masters RS and RSR classes (multiple times) and they taught to threshold brake and not stay in ABS. They actually have a specific training exercise to engage ABS but then to immediately modulate out of it.
ABS is where you start, thresh hold braking is where you graduate into - you can not threshold brake if you have no feel for how much deceleration in short time is possible - abs let’s you see what’s possible in a straight line and how hard you can actually go - most novices and intermediates are too
soft and too soon and too long on the brakes - you can not start out with thresh hold braking - people have no idea - and you can live with threshold abs braking for a very long time before you need to transition to more nuanced avoidance of abs but being at or close to the limits of abs - mix in changing conditions and inconsistent hpde environment and most people would do well to hit abs every time - hauling into turn 12 at COTA at 155 mph+ you’re into the brakes for quite a long time…most driver won’t know how to be at threshold for that long and adjust - abs can do a better job
in a cup car at laguna to be cometitive in a series you are adjusting brake bias 3 times a lap add into that threshold braking and not flat spotting the slicks - well abs is just fine honestly it is
Last edited by daveo4porsche; 02-23-2023 at 09:35 PM.
Not to brag but for credibility - I race in a very competitive amateur series and can turn in laps within 0.2s/minute of my pro coach, who is an active pro racer with numerous wins. I review data after practically every day of driving and log everything up to the individual wheel and tire temps and corner heights under load, and generally know what each metric means for car setup or driving technique.
Here is a summary of ABS on track based on everything I've learned so far (applies to the 991 or newer GT3 ABS - older ones were not as good).
1. In a straight line and steady state, ABS will stop the car faster than a human, even at threshold-braking. Getting into ABS during straight-line braking will be the most efficient way to brake. It's easy to prove by data. Even if you can perfectly put the pedal pressure at just before the lockup level (most people can't - they just brake too lightly so ABS does not engage), the problem is that grip changes and the balance of grip between axles changes over time, triggering ABS & EBD. So completely avoiding ABS reaction inevitably means that you are leaving braking force on the table. But there is a catch.
2. Engaging ABS has a cost - brake pads can wear faster or even crumble if worn/overheated due to vibration, and can also leave uneven deposits - many have seen multiple overlapping "stamp imprints" of a brake pad on a rotor - that's typically what a result of ABS action with overheated pad looks like. It may cause vibrations and uneven braking in the future.
3. You do not want to engage ABS during weight transfer. For example, if you slam the brakes so quickly the front wheels start to lock up before the weight transfers to them, ABS will engage prematurely and not allow full brake pressure to build up, which will reduce deceleration and delay the weight transfer, creating a kind of a negative feedback loop.
4. Always make sure you are out of ABS sufficiently before the turn-in point. The problem with ABS is that it prevents knowing exactly how far beyond the threshold you are - you could be pushing the pedal 1% stronger than threshold or 50% - it will feel the same. And when you start turning in and gradually releasing the brake, you need to index the brake release from the threshold. Let's say you know you need to be at 60-70% of the threshold the moment you start turning in. If you are in ABS, you will have no idea whether you need to reduce the pressure by 30% or by 60% because you cannot feel how far past the threshold you are pushing into the ABS zone. So it's important to be out of ABS and feeling the brakes before starting to blend braking and turning, and not get into ABS while turning (that just does not work well, too long to explain why).
5. Some anomalies of track surface can make ABS suboptimal even in the straight line - typically it happens when one wheel gets very unweighted or in the air, so it does not provide braking force, and that creates a force that rotates the car (on one side two wheels brake but on the otherside only one). ABS/EBD will try to compensate for this force to avoid rotation or spin, but that may be counter to the driver's intention. In such cases I would not go into ABS if possible or turn it off. But if that happens, you will know exactly where it happens - it's noticeable.
So, unless there are special circumstances, I would drive an ABS car like this:
- Quick but gradual brake application, making sure ABS does not engage before the weight transfer completes (it is very quick, though in the 992 generation and especially in the RS)
- During straight-line braking, feel free to (gently) dip into ABS for best performance (unless brakes are starting to get greasy due to pads overheating). If anything, it's a good way to understand where the threshold is - otherwise, how will you know? In non-abs cars, racers slightly lock up wheels during warm-up to know, for example. In ABS cars, you dip into ABS.
- Before turn-in point, make sure to release brakes enough to not be activating ABS, and releases brakes during trail-braking quickly enough so that ABS does not kick in then either.
- If there is a specific place where ABS engages unusually early, try the threshold braking there and see if it's better.
Some other caveats:
- Stability control sometimes vibrates the brake pedal too, so vibration can be not ABS but stability control. You do not want that type of vibration.
- Long ABS engagement feels like brake fluid overheating - pedal becoming soft and going toward the floor. That's ABS reducing pressure rather than fluid overheating, although it feels very similar. ABS does not put more heat into pads or rotors but can have a similar negative effect on brake feel when overused.
Thank you, you detailed exactly what I summarized in post #19.
