Effect of ABS on Dry Pavement Stopping Distance

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on my dodge dakota I only felt the ABS kick in one time when a truck stopped infront of me. it was scary feeling the peddle pulsating and thought I would never come to a stop. but without ABS I am quite sure I would of slid right in to the back of the truck. so a ABS system can be a blessing and a curse. guess its one of them nessicary evils we have to live with. while working on the B-52 Bombers got to see how a basic ABS system accually worked. its quite simple but I guess its more complicated on todays vehicles. after all those bombers was made in 1960
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but in the ice and snow wouldnt you travel further with no abs compared to abs? your tires would turn into skis when they stop rotating?
 
"but in the ice and snow wouldnt you travel further with no abs compared to abs? your tires would turn into skis when they stop rotating? "

On packed snow and especially on ice I try to avoid 'heavy' downshifts, but in deeper snow the downshifting should help provided it's at a lower speed.
 
quote:

Originally posted by moribundman:
The ABS system will pulsate around that point. A experienced driver can "find" the close to skidding point and do a better job than the ABS system.

I am going to have to disagree here. There are ABS systems that can simply stop the car faster than even the most experienced driver can (by modulating the brakes). And, then again, there are cars with ABS systems where this is not true.

ABS systems that cycle by decreasing brake pressure slowly until traction is found and then increasing pressure slowly until traction is lost, can operate the tire much closer to the edge of traction than any driver can reaslistically hope to achieve, even under ideal circumstances. There may be 25 drivers in the whole world that can achieve better stopping distances than these systems in ideal test setups. Throw in debris on the road, water, leaves, children in the back seet and there is no hope for a driver to achieve as good a stopping distance as these cars. Ferraris, Porsches, some Mercedes, and some BMWs get these systems. Other higher end cars may also get these systems.

Unfortuantely most ABS systems decrease the braking pressure too fast and then increase the braking pressure too fast. Operating like dozens of tiny skids per second rather than cycling around the point of best traction. Even here, though, ABS will beat 95% of all drivers 95% of the time. Many suspensions are not sufficiently stiff (and damped) to enable ABS systems to find the point of best traction.

And then there is the problem of upgrades to the suspension, brakes, tires and wheels. An ABS system has its time constants and valving sized for the tractio of the default tire combination and the rotational inertia of the original tire/wheel/brake rotor combinationi. Changing any of these variables can move the ABS system far away from its optimal performance. No manufacture, that I know of, will give the average back yard mechanic the information required to move the ABS system back towards optimal. (Think Lawyers)

Finally, as tires age they loose traction. You may feel that getting 80,000 miles from a set of tires is saving you money. You might be surprised to find that best case braking performance at 79,000 miles is 30 or more feet longer than identical tires when new.
 
quote:

Originally posted by 1sttruck:
I had forgotten that potentially a big difference on ABS stopping distance is whether one has a stick or auto tranny. Our cars have autos, ABS, front disc and drum rear, and they accelerate going downhill which requires lots of braking, so there is no engine braking, in fact it's anti-engine braking. The truck has a stick, and being a 5.9 liter diesel it has very good engine brtaking, especially with 4wd engaged. I noticed today that when braking to stop while downshfting in the rain while turning that I could chirp the tires, so as expected ABS can't compensate for engine braking with a stick..

ABS still helps, even though it doesn't control engine braking. It will let you use a lot of braking while geared down because you can mash down on the brakes to get full front wheel braking while not locking the rears up any more than the engine braking alone is doing.
 
I had forgotten that potentially a big difference on ABS stopping distance is whether one has a stick or auto tranny. Our cars have autos, ABS, front disc and drum rear, and they accelerate going downhill which requires lots of braking, so there is no engine braking, in fact it's anti-engine braking. The truck has a stick, and being a 5.9 liter diesel it has very good engine brtaking, especially with 4wd engaged. I noticed today that when braking to stop while downshfting in the rain while turning that I could chirp the tires, so as expected ABS can't compensate for engine braking with a stick..
 
My BMW motorcycle has anti-lock,intergrated brakes and I just recently received a warning from BMW Motorad about the ABS system. According to BMW, the anti-lock system on the bikes have a real problem when the road is dry and bumpy. As the wheels oscilate over the bumps, the brake system oscilates the brake pressure, which in turn makes the stopping length more. I, personally have not encountered this, but I could see how this could happen on a washboard type surface. I know this is about auto and light truck ABS systems, but I think the principle is the same.
 
quote:

Originally posted by moribundman:
The ABS system will pulsate around that point. A experienced driver can "find" the close to skidding point and do a better job than the ABS system.
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I am going to have to disagree here. There are ABS systems that can simply stop the car faster than even the most experienced driver can (by modulating the brakes). And, then again, there are cars with ABS systems where this is not true.

So you disagree while agreeing?
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My point was that there are ABS systems that no driver can outbrake.

While your point was that some drivers can.

I disagree that some drivers can the best ABS systems*.

[*]Excluding the 25 drivers in the whold who have the tallent, reflexes, attention, and car in perfect operating order. And, no, none of the magazine drivers qualify in this top 25, and less than 1/2 of the active F1 drivers even qualify!
 
Dark Jedi,

White 03 has it correct.

Snow and gravel will build a wedge in front of the locked tires (think of a doorstop). This will slow a car faster than relying on ABS.

Audi's used to have an ABS off switch for such occasions (maybe still do?)

cheers.gif
 
Anyone that has trained himself well can use thresh-hold breaking and out break ABS especialy on dry pavement. I used to bet people money on this very topic and won the bet everytime!!! Few people though keep themselfs in a well trained state. I used to practice various emergency,offensive,deffensive driveing tech. weekly for a long time.


I am out of practice now but am sure I could still do it.
 
quote:

I disagree that some drivers can the best ABS systems*.

Which are the best, and how is it relevant? Relevant is what's built into current average cars. Those ABS systems can be matched or trumped by a skilled driver on dry pavement.

PS: I am dying to know from where exactly you pulled that number of 25 drivers who can beat the best ABS system. It appears to be an arbitrary random number, but what do I know?
wink.gif
 
quote:

Originally posted by moribundman:
[QUOTEThose ABS systems can be matched or trumped by a skilled driver on dry pavement.

The average driver listening to music or being distraced by kids, etc in the car will benefit bigtime having ABS.
Of course if you take your car to the track and race it regularly, you would in the end beat the ABS system..
 
quote:

The average driver listening to music or being distraced by kids, etc in the car will benefit bigtime having ABS.

You may want to go back and READ what I wrote previously in this thread. I AM an advocate for ABS.
 
quote:

Originally posted by moribundman:
You may want to go back and READ what I wrote previously in this thread. I AM an advocate for ABS.

Sorry I quoted the wrong message..Too much beer drinking this saturday night.. Happy to have you on the ABS "team".
 
quote:

Originally posted by moribundman:

PS: I am dying to know from where exactly you pulled that number of 25 drivers who can beat the best ABS system.


I don't think you really want to know do you?
grin.gif


67.3% of statistics are made up.
 
quote:

Originally posted by rpn453:
... isn't ABS supposed to reduce stopping distance on dry pavement?

no. and this is the flaw in this discussion. abs is intended to help the driver maintain control of the vehicle.
 
I think it IS designed to reduce stopping distance on dry pavement (as well as allow you to maintain control and steer)), because if you lock up the brakes and skid the coefficient of friction will be less than unlocked wheels, at least that is what I remember from my Statics and Dynamics class.... those many many years ago.
 
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