Talk:Anti-lock braking system/Archive 1

Archive 1

Archive 2

why ABC for ABS?

On 13 google hits for "Antilock brake controller". "Antilock brake system" gets 4,930.

Does it work at low speeds?

Hi, I have read the car bibles article on braking, which says:

"The hidden gremlin of ABS - what they don't advertise. If you look at the statistics for crashes, a large percentage of them are "fender benders" - low-speed impacts that only do a little damage and so slow that the vehicle occupants are in no danger. Less than 15mph normally. I'll give you one guess what the typical "minimum activation speed" is for ABS. That's right. Your average ABS system is useless much below 15mph. Seriously. Try it yourself. Find an empty road on a slight downhill grade - even better if its on a dewy morning. Run your ABS-equipped car up to about 15mph and jam on the brakes as hard as you can. The car will skid to a stop and the ABS system will remain totally silent."

http://www.carbibles.com/brake_bible.html

Is this true? If so, should it be included in this article. Thanks!! --Turtle 18:38, 1 June 2006 (UTC)

Yes it is true. ABS is deactivated at low speeds because the SAFETY advantage is minimal, but the difficulty of making it work at low speed is very great. A locked wheel is the best way to stop on many surfaces at low speed.

Greglocock 01:31, 2 June 2006 (UTC)

Effectiveness

I don't think you can make the absolute statement that ABS will NEVER increases braking distances on tarmac, wet or dry. The reason I say this is that with ABS the slip velocity oscillates around the optimum. With conventional brakes a truly skilled or lucky driver could hold the wheel at the optimum slip velocity.

Also, the calibration has to be a compromise between wet and dry road conditions. I don't know how much the optimum slip velocity changes with surface water, but would hazard a very informed guess that the optimum slip velocity for wet tarmac is significantly lower than for dry tarmac.

However if you have data that shows otherwise I'd be happy to agree.

Cheers

Greglocock

Background

Maybe some words on what ABS is supposed to do would be in order. What happens when brakes lock and how does ABS counter this?

Good suggestion. GL

Invention

The Dunlop "Maxaret" system was introduced on the Jensen FF way before this, in the mid-late 1960s. Just because it didn't have the name "ABS" shouldn't mean the article shouldn't talk of it -- this isn't a Bosch ad. I'm going to be researching the facts on earlier ABS systems to get this article a bit more neutral. —Morven 10:31, Jun 12, 2004 (UTC)

Good call, the Bosch Automotive Handbook has an excellent overview of the Lucas system, which I suspect is somewhat based on the Maxaret. greglocock

First edit by John Gwynne

> How much such systems actually reduce braking distances on bitumen is a subject of debate and depends, in any case, on driver skill. A moderately skilled driver capable of cadence braking would get little benefit from an ABS system compared to a novice driver.

However since few drivers have any significant skills, understandably the real world demands that a lowest common denominator approach is taken.

On what do you base this claim? --JonGwynne 23:18, 8 Oct 2004 (UTC)

Well let's see. What percentage of drivers know how to cadence brake? What percentage of those drivers have the presence of mind to use it in an emergency? Is the product of those two percentages likely to be greater than 50%? Common sense and experience tells me that most people lock the front wheels, and leave them locked. GL

>The recommended technique for non-expert drivers, in a typical full-braking emergency, in a straight line on a highway, is to press the brake as firmly as possible and to steer around the obstructions. However, in real-world emergencies of this sort, a novice driver will rarely (if ever) retain the presence of mind to do anything but stomp hard on the brake pedal and steer straight ahead.

But apparently they will be able to cadence brake? Ridiculous

That's not what I said. Try reading it again.--JonGwynne 23:18, 8 Oct 2004 (UTC)

True, in detail.GL

>Some automotive engineers argue that is a better practice to design a car so that it is more difficult to lock up the brakes in the first place. This is done by making the car lightweight and balancing the braking system so that the force applied by the driver during a "panic stop" would be insufficient to lock the wheels.

Cite? This implies designing a system that does not exploit the full braking potential of the tyre.

