Anti-Locking Brake Systems - bad, bad, (generally) bad.

by Mark Zaugg 14. November 2006 01:00

ABS is one of my favourite rants ever.  I'm not a fan.  I don't believe they alone make a car one bit safer than a car not equipped with them.  Trever called me on it, I'm sharing the rant.  Please note, I am not an automotive engineer and I am strongly biased in my opinion.  It's also my blog - I don't have to be tactful, you can argue in the comments.  Do not cite me as authoritative, evaluate the arguments for yourself. 

A primer:  Anti-lock Brake Systems (hereafter "ABS") is a system put on vehicles which prevent the wheels from locking up or skidding.  It does this through a number of sensors which detect whether the wheels are moving relative to the other wheels of the car.  The precise way of doing it can vary from system to system.   Be wary - some vehicles with ABS (usually they are trucks) only function on the rear wheels, not all four wheels.  These vehicles will not react the same as ABS on passenger cars.

The reason ABS works is because of friction.  Maximum braking will happen when the friction on your brake pads is just a tiny bit less than the friction between your tires and the road.  Friction between your tires and the road changes frequently depending upon the conditions and it's hard to know that when you're driving - especially in an emergency.  When your brakes have too much friction, it releases your wheels until they find that perfect balance.

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I'm going to cite from a number of sources for your review.  The first is Transport Canada's Road Safety web page.  I consider it authoritative, balanced and fairly describing road conditions and hazards in Canada.  The second is from the National Highway Traffic Safety Administration so I can't be accused of being Canadi-centric, although I will primarily be discussing conditions I experience.  Canadian Driver has a brilliant article well worth reading.  I'll throw in a few others when a point needs to be raised.

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1.  When ABS first came out as standard equipment on passenger vehicles, it was marketed as a system that would assist you stop in much shorter distances to the point of being almost instantaneous.  That was misleading, deceptive advertising and it created much of the myth that ABS makes you safer all to itself.

Reality:  ABS will not reduce stopping distances at all unless you’re a piteously bad driver. ABS works by releasing your wheels briefly to prevent you from locking them up. The only scenario it will reduce your stopping distance is when you have your tires locked and you’re skidding along the pavement.  Sadly, I categorize the average driver as piteously bad.

The reason the claim is made that ABS will stop you more quickly MOST of the time is based on the assumption that the driver is using (or wants to use) all of the available braking power all of the time.  Good drivers think ahead of time and are looking ahead for hazards which may force them to brake.  Emergencies do happen, but they happen more often to drivers who drive at the edge of their vehicles capacity all the time.  Most of the time you are braking, you should not have your ABS engage at all.

A driver trained in threshold braking can match or improve stopping distances over a driver using ABS.  Remember that ABS will release the pressure on an individual tire's brakes momentarily.  It is counter-intuitive to think that turning your brakes off momentarily will slow you down faster.  It won't.  ABS equipped cars will always require more stopping distance until the circumstances are less than ideal.

The myth that ABS can only be outperformed in extraordinarily conditions persists.  The Insurance Institute for Highway Safety states "It is even possible on some surfaces to stop sooner without antilocks than with them, although such instances are rare."  Conventional braking systems can outperform ABS in many circumstances.

2.  ABS is a liability while driving in certain road conditions.

Fortunately, both governmental websites get this correct.  From the NHTSA, "On very soft surfaces, such as gravel or unpacked snow, ABS may actually lengthen stopping distances."  Transport Canada's webpage explains why.  Basically, when your tires are allowed to lock up, they will push the snow or gravel ahead of them, forming a burm.  Your tires often will get more traction in this condition.  This is less important for people who drive on plowed city streets, but can be critical for unplowed or gravel roads.

