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 Do not cite me as authoritative, evaluate the arguments for yourself.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.
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.
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.
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.
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: