09-04-2018, 10:18 AM | #1 |
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Threshold braking or letting abs do its thing
I shoot for threshold braking, but sometimes I over brake and abs kicks in. I back off to reset then reapply threshold. Another member, pruettfan mentioned at M-school they teach keeping the abs on once it kicks in.
So 2 questions: - once abs kicks in is it really better to leave it on, and why? I can image it might be the safer thing to do, but is it the faster thing to do? - does the M2 abs outperform threshold braking? |
09-04-2018, 12:18 PM | #2 |
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I can't imagine you letting off the brakes to turn off ABS then re-applying pressure to get to threshold will result in shorter braking than just letting ABS run it's coarse.
As for question 2, I would think that any modern car's ABS will outperform threshold braking. I assume that any sort of measured braking test that results in the shortest distance possible is going to have ABS kick in. |
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09-04-2018, 12:26 PM | #3 |
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If you could threshold brake right at the limit of adhesion every corner, every lap, you would be quicker. But, that’s impossible due to constantly changing track and tire conditions, and modern ABS will react quicker than a human to a tire starting to lock up. So, using the ABS when it kicks in is quicker than resetting.
However, slamming the brakes and using the ABS every time will overwork and overheat the calipers and fluid, and you’ll get fade, burnt dust boots, etc, even with track pads and fluid. Since I race older BMWs with not nearly as good ABS as the M2, I try to stick with threshold braking. If ABS kicks in, I go ahead and use it for that braking event, vs resetting, and try to threshold the next time around. So, a hybrid approach. That way, you’re still training your brain and foot to detect threshold, and you’re not overworking the braking system. |
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09-05-2018, 03:04 AM | #4 | |
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I run track pads (Pagid RS29), proper track fluid and live in ABS as I have been taught by the professionals. Comparing the braking data between track pads and OEM shows I spend far less time on the brakes with track pads. The calipers do change color over time because of the heat and yes the rubber boots brake down but neither of those things are a result of ABS braking they are because of the heat generated braking hard ABS or not you will generate tremendous heat with a 3300 plus lb car pushing towards 400 hp. I run 20 min sessions at a very respectable pace with Cup2 tires, the key to not developing fade is all in the prep. ABS systems are widely used in sports car racing because they work, you should use the system that is developed for this purpose. Of course old ABS and traction control systems are totally different animals than these modern systems. |
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09-05-2018, 07:05 AM | #5 |
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I would easily get fade after 15min with track fluid and pads and the OE brakes if I was constantly using the ABS.
Also, Pagids don’t hold up as well under high heat as PFCs, as I’ve destroyed a cpl sets. Last edited by ZM2; 09-05-2018 at 07:11 AM.. |
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09-05-2018, 08:33 PM | #6 |
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I'm pretty new to the track, and threshold braking is certainly more fun to me, regardless of whether ABS is faster and more consistent. Now don't get me wrong, when an F1 team shows up at my HPDE looking to recruit their next 48 year old rookie, I'll totally go ABS. Might even turn my a/c off.
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09-05-2018, 09:46 PM | #7 | |
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09-06-2018, 09:01 AM | #8 | |
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09-07-2018, 01:22 AM | #9 |
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I try to stay out of ABS, I like the feel and control of the car with threshold braking, car feels like an extension of my inputs. A lot of that connection is lost for me when in ABS.
Once in ABS, I consider it a useful tool for the moment, but it usually means I have botched something. This of course is specific to my driving style, others I run with use ABS a lot more than I do, and it works fine for them. However, at the end of the day, although we might run similar lap times, I tend to leave the track day with less abuse to my brakes. I don't fault the ABS directly for this difference, but probably the more aggressive braking style of one who is constantly in ABS. I guess take that for whatever it is worth. Regarding the original question, agreed, generally once you are in ABS you have to follow through. However, there are times when I roll out of ABS and back to threshold, but it has to be the right situation when it is not going to compromise control of the car. Last edited by MINI135i; 09-07-2018 at 01:31 AM.. |
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09-09-2018, 11:31 PM | #10 |
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OP, you asked for my opinion in another thread so here it is
I'm not a huge fan of engaging ABS at track even though it's well proven technology with various benefits. It almost feels like cheating. Once engaged, backing off might not be the best move depending the situation (speed, how smoothly you do it etc). I'm no track pro by any means but I have 15+ track days and I also attended Bondurant Racing School for their 4-day GranPrix Racing class last year for my SCCA license. We were never advised to use ABS. In fact, we had several exercises with different cars to find that brake threshold without engaging the ABS. I believe it wasn't necessarily because threshold braking outweighs ABS. They just prepare you for racing with different cars in different circumstances. For instance, they could have given us auto cars for potentially smoother, faster lap times but we went thru various heel-toe exercises with Viper TAs and tracked 4-speed manual Formula Mazdas (no ABS available). That being said, I might be faster if I take advantage of ABS just like I might be slightly faster with DCT but I prefer threshold braking without engaing ABS (just like 6MT over DCT) simply because I think the former is more challenging hence more rewarding, at least this is how I have been taught/trained |
09-10-2018, 10:32 AM | #11 |
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Thanks all for the replies. I think I’ll keep with my plans to stay out of the abs as much as possible, but let it do its thing if I trip it.