One point that was not mentioned is that the use of ABS encourages drivers to press the brake pedal to the floor all the time.  You are causing your tires to lock and you are counting on the technology in ABS to unlock them for you.  Let me state that again, you are told to "micro-skid" every time you hit your brakes.  This helps to polish our intersections in front of our stop signs to a glossy finish.  You're safer the first time, but after a hundred cars have went by they have made the circumstances more dangerous and more hazardous than they were before - at least until the next time the sanding truck comes through.

3.  ABS is not prescient.  Your brakes do not have any foresight into what you're about to experience while driving.

  My first experience with ABS was in a relative's brand new SUV.  My cousin was driving at the time, he came up to an icy intersection and wanted to test how the ABS would perform.  There were no other cars around us and he approached the intersection at an average speed and began braking with plenty of time to stop fully.  The wheels locked and we slid three quarters of the way through the intersection.  I was, of course, dismayed with the response which was repeated at the next intersection.  The SUV subsequently went into the shop at least three times to have the brakes examined.

The interview in Canadian Driver is the first time I've seen support for my anecdotal story.  Cpl. Eric Brewer is an RCMP officer that reconstructs collisions.  "Brewer tells the story of an ABS-equipped vehicle that slid through a stop sign and across a busy highway, barely missing the high-speed cross traffic. 'The driver was braking on pebbly, rolling gravel and then hit black ice on the pavement. The conditions fooled the ABS computer. You've got to be aware that, in those kinds of conditions, the ABS will not be able to stop the vehicle quickly.'ABS cannot think ahead for you, and the system will not necessarily respond as it is supposed to.  Drive with a margin of error to ensure your safety.

From Transport Canada, "Road hazards that will cause the ABS to function unexpectedly are gravel, sand, ice, snow, mud, railway tracks, potholes, manhole covers, and even road markings when it is raining."

4.  ABS will abstract the road feel from the driver.  This is a terrible thing for a drivers who have been taught Threshold braking and eliminates the ability to perform Cadence braking (or 'pumping the brakes').

Almost every driver in Canada was taught to pump the brakes on ice or slippery surfaces to stop quicker.  This is ingrained so hard that we still are generally tempted to pump the brakes on cars equipped with ABS.  With ABS you should not pump the brakes, ever.  Press firmly on the pedal and don't let up.  ABS does the cadence braking for you, more quickly than you ever can.  If you pump the brakes, you are turning off your ABS.

Unfortunately, when you press the pedal on an ABS-equipped vehicle, you can have any of a number of strange effects.

Far and away, the most common is a “grinding” sound and / or a pulsation of the brake pedal.

Most people think that something’s wrong when they first experience it. Many, many drivers do not like the pulsation and will actively release the brake pedal to prevent the sensation.  The grinding noise is perfectly normal, and the pulsation on the pedal is part of the brake system doing what it is designed to do.  From NHTSA:  "More specifically, ABS automatically changes the brake fluid pressure at each wheel to maintain optimum brake performance—just short of locking up the wheels. There is an electronic control unit that regulates the brake fluid pressure in response to changing road conditions or impending wheel lockup."

An attentive driver can feel the wheels lock through the feedback from the brake pedal.  The pulsation from ABS will mask that feedback entirely and you lose a critical clue as to your present driving environment.  Exceptional drivers can tell precisely which wheel has locked (locked front wheels have different characteristic feel than locked rear wheels - right and left is determined by which direction the car slides.)

If you can’t feel it, you can’t correct for it.

5.  Durability and long-term reliability

This is not going to be an issue if you get a new vehicle every three or four years. I drive a 26 year old car. A lot can go wrong with a car after 5 years, let alone 26.

The sensors for ABS are critical.  They can sometimes collect metallic dust or other impurities and stop working properly.  Moreso, you must have a well-functioning suspension system - including shocks, struts, and springs - to ensure your wheels stay on the road and don't bounce into the air throwing off the ability for ABS to function.

The extra maintenance involved will make your mechanic very happy.  ABS is one more system that needs to be checked and maintained regularly. You do not want a system that you’re dependent upon to stop you to fail unexpectedly.