Not to brag but for credibility - I race in a very competitive amateur series and can turn in laps within 0.2s/minute of my pro coach, who is an active pro racer with numerous wins. I review data after practically every day of driving and log everything up to the individual wheel and tire temps and corner heights under load, and generally know what each metric means for car setup or driving technique.
Here is a summary of ABS on track based on everything I've learned so far (applies to the 991 or newer GT3 ABS - older ones were not as good).
1. In a straight line and steady state, ABS will stop the car faster than a human, even at threshold-braking. Getting into ABS during straight-line braking will be the most efficient way to brake. It's easy to prove by data. Even if you can perfectly put the pedal pressure at just before the lockup level (most people can't - they just brake too lightly so ABS does not engage), the problem is that grip changes and the balance of grip between axles changes over time, triggering ABS & EBD. So completely avoiding ABS reaction inevitably means that you are leaving braking force on the table. But there is a catch.
2. Engaging ABS has a cost - brake pads can wear faster or even crumble if worn/overheated due to vibration, and can also leave uneven deposits - many have seen multiple overlapping "stamp imprints" of a brake pad on a rotor - that's typically what a result of ABS action with overheated pad looks like. It may cause vibrations and uneven braking in the future.
3. You do not want to engage ABS during weight transfer. For example, if you slam the brakes so quickly the front wheels start to lock up before the weight transfers to them, ABS will engage prematurely and not allow full brake pressure to build up, which will reduce deceleration and delay the weight transfer, creating a kind of a negative feedback loop.
4. Always make sure you are out of ABS sufficiently before the turn-in point. The problem with ABS is that it prevents knowing exactly how far beyond the threshold you are - you could be pushing the pedal 1% stronger than threshold or 50% - it will feel the same. And when you start turning in and gradually releasing the brake, you need to index the brake release from the threshold. Let's say you know you need to be at 60-70% of the threshold the moment you start turning in. If you are in ABS, you will have no idea whether you need to reduce the pressure by 30% or by 60% because you cannot feel how far past the threshold you are pushing into the ABS zone. So it's important to be out of ABS and feeling the brakes before starting to blend braking and turning, and not get into ABS while turning (that just does not work well, too long to explain why).
5. Some anomalies of track surface can make ABS suboptimal even in the straight line - typically it happens when one wheel gets very unweighted or in the air, so it does not provide braking force, and that creates a force that rotates the car (on one side two wheels brake but on the otherside only one). ABS/EBD will try to compensate for this force to avoid rotation or spin, but that may be counter to the driver's intention. In such cases I would not go into ABS if possible or turn it off. But if that happens, you will know exactly where it happens - it's noticeable.
So, unless there are special circumstances, I would drive an ABS car like this:
- Quick but gradual brake application, making sure ABS does not engage before the weight transfer completes (it is very quick, though in the 992 generation and especially in the RS)
- During straight-line braking, feel free to (gently) dip into ABS for best performance (unless brakes are starting to get greasy due to pads overheating). If anything, it's a good way to understand where the threshold is - otherwise, how will you know? In non-abs cars, racers slightly lock up wheels during warm-up to know, for example. In ABS cars, you dip into ABS.
- Before turn-in point, make sure to release brakes enough to not be activating ABS, and releases brakes during trail-braking quickly enough so that ABS does not kick in then either.
- If there is a specific place where ABS engages unusually early, try the threshold braking there and see if it's better.
Some other caveats:
- Stability control sometimes vibrates the brake pedal too, so vibration can be not ABS but stability control. You do not want that type of vibration.
- Long ABS engagement feels like brake fluid overheating - pedal becoming soft and going toward the floor. That's ABS reducing pressure rather than fluid overheating, although it feels very similar. ABS does not put more heat into pads or rotors but can have a similar negative effect on brake feel when overused.
Agree with all of this, except I'm pretty sure I read in the 991 GT3 owner's manual (I think the track manual) that excessive use of ABS will overheat the brake system. My experience bears this out, because I had soft pedal that didn't go away, even when not braking close to threshold.
Addendum:
Here's what is says in the "911 GT3 Driving on the Race Circuit Manual":
"ABS braking
In addition, repeated braking in the ABS control range results in much higher temperatures in the brake system than controlled braking just before the ABS activation limit."
Agree with all of this, except I'm pretty sure I read in the 991 GT3 owner's manual (I think the track manual) that excessive use of ABS will overheat the brake system. My experience bears this out, because I had soft pedal that didn't go away, even when not braking close to threshold.
Yeah, if it does not recover right away, it's probably overheated. Could be overheating the actual ABS/EBD/ESC pump module? I don't see how the brakes themselves would produce more heat - it's the kinetic energy of the car (speed squared times mass) converting into thermal energy, so the heat produced will be the same with or without ABS. In any case, if something overheats, that's a good reason to do it less
Yeah, if it does not recover right away, it's probably overheated. Could be overheating the actual ABS/EBD/ESC pump module? I don't see how the brakes themselves would produce more heat - it's the kinetic energy of the car (speed squared times mass) converting into thermal energy, so the heat produced will be the same with or without ABS. In any case, if something overheats, that's a good reason to do it less
I think the fluid boiled, since bleed or flush fixed it. Never had the pedal go soft after I trained myself to only minimally use ABS, if at all.