I’m still struggling to understand the physics of how in ideal situations abs can stop you faster, but maybe that’s just it there’s no such thing as ideal on the track as many have mentioned conditions are constantly changing. |
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09-12-2018, 12:22 AM | #12 | |
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Your original question was about if once ABS kicks in if you should release and re-brake I believe. That would increase your braking distance and confuse the ABS system. I drive my track days at about 8/10ths I would say and us Cup 2 tires which offer tremendous grip, combined with dedicated track pads it would take a ton to get to the point where ABS would kick in but it still does occasionally and when it does I allow it to do what it does best. On the regular performance tires of course ABS will kick in far more often at the pace I drive on track. |
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09-14-2018, 01:01 PM | #13 | ||
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So basically what you said in the first paragraph is right - attempt to threshold brake, but err on the side of too much brake. If ABS kicks in, then next time on that corner you can ease off a tiny bit. In my opinion, I wouldn't worry too much about it, the lap time gained in minimal in comparison to mastering other skills (such as trail braking) first. Some discussion about ABS here: https://www.quora.com/In-a-car-equip...eshold-braking |
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09-14-2018, 02:58 PM | #14 | |
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In regards to the guidance from the excellent instructors at M-School's, you have to think about where they are coming from in the bigger picture. M-School is not a racing school or even a track driving school for that matter, it is a performance driving school where the ultimate goal is on-road safety and car control. The school is also teaching to the lowest common denominator and not to the advanced student who is blending braking, turning and actually braking less because they are carrying more entry and corner speed. So long story short the syllabus calls for ABS braking as that is the safe answer, not necessarily the fastest answer. |
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09-16-2018, 07:02 PM | #16 | |
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In general I believe you are correct about the guidance of the instructors but I have to say in the Advanced M School program they are teaching to students with track experience and are teaching to maximize lap time. Most students in my class had 5 years or more of track experience and the school it taught at a very high pace on the Thermal track. Having said that we all know that it is not a racing school nor is it intended to be the end all of coaching and education for a driver looking to improve. As I stated above when I went to dedicated track pads and Cup2 tires I found that ABS pretty rarely kicks in as that combo provides tremendous grip and the amount of time spent on brakes is far less. One final point is most of the Advanced M School is taught on M3/4 with carbon brakes that tolerate heat and brake far more effectively than the brake systems on our M2. They limit the M2 to the autocross and some low speed exercises because of the brakes. Last edited by pruettfan; 09-16-2018 at 07:08 PM.. |
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08-15-2022, 09:38 AM | #17 | |
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08-25-2022, 06:12 PM | #19 | |
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Also no vehicle ABS outperforms threshold braking. Point of ABS is to maintain steerability, not to achieve min stopping distance. Also this is limited by information available to the brake system. You have to know the exact speed of the car to know how much slip the wheels have. If all 4 wheels are sliding, you no longer know exact speed of the car based on wheel speed sensors. To maintain knowledge of exact speed at any given point brakes are released off of 2 wheels, while the other 2 are slipping. This way you can maintain an accurate reference. A fine tuned human can maintain ~4-6% slip by gut feel, preventing the need to release brake pressure during the stop on any of the wheels. That's why well executed threshold braking always beats ABS in stopping distance. It is possible to develop ABS that matches or maybe even beats the driver best effort, but it would require additional high resolution, high frequency speed measurement capability which doesn't depend on the wheel speed sensors. And that gets expensive.
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08-25-2022, 06:17 PM | #20 | ||
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08-26-2022, 05:25 PM | #21 |
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All model years of M2/M2C have a vacuum booster, so you are connected to the pedal. It will vibrate, and you will hear the tires squeal and release when in ABS. The ABS light only goes on when there is a problem with the system.
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08-26-2022, 05:29 PM | #22 | |
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