Never forget that it is possible for a broken ABS system to become TOO sensitive. You may release the braking pressure from your wheels when your tires are not skidding and you have no need to engage your ABS system. This increases your stopping distance at all times and is a severe braking hazard.

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Nothing is all white or all black - unless you’re the New Zealand rugby team.

ABS gives two tremendous advantages:

1.  You can apply your brakes and steer at the same time.

In conventional brake systems, it’s not realistic to brake and steer together. Your wheels have a finite amount of traction to work with. This traction must be divided between the energy expended on braking and the energy expended on changing direction.

Finding the balance is difficult. If you run out of available traction, your front wheels will lock up. Remember this happens in a turn, so suddenly you’re skidding forward with your front wheels askew. It should go without saying, this is an extremely dangerous scenario to be in. Should you suddenly find traction (hitting a bare patch or slowing down enough that your front wheels suddenly “bite”) you will careen off in the direction your wheels were pointed in. Or suddenly roll the car if you’re driving horribly out of control.

An ABS system means you never have to try to find that balance - if your front tire locks, the ABS system will release it and continue to make maximum traction available to you for steering. With conventional brakes, you have to stay well within the limits of your traction. ABS gives you the ability to drive closer to the maximum limits of your traction.

I think this is what people refer to when they talk about ABS preventing loss of stability.  ABS prevents a vehicle from swinging side to side by balancing the braking on the left and right sides of the car.  If you're using Threshold braking or cadence braking (conventional brakes only, please!) you're only solution is in steering corrections which aren't a good option under braking.

2.  ABS prevents rear wheels from locking.

This is a marvelous thing, particularly in a vehicle such as a bus or a pickup truck.

It’s safer for the front wheels of a car to lock than the rear wheels. Most of the braking happens at the front brakes. When the front wheels lock up, the vehicle tends to “snowplow” - the nose dives, but the car slides more or less straight without veering left or right.

When the rear wheels lock, the vehicle tends to wildly swing to the left or the right - it wants to “swap ends.”

Think of your days on a bicycle.  Lock up the front wheel and you probably went over the handlebars.  Lock up the rear wheel and you skidded wildly in a fishtail.  Well, a car doesn't flip over very often, but it will fishtail when the rear brakes lock.

Buses and trucks are designed to carry varying weights in the back of the vehicle. Brake settings need to be firmer when they carry a full load, and softer when they are empty.  But we don't realistically want people changing their brake settings (you can do this on race cars, but you're probably not a race car driver) and ABS can mitigate the problem.  You can keep the brakes set to be more sensitive and let the ABS prevent them from locking and sending the truck into a fishtail.

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The bottom line?  Snow tires and better driver education will do much more than a technowizical gadget.

Get your vehicles out there and practice.  Don't believe that having ABS on your car makes you safer - you still have to be a safe, attentive driver.

Thank you for making it this far down the rant.  The line up to call me a moron starts...  Here:

Comments (2) -

2/1/2007 5:13:46 PM #

This is a topic on which I also have several opinions, and I do apologize for the lateness of my response, but how better to re-aquaint myself than to comment on a blog post of an old friend? Laughing
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<br>In reponse to this article, I'm not looking to refute any of the evidence that you've supplied related to ABS. I believe it is all factual and true, but, you're belief that ABS is unnecessary colors all of your statements around this topic in an incorrectly negative light. I'll address your points to hopefully make my counterclaims as clear as possible. &nbsp;One thing in general though that I find about the article (rant) is that critizism of the technology seems to be confused with critizism of the marketing of ABS to the general consumer.
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<br>1. &nbsp;When ABS first came out as standard equipment on passenger vehicles, it was marketed as a system that would assist you stop in much shorter distances to the point of being almost instantaneous. &nbsp;That was misleading, deceptive advertising and it created much of the myth that ABS makes you safer all to itself.
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<br>Reponse: Generally speaking, in the bad road conditions that the vast majority of drivers (piteously bad) will encounter, ABS can shorten the stopping distance, but this is not the main purpose of ABS and as such, the marketing, not the technology, was misleading. As per the AAA:
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<br>Under most conditions, a vehicle with a good anti-lock brake system can stop in a slightly shorter distance than an average driver could accomplish in the same vehicle without ABS; however, that is not the main purpose of ABS, and the difference is generally not great enough to notice or be of any real use. ABS certainly doesn't improve your stopping distance nearly enough to justify driving faster or following more closely!
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<br>Please follow the link for the full response as it does include other information, including when ABS can increase stopping distance.
<br>(<a rel="nofollow" target="_new" href="www.aaafoundation.org/.../index.cfm://www.aaafoundation.org/.../a>;)
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<br>To sum it up, ABS in the hands of a user who understand the system can provide a safer driving experience.
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<br>2) ABS is a liability while driving in certain road conditions.
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<br>Again, I think that attacking the technology of ABS vs. the users expectations (perhaps misguided) and ABSs' lack of performance against those expectations may create this sentiment.
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<br>As stated above, ABS does not necessarily decrease stopping distances in some conditions. Calling it a liability is, imho, inaccurate. ABS will always provide more steering control in the hands of a educated user, if not the perceived benefit of shorter stopping distances.
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<br>3) ABS is not prescient. &nbsp;Your brakes do not have any foresight into what you're about to experience while driving.
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<br>No driving system is prescient. The most important system in any vehicle is the human being sitting in the driver seat guiding 2 tonnes of metal down the road. Again, blaming the technology for failing to allow drivers to be completely ignorant of their role in guiding the vehicle down the road is misguided.
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<br>ABS only takes control when the system detects that wheels are locking up. It doesn't automatically avoid potholes. It doesn't stop you from following to close. It doesn't make you slow down in really bad weather conditions. It does this because locked wheels increase stopping distances (99.999% of the time) and removes a drivers ability to steer the car (all the time). &nbsp;And because it addresses these two problems, cars are potentially safer to drive due to ABS being installed. They are not guaranteed to be safer because idiots can confound any technology that is put in place to make them less dangerous to society.
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<br>4) ABS will abstract the road feel from the driver.
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<br>ABS does not abstract road feel. With ABS, you will still feel a pump, a rut, crack, squirrel, or weird road surfaces. I would suggest that we do not feel wheels lock up with our feet, we detect it with our other senses. (ears mostly, but our sense of motion and brain help an awful lot.)
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<br>ABS will require you to rethink how you brake in specific situations. As stated, you can no longer Threshold brake effectively because ABS is trying to do it for you and the competition between the driver and the ABS system diminishes the effect of both. You can still try to Threshold Brake, but it feels really weird. Again, education and experience will resolve this conflict and leave the road with a potentially safer driver/vehicle combination.
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<br>5) Durability and long-term reliability
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<br>ABS systems, as far as I know, are extremely sensitive to problems within the system, and that is why the little yellow light on the dashboard lights up telling you that your ABS system has been deactivated due to a problem and you will have to brake without any ABS assistance.
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<br>ABS does not increase brake pad or tire wear (It actually would decrease tire wear. Skidding eats rubber for lunch.)
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<br>Yes, ABS systems, when they fail, will be significantly more expensive to repair than a non-ABS system. This is true of any technology enhancement that we do in our lives. If your fuel injection system dies, it will be expensive. When your 4wd system dies, it will be more expensive than the 2wd system. When your high end computer dies, it will probably be more expensive than a low end entry system that lacks all of the bells and whistles. But one key aspect of ABS systems is that when they fail, the braking system must be able to work as if there was no ABS. This is a government requirement for safety so that when an ABS sensor fails, a person can still drive as safetly as the vehicle will permit.
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<br>The maintenance costs of technologies should factor in to a persons initial purchase and not be factored in as a negative against the technology. I would go against this a bit if the technology provided so much safety and the price was prohibitively high that no one could use it.
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<br>Those are my thoughts on the first 5 points. I won't address the positives because I aggree with them, except for the statement about the effects a locked wheel has on a car.
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<br>All vehicles tend to &quot;swing around&quot; a locked wheel and drag it behind them. If a rear wheel locks, it will be &quot;dragged&quot; behind the momentum of the vehicle causing the vehicle to seem to continue pointing straight ahead. &nbsp;If a front wheel locks up, the vehicle will attempt to &quot;drag&quot; the wheel behind while the rest of the car continues to try and speed along, causing the car to look like it is swinging the back around to the front.
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<br>I've had this demonstrated to myself on small models and in an actual test-bed vehicle with a braking situation simulation system installed.
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<br>So, to sum it up, ABS is a great technology that allows vehicles the potential to be much safer on the roads. It does not make idiots smart people (or look like smart people) and it should be used by an educated driver to maximize the benefit. And we should all be educated about the tools that we use. I wouldn't set someone lose on a computer with business critical systems on it without training, and arguably, setting someone lose in a car without proper training is a greater hazard to society.
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<br>Cheers,
<br>Dave
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He who ran a voice BBS with you once, long ago. :D |

