Braking, Braking...Damned Braking!!
#31
Rennlist Member
Read about black ice mode 997 and 996 cars can get into. Typical scenario for that is stabbing bakes on a bumpy track when front axle is on the way up (underloaded) and rear axle is on full grip. It is very important on those cars toi apply full brake pressure when front axle got preloaded by squeeze, if braking zone itself is bumpy - be careful. In your 944 car it may not be an issue but any 997 car with regular street ABS may lock up you brake pedal. Search 997 gt3 forum about this.
#32
Rennlist Member
Stock ABS versus motorsport ABS is a really apples and oranges. The ability to control unweighted wheel slip in the braking zone is just not possible without an advanced ABS system. You have one pedal to work with while ABS has and effective use of up to 4 zones of application. Stomping on the pedal exceeds the control system limits and often requires more or excessive pedal pulses by the system to compensate for the adverse use of ABS. Learn to use ABS to when you can feel the reaction only in the steering, but not at the pedal itself and you will be really using the ABS properly. Patrick Long even endorses this technique and has offered up a good article on how this is a track advantage. Can you outbreak and ABS system? Stock or a close derivative yes. Bosch motorsport M4 system, I doubt it.
#34
Rennlist Member
I agree 100% with you with the only exception being if your in rain conditions and have a properly programmed ABS system that "sorts" out the chaos. At that point being a bit brave and aggressive on the ABS works, but its risky.
#35
Rennlist Member
IMO, regardless of what kind of car & suspenion we are driving, the key take-away in braking, like all other transitions (longitudinal and lateral) we cause in the car, is to reduce the drama of the weight transfer caused by the transition.If you can pay attention to where the mass of the car is moving in transitions like braking, and work to reduce the drama of the movement, the car will be a better partner for you...
#36
The Penguin King
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IMO, regardless of what kind of car & suspenion we are driving, the key take-away in braking, like all other transitions (longitudinal and lateral) we cause in the car, is to reduce the drama of the weight transfer caused by the transition.If you can pay attention to where the mass of the car is moving in transitions like braking, and work to reduce the drama of the movement, the car will be a better partner for you...
#37
Three Wheelin'
Stock ABS versus motorsport ABS is a really apples and oranges.
The ability to control unweighted wheel slip in the braking zone is just not possible without an advanced ABS system. You have one pedal to work with while ABS has and effective use of up to 4 zones of application.
Patrick Long even endorses this technique and has offered up a good article on how this is a track advantage. Can you outbreak and ABS system? Stock or a close derivative yes. Bosch motorsport M4 system, I doubt it.
IMO, regardless of what kind of car & suspension we are driving, the key take-away in braking, like all other transitions (longitudinal and lateral) we cause in the car, is to reduce the drama of the weight transfer caused by the transition.If you can pay attention to where the mass of the car is moving in transitions like braking, and work to reduce the drama of the movement, the car will be a better partner for you...
Just hoping to add some insight to some of the modern capabilities of the electronics in the vehicles we drive and track. That little black box has a lot of capability but the understanding of its function tends to be way too mysterious.
#38
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I've been through this as well. You start to feel the pedal tickle the bottom of your foot, so you don't add anymore pedal pressure, but if you give it a little bit more you will be able to go a little bit deeper. The real trick to the stock vs. motorsport comparison lies in what has been done to the vehicle. A stock unit is setup for stock tires (or something generally close in performance) and stock brake pads. As soon as you start bolting on sticky tires and super high co pads the driver could be able to beat it because now you're working outside the design envelope for the what the system was tuned for. That is the advantage to the Motorsport unit in that the driver can adjust it for what is on the vehicle. It's similar in concept to an engine controller. Once who start making big changes it's simply beyond the design intent of the initial vehicle, which is why you go out and get it tuned. The motorsport unit acts in a similar fashion.
If I remember right, you do braking systems and ABS for a living, right?
#39
Three Wheelin'
Yep. Braking, traction control, and stability control for GM (formerly Bosch). With the performance models we do a lot of track work to make the car work and work well when owners put it on the race track. When I started I had only driven non ABS/TCS vehicles on the track and have learned a TON about how to drive with the system first hand. Each time I lean on the system it has only made me faster (particularly the ABS). It simply has more finesse and works significantly faster than the driver could hope to match.
#40
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We're going a little off topic, but how does the ABS decide when to start? Is it just looking at a rate of change for the wheel speed or is it also taking into account long. G, yaw, etc?
#41
Three Wheelin'
The most basic explanation is that for a straight line stop the controller looks at two main inputs, percent of tire slip and wheel acceleration. Now for the initial activation the thresholds of these values are a bit higher such that ABS does not activate too early as well as reduce sensitivity to bumps and pot holes. Now, once you start turning the wheel there are adjustments to the entry conditions based on lateral.
#42
Here is a good example of how not to brake. Or how to break (your axle)
http://m.jalopnik.com/5946327/watch-...ium=socialflow
Talk about not managing weight transfer!!!
http://m.jalopnik.com/5946327/watch-...ium=socialflow
Talk about not managing weight transfer!!!
Last edited by Doug007; 09-26-2012 at 11:09 AM.
#43
Rennlist Member
Thread Starter
Just to digress somewhat fellas, the only abs I have in my car is my left/right foot. The OEM brake booster setup has been removed and it’s running a Tilton dual m/c pedal setup. We’ve setup the Motec SLM unit to show increasing lights when approaching lockup via a predetermined rate. This will take a bit of getting used to.
Using Van’s 2nd chart from post # 15 and looking at the Black line in particular, this to me shows essentially very little or no squeeze at all. From what I’m lead to believe this is a desired trace. Yet I can’t reconcile this and squeeze in the same braking moment. Am I just not subtle enough to distinguish that there is a very brief element of squeeze even in a trace like this? I’m aware that there will be a difference from street to race car.
Using Van’s 2nd chart from post # 15 and looking at the Black line in particular, this to me shows essentially very little or no squeeze at all. From what I’m lead to believe this is a desired trace. Yet I can’t reconcile this and squeeze in the same braking moment. Am I just not subtle enough to distinguish that there is a very brief element of squeeze even in a trace like this? I’m aware that there will be a difference from street to race car.
#44
Rennlist Member
Patrick, for your purposes I think you should look at the pressure vs time chart on post #25. The black trace shows an immediate stab from baseline. By contrast the squeeze in the red or blue is not huge, just a little chassis settling in the curve before the line goes ballistic, that little curve is it. Once the chassis is settled you are free to quickly load it. It's very subtile, you're not talking about much pressure in the initial application don't think you can see it in the distance trace. You'll develop better skills without the ABS, fine for threshold braking but too often a crutch...
#45
Rennlist Member
Thread Starter
Thanks JR. I hate to flog a dead horse but this concept has been poking around in my tiny little mind and irking me so much so that threads get created. Especially in the situation of not being able to get out there and practice which gives more time for idle thoughts.