That's simply not true. In independent testing, non-ABS-equipped TVRs and Nobles significantly outbrake other, ABS-equipped vehicles. e.g. Recent testing by Autocar Magazine: TVR Tuscan S, 100-0 in 4.15 seconds, Noble M12 in 4.11 seconds. Compare to a lighter, ABS-equipped Vauxhall VX-220 that took 4.72 seconds. Slightly heavier BMW Z4 4.39.--JonGwynne 23:18, 8 Oct 2004 (UTC)

So what? If they are not on the verge of locking the wheel then they are not exploiting the full braking potential of the tyre, /for that vehicle/. I'm not saying that is a bad decision (although the same exercise on wet roads might reveal why that is not such a great tactic). GL

Speaking as someone who has made panic-stops in a non-ABS-equipped TVR Tuscan on a wet tarmac, I don't have any problem with the idea of making a light car with big tires that grip well enough to stop hard when the brake pedal gets stomped on. What's your problem with it?--JonGwynne 01:20, 11 Oct 2004 (UTC)

You are arguing from a very specialised point of view. Demonstrably normal drivers have a greater difficulty in stopping a car successfully in wet weather. GL

I make no claims to exceptional driving ability. My panic-stop (though simulated) in the TVR was just that: both feet on the pedals (brake and clutch) as hard as possible and steering wheel dead center. I was deliberately trying to lock the wheels to see how the TVR would handle it. It never, even for a split second, lost control and stopped in a perfectly straight line faster than I ever hope to stop again. If it hadn't been for the seat-belts catching me, I'm quite certain I would have broken ribs on the steering wheel. My point is that ABS isn't the magic-bullet that some people would like car-buyers to think it is. A properly-designed car can stop just fine without it. And, if a small company like TVR with a shoestring development budget can do this, there is absolutely no excuse for a big carmaker not to follow suit.--JonGwynne 22:49, 11 Oct 2004 (UTC)

>In gravel or snow, there is no question that ABS increases braking distances. On these surfaces, the action of the wheels locking causes them to dig into the material and create a buildup of ahead of the locked wheels which helps stop the vehicle more quickly. ABS prevents this from occurring. Some ABS controllers attempt to mitigate this problem by slowing the cycling time, thus letting the wheels repeatedly, briefly, to lock and then unlock again.

Cite? Can you demonstrate that an ABS that has been calibrated for gravel increases braking distances compared with the average driver on gravel?

Increased braking distances for ABS on friable surfaces is well-established, do you dispute this?--JonGwynne 23:18, 8 Oct 2004 (UTC)

No. Reread my comment. GL

So can we at least return this paragraph to the article?--JonGwynne 01:20, 11 Oct 2004 (UTC)

I'd suggest you lose the first sentence, or modify it along the lines of "In gravel or snow, there is no question that ABS increases braking distances over those that a trained driver can achieve."

Why? That isn't the truth. The truth is that while braking on friable surfaces, who is driving is not the point. The car without ABS is going to stop faster because the locked wheels will dig into the surface and built up an increasing mound of material ahead of the car to aid in stopping. ABS prevents this and increases the braking distance. You want to argue about professional drivers vs novices on tarmac, that's one thing - but this is a competely different situation.

>Another effect of ABS on slippery surfaces is that it helps the driver to maintain control of the car under braking rather than going into a skid. With 4-wheel ABS, the driver is able to brake and steer at the same time in order to avoid an obstacle, without having to worry about entering into a skid. The problem is that in certain situations, it is actually better for the car to go into a spin in order to reduce the stopping distance by coverting forward motion into rotating motion.

Cite? breaks laws of physics. Check out conservation of momentum.

Perhaps you can explain what, for example, ice-skaters are doing when they appear to be able to convert their forward motion into rotating motion (and vice versa), seeing as how you're the physics expert. --JonGwynne 23:18, 8 Oct 2004 (UTC)

If you don't understand that then you shouldn't be lecturing other people on brake systems. The reason circuit driving instructors encourage non ABS drivers to spin off when they have lost control has very little to do with stopping distances. GL

I'll take that as a "no" as in "No, you can't explain it and will now drop the subject"--JonGwynne 01:20, 11 Oct 2004 (UTC)

Incorrect and correct respectively. GL

You can't have it both ways. Either explain yourself or drop it.--JonGwynne 22:49, 11 Oct 2004 (UTC)

As a physics student, and one who wants to help out those not so familiar with physics, here is my opinion: If the wheels are turning, the car will follow a certain path, as determined by the direction of the front (sometimes back as well) wheels (see steering). This only requires a certain frictional force to be supplied by the ground. However, if the car skids, then the maximum frictional force will always be applied, which may stop the car faster. (I haven't read the articles I linked to.) Brianjd 11:35, 2004 Dec 23 (UTC

This is just wrong. When objects are sliding, it's called kinetic friction. when there not sliding, it's called static friction. Static friction is always higher. When a tire is turning on the road, it is not sliding or skidding and has the highest friction. Braking forces can be increased until just before the transition between rolling and skidding. I doubt you've ever been in a physics class in your life...this is high school physics.69.122.62.231 17:45, 13 November 2007 (UTC)