2/1/2007 11:03:35 PM #

Daaaaaaaaaaaaaaaaave! &nbsp;You're not going to believe this, but I was talking about you only yesterday. &nbsp;We got a new printer at work and we were talking about your laser printer - the first one I'd ever seen.
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<br>Great to see you! &nbsp;What's been happening?
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<br>And, you'll forgive me, but you're completely and utterly wrong. &nbsp;:-D &nbsp;(I did mention I love an ABS scrap, right?)
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<br>---
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<br>1. &nbsp;Under most conditions, a vehicle with a good anti-lock brake system can stop in a slightly shorter distance than an average driver could accomplish in the same vehicle without ABS; however, that is not the main purpose of ABS, and the difference is generally not great enough to notice or be of any real use. ABS certainly doesn't improve your stopping distance nearly enough to justify driving faster or following more closely!<br>
<br>Well, there the AAA is talking about altering your driving style. &nbsp;You're not safer to drive faster or follow closer with ABS. &nbsp;They're right. &nbsp;But I am not discussing driver ability here - no "average driver can stop sooner or later" argument.
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<br>Strictly speaking, technologically, ABS is the system that releases the wheel from locking. &nbsp;When the wheel has been released, it does not have functional braking for that split second. &nbsp;Time a wheel is not braking only adds braking distance. &nbsp;Separating out driver ability, a car with active ABS will take longer to stop.
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<br>Marketing lied. &nbsp;Marketing is propaganda, and it hides or skews the truth. &nbsp;It's been said so long, people buy into it without being critical.
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<br>2. &nbsp;"As stated above, ABS does not necessarily decrease stopping distances in some conditions. Calling it a liability is, imho, inaccurate. ABS will always provide more steering control in the hands of a educated user, if not the perceived benefit of shorter stopping distances."
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<br>I would much rather have my tires dig in beneath the level of snow to grip the pavement below if they can. &nbsp;The point was made to disprove that ABS is better all the time in all conditions. &nbsp;It isn't. &nbsp;Sometimes it's better to go without.
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<br>3. &nbsp;"No driving system is prescient. The most important system in any vehicle is the human being sitting in the driver seat guiding 2 tonnes of metal down the road. Again, blaming the technology for failing to allow drivers to be completely ignorant of their role in guiding the vehicle down the road is misguided.
<br>
<br>ABS only takes control when the system detects that wheels are locking up. It doesn't automatically avoid potholes. It doesn't stop you from following to close. It doesn't make you slow down in really bad weather conditions. It does this because locked wheels increase stopping distances (99.999% of the time) and removes a drivers ability to steer the car (all the time). &nbsp;And because it addresses these two problems, cars are potentially safer to drive due to ABS being installed. They are not guaranteed to be safer because idiots can confound any technology that is put in place to make them less dangerous to society. "
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<br>I do not blame the technology for failing - I blame the drivers for thinking technology will bail them out of an emergency situation. &nbsp;Avoid getting yourself into trouble in the first place!
