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Old 6th February 2010, 23:57   #31
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My throw at this is that these systems work by sensing the relative speed between the brake pads and the wheels. If it tends to zero, the pads are released, probably for a short period of time, and then pumped again, till the steady state value of zero relative speed is reached.

As for the arguments related to whether a driver can beat the ABS system, he might be able to, but in a pressure situation when you're travelling at a few hundreds of kilometers/hour, you would be concentrating on the road more than on when to release your foot from the brake pedal, so a driver with an ABS system will win practically, though it's the other way around in theory.

My personal opinion.
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Old 7th February 2010, 02:17   #32
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The ABS system as such, originated in aircraft where the primary concern was to reduce landing distances without having a tyre burst. The kind of ABS systems being talked about here are the so called 1st gen systems which wait for a lock up and then re-distribute brake force. In aircrafts, more advances have been made and the latest systems have a electronic comparator circuit that calculates the ideal wheelspin for a desired ammount of braking and thereafter compares the actual wheelspin with this particular value and thereafter modulates the braking force to achieve this desired wheelspin. Thus in these systems, the wheels never lock. So, even theoretically, these systems will be better than a driver who is capable of threshold braking.
Any gen on such systems being used in road vehicles?
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Old 7th February 2010, 06:30   #33
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[quote=neel385;1720078]The ABS system as such, originated in aircraft where the primary concern was to reduce landing distances without having a tyre burst. quote]

There is a detailed description of various ABS system in the thread "Strange ABS behaviour in Fiat Punto " dated 10th-Jan-2010. If any one is interested to go through.
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Old 7th February 2010, 08:35   #34
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Thanks for the answers, tintin82. Looks like I need to do a detailed checking. Will post my findings.
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Old 7th February 2010, 18:51   #35
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Quote:
Originally Posted by ravikn View Post
Great Thread Mclaren,

I do have one question, I have experienced ABS being effective while breaking on the dry and smooth highways at high speed. However, in city driving conditions, I have encountered couple of times where I have literally stood on the breaks to stop the car and was afraid that my car would hit the vehicle in front ( speed may be in 45-60 kmph).

Any ideas on this. My car is a palio 1.6 GTX SP
At the speeds you've mentioned and in normal city roads, there is very little chance that the ABS would've activated. If you felt this on a road which had a lot of gravel, sand or numerous irregularities there is a chance that ABS would have been engaged. And typically when the ABS is engaged, you'd hear a faint hammering sound like jg..jg..jg..jg..jg when the ABS pump kicks in.

I had a FIAT before and will say that their brakes are not as spot on as Jap/Korean cars.
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Old 7th February 2010, 22:06   #36
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Quote:
Originally Posted by neel385 View Post
The ABS system as such, originated in aircraft where the primary concern was to reduce landing distances without having a tyre burst. The kind of ABS systems being talked about here are the so called 1st gen systems which wait for a lock up and then re-distribute brake force. In aircrafts, more advances have been made and the latest systems have a electronic comparator circuit that calculates the ideal wheelspin for a desired ammount of braking and thereafter compares the actual wheelspin with this particular value and thereafter modulates the braking force to achieve this desired wheelspin. Thus in these systems, the wheels never lock. So, even theoretically, these systems will be better than a driver who is capable of threshold braking.
Any gen on such systems being used in road vehicles?
Neel, this is great stuff! I'm going to read up on this and if you have any good articles already, do link them here. I'm not sure if all of it will be applicable to cars but some of it might.
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Old 7th February 2010, 22:57   #37
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Quote:
Originally Posted by McLaren Rulez View Post
Neel, this is great stuff! I'm going to read up on this and if you have any good articles already, do link them here. I'm not sure if all of it will be applicable to cars but some of it might.
Hey McLaren..the stuff I was talking about is the stuff I actually use and so no real links to give you. If you want more detailed info on how the stuff works, do let me know.