Sounds to me like someone is just a little upset that their ABS sacred-cow has been challenged. The fact remains that there are some serious issues with ABS, including the tendency of inexperienced drivers to be lulled into a false sense of security by them which encourages unsafe driving - I've seen this one firsthand. Now, do you want to stifle legitimate criticism of ABS or do you want to work on a version of the article that tells the whole story? --JonGwynne 23:18, 8 Oct 2004 (UTC)

Perhaps I should add, in certain well defined conditions there is no doubt that a skilled driver can outbrake a standard ABS equipped car. I don't know that a skilled driver could outbrake an ABS that has been set up for that particular condition, mind you. For instance in F1 Mclaren (I think) had a car that had different ABS setups for each corner (from memory) which was banned on its second race. However, for the average driver in realistically variable conditions, including poor road surfaces, moisture, variable camber and obstacle avoidance, combined with the average driver's lack of observation and skill, ABS offers him a better chance of survival than standard brakes, in most situations. Whether it also encourages him to drive harder in the first place is an interesting question. GL

I can't speak to any experimental prototypes that McLaren may have been developing, but the fact is that none of their roadcars were equipped with ABS because Gordon Murray felt that the car performed better without ABS. He has repeated stated in various interviews that if he had to design the car over again, he wouldn't have done anything differently. I can only assume that he includes the car's braking systems in this.

And arguing that a professional driver in a non-ABS car may or may not be able to outbrake a novice in an identical car with ABS set up for exactly that condition is a bit of a red-herring. Fact of the matter is that in roadcars, ABS has to be set up in a generic manner to handle a wide variety of conditions which creates a non-optimal setup for most conditions.

As to your final statement about average drivers under variable conditions, ABS offer a "better chance of survival" only in some conditions and not in others. Remember, there are many difference scenarios where locking the wheels to a lesser or greater extent would be beneficial. Another point that this discussion hasn't yet addressed is the contention that the availability of ABS can act to discourange proper development of a car in general and its brakes in particular. Why should a car company spend the development money to keep weight down and to balance braking performance to the car when they can just slap ABS on the car and say "we're done"?

My point is this: even uncontroversial safety-features like seat-belts are not universally effective - there are conditions in which someone in an accident will be killed *because* they were wearing their seat-belts and would have survived if they hadn't been. Airbags are dangerous to children and even smaller adults - particularly in convertibles during rollover accidents. Traction-control and electronic-stability control systems can (like ABS) encourage novice drivers to drive in an unsafe manner because they have too much faith in the ability of these things to compensate for their lack of ability. These are important issues and should be discussed.--JonGwynne 01:20, 11 Oct 2004 (UTC)

I agree, they should be discussed, but those discussions should not be the main part of the Wiki article. As you can see from my "Effectiveness" entry in this Talk, I am not happy with the absolute claim that ABS is always better. When I find some non-proprietary objective data then I will expand the article. GL

Of course they should. Otherwise the article is just an ABS propaganda piece. The well-established shortcomings and failings of ABS must absolutely be part of any discussion on the subject, wouldn't you say? Wouldn't it be a good idea to discuss some of the reasons why world-renowned automotive engineers like Gordon Murray and Peter Wheeler deliberately designed their high-performance cars without ABS specifically because they wanted their cars to have the best braking systems they could and they determined that ABS was an obstacle to this goal?--JonGwynne 22:50, 11 Oct 2004 (UTC)

Compromise edit by Jon Gwynne (14 Oct)

Yes, that is better. You do understand that it is not the weight, per se, of the vehicle that reduces the need for ABS in dry conditions? The reason you can get very good braking performance with big tyres on light cars with low CGs is that there is less weight transfer, and the tyres are operating more nearly in their linear range.

I trust you agree that the weight is the most significant factor involved (though obviously not the only one) in determining the speed with which a car can brake itself to a stop on any surface, with or without ABS. Lower weight means less inertia to overcome. All other things being equal or even equivalent, the lighter car will ALWAYS brake faster.--JonGwynne 18:03, 17 Oct 2004 (UTC)

Sort of. If a car were slightly heavier but fitted with much stickier tyres than a lighter one then the heavier car would win. Leaving the tyre out of the equation is to miss most of the point.Greglocock 06:17, 19 Oct 2004 (UTC)

As I said before, I'll rewrite this when I find some published data on the direct effect of ABS on stopping distances, but I'm losing hope. A direct comparison of the same car with ABS switched on and off is not good enough, since the 'off' case won't have been set up correctly.Greglocock 09:45, 17 Oct 2004 (UTC)

