Antilock Brake Systems (ABS)|
Wheel lockup: slippery when wet.
When your wheels lock up on wet and slippery roads or during a panic stop, you may lose traction and control, causing your vehicle to spin. Antilock brakes keep your wheels from locking up, so your car maintains directional control around hazards if you can't make a complete stop in time.
The pumping heart of an antilock brake system.
ABS works with your regular braking system by automatically pumping them. In vehicles not equipped with ABS, the driver has to manually pump the brakes to prevent wheel lockup. In vehicles equipped with ABS, your foot should remain firmly planted on the brake pedal, while ABS pumps the brakes for you so you can concentrate on steering to safety.
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.
How to know if your vehicle is equipped with ABS.
Most newer vehicles offer ABS as either standard or optional equipment. To find out whether your car has an antilock brake system, and what type, read your owner's manual. You can also check your instrument panel for a yellow ABS indicator light after you turn on the ignition. And when you buy, lease or rent a vehicle, always ask if it comes equipped with ABS.
There's more than one kind of antilock brake system.
Four-wheel systems, including those found on cars and minivans, are designed to keep all four wheels from locking up. Rear-wheel-only systems, found on some pickups, vans and sport-utility vehicles, keep the vehicle from spinning out of control, but the front wheels may lock up, resulting in a loss of steering control.
The feel and sound of ABS.
When ABS is activated, you may experience a slight vibration or a rapid pulsation of the brake pedal—almost as if the brakes are pushing back at you. At times, you will feel the pedal suddenly drop. The valves in the ABS unit may make a grinding, scraping or buzzing noise. This means your ABS is working. Continue to apply firm pressure and steer. Do not take your foot off the brake pedal.
Do cars with ABS stop more quickly than cars without?
Perhaps, but that's not the main purpose of ABS. It is a system designed to help you maintain control of the vehicle during emergency braking situations, not necessarily make the car stop more quickly. ABS may shorten stopping distances on wet or slippery roads and most systems may shorten stopping distances on dry roads. On very soft surfaces, such as gravel or unpacked snow, ABS may actually lengthen stopping distances. In wet or icy conditions, you should still make sure you drive carefully, always keep a safe distance behind the vehicle in front of you, and maintain a speed consistent with the road conditions.
Stop and get to know your ABS.
After you consult your owner's manual for more details, give your ABS a mini-road test. In an unobstructed parking lot, drive your vehicle at a speed above which the antilock brake system activates (usually above 10 mph) and apply the brakes firmly. The antilock brake system is speed-sensitive and will not activate at very slow speeds. Also, it's easier to activate ABS on a wet and slippery surface. The antilock system should prevent the wheels from skidding. Practice NOT pumping the brake.
Other considerations for better braking.
How effectively you can stop your vehicle can be influenced by many factors including:
| ||Road conditions, since wet and slippery roads provide less tire friction and will therefore result in longer stopping distances than dry roads.|
| ||Vehicle condition, including properly inflated tires that have good tread, and a properly maintained brake system that is free from defects such as worn linings, air or dirt in the brake fluid, or leaks that reduce the available braking force.|
| ||Driver reaction time. At 60 mph, your car travels 88 feet each second. Reaction time, that is the time it takes a driver to identify a braking situation and then apply the brakes, will affect the overall distance to stop. A one-half second reaction time will result in a vehicle stopping 88 feet shorter from 60 mph than a one-and-one-half second reaction time. That is why it is important to always pay attention to the road and other traffic.|
| ||Type of brake system. When faced with a panic braking situation, ABS allows a driver to rapidly apply the brakes without worrying about wheel lockup, and the vehicle begins to stop immediately. Without ABS, a rapid, hard brake application could cause wheel lockup and loss of vehicle steering control, if the driver does not pump the brakes correctly or limit the brake pedal force to prevent wheel lockup. Therefore, more driver skill is needed to obtain short stops without ABS.|
Be the safest driver you can be. Call or log on for more information.
Call the NHTSA Auto Safety Hotline at 1-888-DASH-2-DOT (327-4236), TDD 1-800-424-9153 or find more information on NHTSA's web site at www.nhtsa.dot.gov.