I don't understand why ABS would increase the heat either - I don't even have a hypothesis - but if Porsche says that's what happens, I guess I'll take their word for it.
Bosch’s ABS M5 Kit Porsche Cup manual indicates that passenger car ABS provides braking performance that is less then optimal.
ABS in Motorsport
The ABS function is a compromise between drivability and braking performance. Drivability is the primary focus for passenger based vehicles. The ABS is designed to keep the passenger vehicle maneuverable and stable under any circumstances and under any conceivable driving conditions. In a motorsport context, this compromise shifts towards braking performance, as experienced drivers can still control a slightly unstable vehicle. Together with different tire structures and higher braking potential, a racecar is capable of greatly increased deceleration rates. To consider different chassis tuning and tires, ABS M5 Porsche Cup Kit has eleven control settings plus an OFF-position. With this, the driver can choose the best setting for his vehicle. For calibration drives, the ABS function can be deactivated separately, whereby all ABS sensor signals are transmitted and processed furthermore (OFF-position of the ABS switch).
The EE YouTube video presents a compelling case. However estimates of vehicle velocity, and the tire slip ratio curve need to be determined and there is plenty of slop for less than optimal braking performance based on uncertainties in these parameters. Here is how vehicle velocity is computed as explained by an engineer (control systems engineer, software developer, embedded systems junkie, aspiring mathematician 8y) from Bosch.
Originally Answered: How does the ABS system calculate the vehicle speed?
Note: I previously worked on ESC (electronic stability control) systems at Bosch. The systems I worked on included ABS, TCS, and VDC functions (among others). This answer does not contain any trade secrets, intellectual property of Bosch, or anything like that.
In short, it largely depends on the vehicle configuration. You will typically see vehicle speed being a weighted average of the wheel speeds, with some limits imposed.
Any un-driven wheels will be typically have a larger weight associated with them while the vehicle is not braking. Some vehicles intentionally leave one rear wheel un-braked during ABS events so that the vehicle speed can be more accurately estimated (also for vehicle stability).
Additionally, the ABS system typically has a longitudinal acceleration sensor (Ax - the 'x' direction being forward/backward from the driver's point of view) which is integrated and also plays a role in the estimated vehicle speed. Typically it is a small role, but it does come into the estimation, especially in 4-wheel-drive or all-wheel-drive vehicles.
Nice information above. I personally try to stay out of ABS in my GT3, simply because I don’t want my muscle memory to rely on it when I jump into my 1973 911
Thanks gentlemen for giving such insightful replies to what I had initially thought was a straightforward question. Special thanks to MaxLTV for taking your time to explain the concept in detail. Appreciate it.
I'm fascinated by all the replies on this thread. For reference I'm certain plenty of you are better and faster drivers than I am, but I'm an advanced track driver and been told I'm quick. 100+ track days, although I'm down to 4 a year now. I would say I'm better, relatively speaking, at braking good into, vs accelerating out of, the corner (topic for another time!). I call myself a "threshold braker." Maybe I'm using the term incorrectly but when I say that I mean that I'm braking smooth but late and very hard, right up to where the ABS would kick in. Sometimes it still does, which I take as a teaching moment. From trial and error I've found I'm faster that way vs just using ABS. It also feels better to me (although I agree with the poster who said beginners are better off using abs to start then backing off and learning to dance right up to the edge). Never really thought about all the reasons why faster but many others have hit on some here: car balance, minimizing overheating and brake fade, avoiding "dynamic" friction, etc. BTW when I bed in my track brake pads I use the same braking technique. No ABS.
That said, if you're in an emergency situation where say you have to stop as fast as possible on the freeway to avoid an accident, then yes, smash the pedal all the way down and use the **** out of ABS. none of the benefits of non abs braking exist in that scenario.
The big decider to me for how to do this is when i get in the car with professional or very fast drivers, including at PEC. When they're "going for it" they're not intentionally using ABS.
Quote by GT3Laguna…’ That said, if you're in an emergency situation where say you have to stop as fast as possible on the freeway to avoid an accident, then yes, smash the pedal all the way down and use the **** out of ABS. none of the benefits of non abs braking exist in that scenario.
From my understanding, (and I could be very wrong) ABS braking in an emergency situation, is designed to allow the most inexperienced driver to keep control of the car and brake in the shortest possible time. Key words here are “allow the most inexperienced driver to keep control of the car”. Personally I feel I can stop/slow down a car faster without getting in to the ABS. I don’t like the way the pedal feels, I don’t like the way car feels when ABS is activated.
I copied this link from another thread. Looks like we all have our opinions and that’s “ok’ speaking for myself, I try to learn something new every time I’m on the track and use what works best for me.
02-23-2023, 08:48 PM