Not sure what you mean about the "set up" here. I remember an article in one of the car magazines a while back that compared the braking performance of a car with switchable ABS. If memory serves, it was a Mercedes. So, in many ways probably not an ideal candidate for this test since the brakes were probably pretty easy to lock up - especially in the wet. Maybe that's what you mean by "set up". --JonGwynne 18:03, 17 Oct 2004 (UTC)

Traditional brake systems have brake proportioning valves, and use different calliper geometries (etc) front and rear, so as to give a reasonable brake balance. ABS cars do not need to do this, they can compensate for significant differences in brake performance wheel to wheel, or axle to axle, by altering the line pressure. Therefore an ABS equipped car with the ABS switched off may not have good brake balance (if it was designed to be switched off then this is, admittedly, unlikely). The Merc test would be a good one, can you find it again? Greglocock 06:17, 19 Oct 2004 (UTC)

But I trust you would agree that it would be better for a car (with or without ABS) to have the brakes set up to provide maximum stopping ability without locking the wheels, right? I trust you would also agree that installing ABS on a car allows the designer (if they choose) to not spend any effort setting the brakes up for maximum stopping abillity because the ABS will prevent any of the wheels from locking up. In other words, you seem to be saying that ABS is a band-aid fix for sloppy engineering. Is that right? Incidentally, I agree with that statement.--JonGwynne 17:56, 21 Oct 2004 (UTC)

Meanwhile here's a couple of references

http://www-nrd.nhtsa.dot.gov/vrtc/ca/capubs/sae1999-01-1286.pdf

Thanks for the link. Unfortunately, they don't make clear the methodology of the studies they cite. I did some digging on the Kahane study and it turns out that it was a simple survey of data from FARS (Fatal Accident Reporting System). There doesn't seem to be any investigation of why (or even *if*) ABS was the determining factor in the reduction of accidents. But, even granting his assumption that ABS was the sole cause for the reduction in accidents, even Kahane admits, when referring to the NHTSA's own tests, "Stopping distances decreased substantially with four-wheel ABS on wet surfaces, but decreased only slightly on dry pavement and increased considerably on gravel"--JonGwynne 17:56, 21 Oct 2004 (UTC)

http://www.ibmwr.org/prodreview/abstests.html

You did know that this was for motorcycles only which, because of their weight and wheel-configuration, have more of an issue with wheel-lock under braking.

Which demonstrate pretty conclusive evidence that ABS is beneficial in the wet, at least.Greglocock 06:33, 19 Oct 2004 (UTC)

I'm not sure I'd agree that is was conclusive, but I would say that it is very suggestive. The problem is that the other aspects of cars have also been improved since ABS was introduced in road cars. Brakes, tires (compound and tread-design), suspension, chassis-balance, etc. have *all* improved dramatically in that same period. To give sole or even primary credit to ABS for the overall improvement in performance is to make an unwarranted (though obviously appealing) assumption.--JonGwynne 17:56, 21 Oct 2004 (UTC)

ABS and NON ABS

ABS only stops a person from locking up the brakes which in turn would make the car stop quicker then if the person had locked up the brakes. A car with bigger disk pads and disks all round could stop faster then a car with ABS on a car with smaller disk pads and disks. But only if the brakes on the first car without ABS was not locked up. Skidding or sliding makes you lose control of the car and will take longer to stop. Also the road conditions and tread type on the wheel will be a great factor in the stopping distance. Richard Mendoza

The article contradicts this - under some conditions, locked wheels build up material in front of them, stopping the car faster. Brianjd 11:48, 2004 Dec 23 (UTC)

The common average driver

This discussion is all very interesting, and quite possibly more informative than the article itself. :) But I'm curious how often the average driver encounters a "friable" surface. I've only encountered gravel in parking lots and back country roads, not exactly places where I usually need to worry about high-speed skids. And the snow-covered roads here in northern Ohio are always packed down solid due to the amount of traffic, and I don't see how a locked wheel is going to dig into the snow in any capacity. Am I missing something obvious here? (And as far as spinning reducing momentum, even if that's true, how often does one have room to spin around uncontrolably on a highway or city street?)

Further, being someone who admittedly knows zilch about cars and only a scant bit of what I learned in high school physics, this article leaves me with the impression that antilock brakes aren't worth it and are ineffective on snowy and icy roads. "The primary benefit of ABS on such surfaces is to increase the ability of the driver to maintain control of the car rather than go into a skid—though loss of control remains more likely on soft surfaces like gravel or slippery surfaces like snow or ice." If this is truly the case, then every manufacturer of antilock brakes should be sued for false advertising, because as far as I'm told, the main purpose of antilock brakes is to prevent skids on snow and ice. So what, are we only supposed to use ABS on wet roads? Or is that one a lie too? I'm not trying to be snarky here, I really would like to know -- I'll be purchasing a new car this year, and had previously thought ABS would be a no-brainer for Ohio winters, but now I'm not so sure. Leaving out ABS would mean saving a few thousand dollars because I could get a lower edition of the model I want.