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<br>ABS only activate when the driver has miscalculated and has placed him or herself into a dangerous situation. &nbsp;I won't allow anyone to quote 99.999% of the time - show me proven stats. &nbsp;Prove to me that it applies to MY driving throughout the year. &nbsp;Demonstrate that you are aware of the situations in which I drive and the relevance of ABS to my driving style and habits. &nbsp;ABS can be a liability and I will not accept claims that I am 99.999% safer with them. &nbsp;Furthermore, they do not give me the ability to steer all the time - ABS only comes into play when activated. &nbsp;Most of the time, I'm not locking my brakes. &nbsp;When ABS activates on my car, I'm looking to stop, not to steer.
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<br>4. &nbsp;"ABS does not abstract road feel. With ABS, you will still feel a pump, a rut, crack, squirrel, or weird road surfaces. I would suggest that we do not feel wheels lock up with our feet, we detect it with our other senses. (ears mostly, but our sense of motion and brain help an awful lot.) "
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<br>Say WHAT?
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<br>When ABS activates, I get a pulsation in my brake pedal. &nbsp;I can no longer feel slippage through the pedal. &nbsp;Yes, I can feel with my bum, I can listen to the gravel grinding beneath my wheels, but it is through resistance in my brake pedal that I get feedback that tells me how hard I should press.
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<br>5. &nbsp;"ABS does not increase brake pad or tire wear (It actually would decrease tire wear. Skidding eats rubber for lunch.) "
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<br>Great point. &nbsp;ABS can potentially save rubber on dry pavement. &nbsp;Why anyone should ever skid on dry pavement escapes me, but reduced tire wear is a very good notion that I completely forgot about. &nbsp;Tack that on as another positive.
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<br>The extra cost in maintenance would be okay if I got to choose whether I wanted ABS or not. &nbsp;In the Murano, I don't get the choice. &nbsp;It's becoming less and less prevalent to have vehicles without ABS. &nbsp;I wouldn't mind nearly as badly if I could be assured that ABS was significantly better. &nbsp;Instead I argue that ABS is a detriment that I have to pay more for in the first place, and pay more in continued maintenance on an ongoing basis.
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<br>For a vehicle swinging around, well, my best suggestion is to try it on a bicycle. &nbsp;If you manage to keep your weight on a straight axis you won't observe it. &nbsp;You'll simply come to a stop more or less facing in the same direction.
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<br>If you skid your back wheel and let your body sway, the back wheel will de-stabilize and you'll swing left and right like a pendulum. &nbsp;If (and KEEP YOUR WEIGHT BACK ON THE BIKE SO YOU DON'T GO OVER THE HANDLEBARS!) you skid your front tire, you will plow to a stop and you will be much less likely to become unstable.
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<br>There's a great experiment you can do if you have a toy car with accessible axles. &nbsp;Tie a string to the axle so it will have to skid when it runs out of line. &nbsp;Tie it to the back axle, it will swap ends. &nbsp;Tie it to the front axle, it snowplows to a stop. &nbsp;It's the reason cars have more stopping bias towards the front tires instead of the rear. &nbsp;Helps keep them stable, and most of the braking occurs on the front wheels, not the back. &nbsp;Maybe I'll have to rummage through my son's toy box and see if he's got something in there.
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<br>My summation: &nbsp;ABS is costly and mostly ineffective. &nbsp;It's only activated in emergencies the driver should not have been involved with in the first place. &nbsp;I agree with the idea we'll get a whole lot safer out there only with much better training and education of the driving public.
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Mark Zaugg |

Comments are closed

Welcome

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