[quote=sudharma;1720116]
Quote:
Originally Posted by neel385 View Post
The ABS system as such, originated in aircraft where the primary concern was to reduce landing distances without having a tyre burst. quote]

There is a detailed description of various ABS system in the thread "Strange ABS behaviour in Fiat Punto " dated 10th-Jan-2010. If any one is interested to go through.
Hey Sudharma..went through the thread...didn't find anything about different generation of ABS systems, just advancements made to 1st Gen ABS systems (when compared to aircrafts)

Last edited by Dippy : 10th February 2010 at 17:30. Reason: Back to back posts. Please use the edit function if posting within 20 minutes of your earlier post.
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Old 8th February 2010, 14:48   #38
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Mclaren rulez quoted some statistics which were from the study he gave a link to. Only that he quotes incidents where ABS increased the danger. Here are others from the same study:
Quote:
Involvements in multivehicle crashes on wet roads were significantly reduced in the cars equipped with ABS: fatal crashes were reduced by 24 percent, and nonfatal crashes by 14 percent. Fatal collisions with pedestrian and bicyclists were down a significant 27 percent with ABS. However, these reductions were offset by a statistically significant increase in the frequency of single vehicle, run-off-road crashes (rollovers or impacts with fixed objects), as compared to cars without ABS. Fatal run-off-road crashes were up by 28 percent, and nonfatal crashes by 19 percent. It is unknown to what extent this increase is a consequence of ABS, or is due to other causes. In particular, it is unknown to what extent, if any, the increase is due to incorrect responses by drivers to their ABS systems, and, if so, whether the effect is likely to persist in the future.
The aggravation cases due to ABS are of situations where significant steer input is made i.e. rollovers/side-impacts/run-off-road etc. This does not make the ABS inferior to non-ABS cars.
There's more data I have found regarding this and would post it. As to OP's questions, can the ABS be beaten manually by the driver? No. The ABS typically works in 20 pulses/sec and that too with precise measurements of slip and impending lock.
More on ABS later. Very nice thread.

This thread is named indicative of information on how the ABS works but the discussion is more on whether ABS can be beaten. To know whether one can manually perform better, we first need to know how it works. As someone said, ABS was invented for aircraft. To know more about how ABS came about, read this:

Anti-lock braking system - Wikipedia, the free encyclopedia

There's another more recent study on the effectiveness of ABS in motorvehicles, here:

http://www.monash.edu.au/muarc/repor...ectiveness.pdf

Here is an excellent article on braking and its types:

footer

It does mention that threshold braking will stop you earlier. Remember that this would only be good for a straight line dead stop. But in a panic situation, will you be able to do that? And given the varying condition of road and your own speed, how safely can you use threshold braking in an actual situation? IMO, not at all. More importantly, with threshold braking, the smallest requirement of steer input may need you to leave the brakes and upset your balance on re-application and the wheels may lock whereas with ABS, steer control is available with you throughout.
Another thing to keep in mind is the initial speed of commencement of braking. At lower speeds (upto around 60 kmph), the distance to stop is the shortest with the wheels locked as against ABS. But this would work only on dry, hard roads and with slightest smoothness (such as on a wet road) reducing friction would have your car skid (under aqua/hydroplaning). As the speed of initial brake application increases, effectiveness of ABS also increases.

Someone mentioned threshold braking by F1 drivers. Sure, they do it and they do it on well known, well laid tracks on vehicles optimised for such performances in situations which are already under control. In aircraft too, you have gauges showing you how much brake pressure in PSI or kg/sq cm you are applying. These things are neither available in road cars nor relevant in an emergency stop situation.

Last edited by Dippy : 10th February 2010 at 17:31. Reason: Back to back posts. Please use the edit function if posting within 20 minutes of your earlier post.
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Old 8th February 2010, 15:26   #39
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@tintin82

Thanks a lot for the response. Is there anything that I should do in order to get better breaking at lower speeds in my palio.
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Old 8th February 2010, 16:09   #40
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Quote:
Originally Posted by tintin82 View Post
This can be due to a lot of reasons. The ABS unit will not kick in until it senses a wheel lock. So if you feel your vehicle drags left even under moderate braking, there might be other reasons at work. Check your brakes to see if the the left rear wheel is too tight.
One quick question though: So in the above case, shouldnít ABS be activated because one wheel was locked up? I donít see this happening, irrespective of the wheel dragging for a 1-2 feet distance at times.
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Old 8th February 2010, 19:07   #41
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The graph Rehan had put up earlier portrays the primitive ABS system response. A modern system vs a human response (the best one at that) might look like this:
Name:  braking.jpg
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Considering that the driver manages to get the orange line close to the blue dashed ideal line in normal conditions, how would it work under panic situations especially when the slip conditions may vary like this [FONT=Arial,Helvetica](In the graph- (a) dry asphalt; (b) wet asphalt; (c) gravel; and (d) packed snow):
Name:  friction coeff vs slip graph.gif
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The car may just go spinning if the slip suddenly develops or if the surface is wet. With ABS, the tires are being braked with slip continuously calculated. Check the extreme video here. This link also gives how to go about threshold and regressive braking (on race tracks):

Threshold braking - Trackpedia

Last edited by Delta Wing : 8th February 2010 at 19:11.
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Old 8th February 2010, 23:03   #42
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Quote:
Originally Posted by ravikn View Post
@tintin82
Thanks a lot for the response. Is there anything that I should do in order to get better breaking at lower speeds in my palio.
You've to be the judge of whether your car had distinctively poor brakes or it's just the Palio effect. Try driving another well maintained Palio to check whether the problem is just in your car alone.

For situations that are not sudden, like for instance slowing down in a signal or junction, make use of engine braking more and use the brakes only to bring the car to a final halt.

Quote:
Originally Posted by CasperRider View Post
One quick question though: So in the above case, shouldnít ABS be activated because one wheel was locked up? I donít see this happening, irrespective of the wheel dragging for a 1-2 feet distance at times.
Unfortunately, I don't think the Scorpio comes with rear ABS sensors. It's front only.
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Old 9th February 2010, 00:02   #43
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From my personal experiences.
ABS increases stopping distances on normal dry tarmac.
ABS increases stopping distances dramatically off tarmac.

ABS helps you to steer while braking, but whats the use when you have no traction on wet or slippery surfaces/ gravel.
Since the ABS tech used by auto companies is such a guarded secret, its hard to know if the ABS tech being provided by one manufacturer is better than the other. A customer will put his money on "ABS" without knowing if hes being shortchanged on the tech front.

Under a panic situation(to prevent an accident) a driver will usually stand on the brakes as hard as possible. With ABS depending on the surface, condition of brakes and tires the braking response will vary... mostly on a rough surface the stopping distance will certainly increase(my experience).
In a non ABS vehicle, the wheels will definitely lock. which wheel/s locks depends on the same factors as the ABS vehicle. You may not be able to steer out of the situation but the stopping distance is lesser in comparison. Quickly Pulsing the brake pedal once on a non ABS vehicle does ensure better braking. Does make me sound old school, but it does work. Achieving braking threshold on a non ABS vehicle is very tricky and includes a lot of human factors apart from mechanical factors. It also requires lot of awareness of ones vehicle and braking characteristics and experience. Chances of such an achievement in a panic situation are mostly very very less.

All the videos and tests done are done on vehicles that have equally worn tires and brakes in good condition and do not replicate various hypothetical scenarios such as poor brakes, unevenly worn tires, poor driver responses, etc.

I will not debate if humans can beat a computer or not, but one things for sure. Having driven both ABS and non ABS vehicles I feel the current lot of ABS tech sold on vehicles isnt really that smart. They need to develop SMARTER ABS systems where the ABS can switch on and off or modify and modulate its actions after sensing all the other factors like poor tires, poor road, poor brakes, poor drivers, etc. Maybe such systems are in existence and are available on super high end vehicles, but unless the other cheaper vehicles have equally smart technology, you may drive a super smart car but some 'not so smart' car will crash into you.

No intention to distract the nature of the discussion here, but just my 2 practical driver cents.

Last edited by jaysmokesleaves : 9th February 2010 at 00:05.
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Old 9th February 2010, 10:37   #44
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Quote:
Originally Posted by tintin82 View Post
Unfortunately, I don't think the Scorpio comes with rear ABS sensors. It's front only.
. Will investigate that too. What the A.S.S told me was that it does have ABS for all wheels. I understand that it does not have EBD, so you might be correct. Thanks again, dude.
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Old 9th February 2010, 12:26   #45
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Quote:
Originally Posted by jaysmokesleaves View Post
I will not debate if humans can beat a computer or not, but one things for sure. Having driven both ABS and non ABS vehicles I feel the current lot of ABS tech sold on vehicles isnt really that smart. They need to develop SMARTER ABS systems where the ABS can switch on and off or modify and modulate its actions after sensing all the other factors...
What we need to understand is that, contrary to popular belief, ABS does not help to stop faster. Period. ABS stands for Anti lock Braking System. It prevents wheel lock and that's it. In panic situation, the driver normally stomps the brake pedal with full force. Thus the tendency for the wheels to lock and induce a spin and thereby loss of directional control is high. ABS helps to prevent wheel lock. That's the end of the story. Its upto the driver to control the vehicle and bring it to a stop.
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