utkinpol

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.

bobt993

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.

J richard

Bob, agreed. The point I was making is slamming on the binders and letting ABS sort it is not a good or effective practice...

bobt993

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.

Veloce Raptor

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...

mglobe

Nailed it.

2BWise

For short braking zones or places where the driver is using the brakes to set the nose or settle the platform no, but for going deepest in the big braking zones..Yes. Mid Oh; Keyhole and Turn 7; VIR; Turn 1, Oak Tree, and the Roller Coaster ABS is going to beat the driver threshold braking. Its simply easier to drive. Find your marker, stomp the pedal, and let the computer sort it out. In these cases you're looking for ultimate braking distances and therefore it is faster.

Not quite as much of you think. The motorsport unit is generally just a paired down version of the stock systems. Such as with Porsche the Bosch unit in the stock vehicles are very close to the motorsport unit they offer.

Bingo! This is one of the biggest advantages to the system. In any braking zone that is not perfectly straight the controller can modulate each individual wheel to its individual threshold based on the normal force that is available to it. It will help trail brake the car in this case as well. As you turn in and unweight the inside wheels there limit reduces and therefore you have to reduce your brake pressure to keep it from locking. With ABS you can simply keep your foot in it.

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.

Sounding like Sir Jackie.

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.

Matt Romanowski

I think this is the key as to why people think that ABS systems are not as good as they really are. The system was programmed with a set of asumptions (tires, pads, max G loads, etc) and when you start going outside those assumptions, the system doesn't work. I was in a new GT3 4.0 for a couple of days at Lime Rock - the ABS in that car is AMAZING!!!

If I remember right, you do braking systems and ABS for a living, right?

2BWise

It is. Bosch system as well. I never drove that vehicle, but I was in contact with the guys that were tuning it and saw a lot of the data. Porsche's tuning philosophy is a bit different than what was done on the Corvette (the program I was working at the time) but it is very effective. That's a perfect example of what can be done with a stock vehicle when the ultimate goal is performance. The other upside is that anything below a true racing slick with play nicely with the ABS system in that car since the factory tires are very close in performance to a lot of the R compounds on the market.

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.

Matt Romanowski

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?

2BWise

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.

Doug007

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!!!

333pg333

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.

J richard

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...

333pg333

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.