What is Antilock Braking System or ABS in cars?

 | 4 minutes read

Antilock Braking System (ABS): Construction And Working

Antilock Braking System (ABS) is a type of active safety system of a vehicle. It is also known as the anti-skid braking system. This system comes into action when the driver suddenly applies the brakes during an emergency. Employing the antilock braking system on cars and bikes is now mandatory in most parts of the world.

The need for Anti-lock Brakes:

Whenever the driver suddenly applies the brakes to a high-speed vehicle, there is always a chance of the 'wheel-lock'. The wheel-lock means that the respective wheel stops suddenly instead of coming to a halt slowly. Due to the wheel-lock, the driver loses control over the vehicle and the vehicle skids off the road. Thus, a fatal accident takes place. In order to avoid such situations, the manufacturers employ the ABS system.


The ABS has the following components:

  1. Wheel speed sensors
  2. ABS control module
  3. Brake control unit
  4. Valves
  5. Pump
components of Antilock Braking System (ABS)
Components of Antilock Braking System (ABS) and its normal operation

Wheel speed sensors continuously monitor the speed of each wheel. As long as all the wheels have comparable speed, the system does not interfere with their operation. However, if the speed sensors find that the speed of any of the wheels is reducing drastically, then it means that the particular wheel is going to lock.

However, the locked wheel hampers vehicle stability. Thus, the vehicle stops responding to the steering input given by the driver. At this moment, the vehicle also starts to skid; thereby causing a fatal accident. To avoid such a mishap, the ABS comes into action.

ABS detects a problem
This is how the ABS detects a problem

How does the ABS work?

After receiving the signal of very low speed from the wheel speed sensor, ABS module orders the brake control unit to reduce the braking force of that wheel. Reducing the braking force means reducing the hydraulic pressure in the brake line acting on that wheel. The Brake Control Unit reduces the line pressure with the help of valves in the system. When the braking force reduces, the wheel starts rotating at a higher speed; thereby avoiding the wheel-lock. As the wheel doesn't lock, steerability of the vehicle remains intact. This means that the vehicle moves according to the driver's input without skidding. Once the normal condition is restored, the Brake Control Unit restores the hydraulic pressure in the brake line with the help of a pump.

This is how ABS takes corrective action


  1. ABS maintains the vehicle steerability and stability during panic braking.
  2. It reduces the braking distance by up to 10% or more, especially on wet surfaces.
Better steering control with Antilock Braking System
Better steering control with Antilock Braking System (Courtesy- Toyota Motor Corporation Australia)


Perhaps the only disadvantage of the Antilock Braking System is its higher cost. In recent times, purchasing the Antilock Braking System installed bike or car costed significantly to the customer. However, this higher cost is completely offset by the improved safety this system provides. Also, the auto industry is working on developing a low-cost version of the antilock braking system.

Classification of ABS:

Based on the number of speed sensors and valves, The Antilock Braking System is of following types:

Sr. No. Type of ABS Description
1 Four channel-four sensor ABS Each wheel has a separate valve and sensor
2 Three channel-four sensor ABS (i) A separate sensor for each wheel.

(ii) Separate valves for front wheels.

(iii) Rear wheels controlled by only one valve.

3 Three channel- three sensor ABS (i) A valve and a sensor each for front wheels.

(ii) One valve and one sensor for rear wheels.

The driver may feel pulsations in the brake pedal when the antilock braking system activates. However, it depends on the severity of the braking condition. This is absolutely normal and care is to be taken not to release the brake pedal during this phase as it will prevent the system from working properly.

Motorcycle ABS:

Motorcycle ABS is a small-scale version of a car ABS. However, its working is exactly similar to that of full-scale car version. However, it requires less number of valves and wheel speed sensors due to the presence of only two wheels.

According to Bosch, using motorcycle ABS increases the stability of the bike and improves riding comfort. The company has also proved that the braking distance reduces considerably when the bike uses the anti-lock braking system.

Watch Antilock Braking System in action:

Read more: Electronic Brakeforce Distribution (EBD)>>

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