The Mechanics of Anti-Lock Brake Systems

Natalie Josef
March 9, 2011

When I was seventeen years old, I was driving in Virginia on a cold winter day. Though it wasn't snowing at the time, there was ice and snow on the road. People were generally moving the speed limit, which was about 55mph.

In the car with me was my best friend, Jan. We were following her parents, on our way to a weekend getaway. Everything was going well ... until a sea of red brake lights suddenly appeared before me. I had no choice but to slam on the brakes, something I had never done before in my short driving career.

I expected us to crash, or at the very least skid out of control (Jan's screaming indicated she expected a fiery, brutal death), but to my amazement, I was able to keep the steering wheel straight and maintain control of the vehicle.

When we finally came to a stop, we both looked at each other and kind of laughed and cried at the same time. We couldn't believe we were okay.

At that time, I thought my superb driving skills and excellent decision-making abilities were what saved the day. I was seventeen after all. But the real reason we were spared that day? Anti-lock brakes (ABS).


ABS has been available on cars in the U.S. since 1978. Their purpose is to prevent the wheels from locking up or skidding during braking. If the brakes lock up, the vehicle takes longer to stop and the ability to steer the vehicle is greatly diminished.

The ABS system prevents wheel lock-up by monitoring each wheel with a wheel speed sensor. When the wheel starts to skid, hydraulic pressure to the wheel brake is temporarily reduced to prevent the wheel from skidding.

In a panic situation, our first inclination is to firmly plant our foot on the brake—luckily, this is exactly what we are supposed to do. Some vehicles even come with "brake assist," which actually applies the brakes for you. ABS helps us keep control of the vehicle and helps us steer around danger instead of skidding into it.

For more information on ABS systems, click here >>


Natalie Josef

About the Author

Natalie Josef is an automotive expert at RepairPal, the leading online source of auto repair resources and estimates. With many ASE Master certified mechanics on staff who have decades of experience, RepairPal knows all the fine points of car repair.

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