If you're buying a new car in the US, I doubt that ABS is going to be offered as an option (i.e. something you can safe money by leaving off). Also, even for someone like me who is highly critical of ABS, I am the first to admit that on certain types of cars, it is good to have. In fact, if we really want to get into hair-splitting here, my beef isn't with ABS per se, but with the tendency of car designers to use ABS as a substitute for better car design. Ideally, cars would be lighter and would, therefore, stop more quickly and safely with or without ABS. Without ABS, car companies would have considerable incentive to make cars lighter and more responsive. But with ABS, they simply don't have to. It is cheaper and easier to slap ABS on the car than it is to cut 1,000 lbs from the curb weight. If you're buying a car with Ohio winters in mind, I would recommend looking hard at Saturn. Their use of plastics for body panels has a double benefit - corrosion resistance and cheap/easy replacement in the event of a fender-bender. --JonGwynne 05:50, 21 Jun 2005 (UTC)

Interesting. I can't speak for all car manufacturers obviously, but the car I'm particularly interested in is the Honda Civic, because of its excellent safety ratings and good gas mileage (for an automatic... actually the difference between the manual's and automatic's gas mileage isn't that much). In the case of the Civic, ABS is only offered in the EX trim level, which is $3650 more than the Value Package, but since the EX also throws in other features I can't say for certain exactly how much ABS is adding to the cost. In reality I would probably be going for at least the LX though, so the difference is really only $1900 for me, which is still a nice chunk of change. I have a few friends who bought Saturns in the past few years and they seem to be pleased with them as well. --Birdhombre 12:22, 21 Jun 2005 (UTC)

Also, what our Aussie friend says below about taking driving lessons is an EXCELLENT idea for someone who is going to be driving in tricky winter conditions. There is absolutely no substitute for experience. If I were a passenger in a car, I'd trade all the electronic gizmos in the universe for a driver with a clear head and experience in keeping/regaining control of a car on a slippery road. So, especially if you have a family, ask the dealer if they have a winter-driving class they can sell you as part of the price of the car. You want to get out in a controlled situation where you can practice what to do if the car gets frisky on you. --JonGwynne 05:58, 21 Jun 2005 (UTC)

One last thing, then I'll shut up. Every person I've talked to about antilock brakes (also all non-experts) gives the explanation that, "it's better to tap the brakes repeatedly when you skid on snow and ice, but the ABS computer can do it a lot faster than your foot can, so it's more effective." Is that an oversimplification, or just incorrect? The article doesn't seem to explain it this way, as far as I can tell. But if this is the popular conception among the public, perhaps this notion should be debunked in the article. --Birdhombre 18:36, 15 Jun 2005 (UTC)

That's a simple explanation but not terribly inaccurate. Think of it this way: If you want to stop as quickly as possible, what's the ideal way to do it? Answer: To press down on the brake pedals just hard enough so that the tires don't break traction and start to slide rather than turning. Right? On a dry, grippy surface, this usually isn't a problem. But when things get slippery... that isn't as easy to do because it would require the ability to predict the future (i.e. "If I press harder on the pedal, will the tires lock?"). So, in the real world, there are two options. One is for the driver to manually "pump the brakes" (i.e. press the pedal repeatedly as quickly as possible) - sometimes called "cadence braking". This allows the brakes to work a portion of the time by releasing and then reapplying them repeatedly. The other option is to let an ABS computer do this for you automatically. The computer has a sensor on each wheel and when you put on the brakes it makes sure the wheels keep turning. If one of them stops turning, it assumes that the wheels has locked and releases the brakes for that wheel. Then when the wheel starts turning again, it reapplies the brakes... it then repeats this process potentially hundreds of times every second and, depending on the car, possibly does it independently for each wheel. So, not only is ABS faster than your feet and brain could be, it would also require you to have four feet and four brake pedals in order to try to match it.

The heavier a car is and the more power-assist there is in the brake system, the more benefit the driver will get from ABS. The reasons for this should seem obvious - heavier cars have more mass to stop and are more likely to skid in the first place. Also, heavy vehicles are more likely to have higher-powered hydraulic brake systems which make it more difficult to get the kind of fine control needed for effective cadence-braking. --JonGwynne 05:50, 21 Jun 2005 (UTC)