How Does ABS Work?

It’s common every-day technology, but often misunderstood.

byPeter Nelson|
abs bmw m340i brakes braking
Peter Nelson


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One of the most accepted-as-everyday developments in new-car technology is ABS, or a car's anti-lock braking system. It's been around since the '90s, though wasn't considered mandatory equipment on new cars by the National Highway Traffic Safety Administration (NHTSA) until 2012. Which seems odd, because again, didn't we all think it was pretty normal stuff for far longer than that?

And while we've explained what ABS is before—the name says it all—there's more to it. Especially in regard to the finer details of how it functions, and what its true benefits are. Let's discuss and potentially dispel some misinformation and get learned.

The Basics of How ABS Works

On a macro scale, ABS hops into action during braking to avoid locking the brake calipers onto the brake rotors, creating a skid, throwing traction out the window, and thus losing control of the vehicle. That last bit is the most crucial, as losing control isn't usually considered a good thing to most people.

The ABS system does this by automatically pumping the brakes and allowing the wheel to come to a stop in a more controlled manner. Instead of locking up, it quickly applies, releases, and reapplies the brake pads until the car comes to a stop. By doing this, the system helps maintain traction across the tire tread and disperses heat more efficiently. This means more control for the driver, whether heading in a straight line or while braking with the wheel turned.

Contrary to popular belief, ABS doesn't automatically mean shorter stopping distances. It helps maintain control, not specifically shorten stopping distances. Though, cars with ABS do indeed almost always stop shorter. It also has other strong secondary benefits like helping to prevent warped rotors and flat-spotted tires.

Sidenote: if you've ever seen someone slam on their brakes to avoid blowing a red light, and their wheels just screech away with reckless abandon, either their ABS isn't working or it isn't equipped. And those folks will now have the joy and the pleasure of shelling out for two to four new tires to rid those nasty flat spots. Always be sure to look well ahead, folks.

Peter Nelson

The Science of How ABS Works

The way ABS works is a generally simple concept, as there only a few components in the system, with those being the ABS computer (or module), the ABS pump (also known as a block), wheel speed sensors, and the conventional braking system of the master cylinder, brake lines, and caliper/rotor combo right near where the rubber hits the road.

When a heavy braking situation is identified by wheel speed sensors, as well as potentially other sensors that assist in gathering info, the ABS computer triggers the pump to come alive and actuate the process of opening and closing a series of valves. In the hierarchy of brake function, the pump is situated right after the master cylinder, which provides the flow of fluid to actuate the brakes. The ABS pump's valve actuation translates down the hardlines to the soft lines in the wheel well, where it rapidly clamps and unclamps the caliper's brake pad against the rotor. It ceases when the driver releases the brake pedal.

The key is to let ABS do its thing, as when you feel a weird pulsing in the pedal and potentially hear some odd mechanical noises, that's normal. If you lift too early, the system cuts off. Depending on the scenario, this might be very bad.

ABS works best in both wet and dry road conditions, though the best plan of attack while rolling over snow and ice is to drive carefully and modulate the brakes with more precision yourself. Not to mimic ABS, but rather to ensure you don't overwhelm the tires. They must have as much grip as they can muster. For the best possible control over snow and ice, nothing beats a good set of snow tires.

Other Benefits of How ABS Works

In non-emergency situations, technology has helped expand ABS systems' functions. It's in many modern cars' off-road traction control systems, such as Land Rover's Terrain Response, by precisely actuating the brakes independently at all four corners to maintain as much grip and contact patch on off-road surfaces as possible. It also comes in handy in motorsports, where the boost in braking control translates to faster lap times, safer racing, and less wear on brakes and tires.

Even in non-motorsports enthusiastic driving, ABS often mimics a limited-slip differential to try and send power to the wheel or wheels with the most traction. Though, the execution isn't always (in fact, depending on who you ask, is never) as good as an actual limited-slip differential.

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