Disc Brakes: Basics, Components, Advantages & Disadvantages

In a disc brake, calipers are squeezed against the rotating disc to generate friction and reduce the motion of a vehicle.

Disc Brakes

A disc brake is a type of braking system that uses calipers to squeeze pairs of brake pads against the rotor/disc to create friction and reduce the motion of the vehicle or completely stop it. When braking action occurs the kinetic energy is directly converted into heat energy and heat is directly dissipated into the atmosphere.

The disc braking system works on the principle of pascal’s law according to which “the confined liquid transmits pressure without loss equally in all directions.

In a disc brake system, energy is transferred from the pedal to the brakes. It is also a type of hydraulic brake system as some applications include the use of hydraulic pressure of brake fluid and some are without the use of hydraulic pressure which is mostly seen on bicycles and mountain bikes.

Main Parts of Disc Braking System

Disc Brake
Main Parts of Disc Brake

The main parts of disc braking systems are as follows:

Brake Disc or Rotor

It is the part that rotates along the wheels and is attached to the rim of the wheel. The brake disc is squeezed with the help of brake pads to create friction. It is the part that produces a lot of heat. Some rotors have holes drilled in them to dissipate heat directly to the environment thereby reducing its weight.

Brake Pads

They are hard material that squeezes the disc rotor to create friction. They are attached to the pistons which are housed inside the caliper. Brake pads are usually made up of hard rubbers, ceramics, semi-metallic materials, etc.

Brake Fluid (if equipped)

The brake fluid is used to create hydraulic pressure which is then used to force the piston outwards towards the disc rotor. They have a high boiling point to sustain high temperatures, are chemically stable, and have lubricating properties.

Fluid Reservoir

A tank or reservoir where the brake fluid is stored.

Disc Brakes Assemblies

Wheel Hub Assembly

It is the assembly that holds the wheel and the disc rotor and bearing inside it which provides it for smooth operation.

Caliper Assembly

It is the assembly that holds the brake pads and pistons. Caliper assembly consists of rubber bellows (for dust protectection), inner and outer brake pads, the main caliper frame, and bracket. It has the inner flow line through which the brake fluid flows throughout reaching the piston. They are of two types: fixed calipers (calipers that cannot move) and floating calipers (movable or sliding calipers).

Master Cylinder Assembly

It is the main part of the system. There is a push rod, outlet ports, and fluid reserve outside the master cylinder. Inside the master cylinder, there are inlet ports, compensating port, piston seals, primary piston, secondary piston, and retaining springs. This portion is near the brake pedal. It might not be present in some small applications.

Working of Disc brake

When the brake is applied or the brake pedal is pressed the hydraulic pressure is applied to the fluid inlet tube, due to which the hydraulic pressure reaches the cylinder piston inside the calipers. This hydraulic pressure then forces the piston to move outwards the caliper and towards the rotor.

Brake pads that are attached to the piston come into surface contact with the rotor disc and then due to friction, the speed of rotation of the wheel reduces.

As soon as the brake pedal is released the return springs quickly force the master cylinder piston to come into its original rest position. The caliper piston also comes in its original position. The surface contact between the brake pad and the rotor disc is now over and the fluid in the inlet lines returns slowly.

Applications

  1. Higher cc performance bikes as their speed are more there is a need for better stopping power. They are also found in commuter bikes.
  2. All modern cars are equipped with disc brakes.
  3. Bicycles and mountain bikes.

Advantages

  1. It has a higher mechanical advantage.
  2. It has better stopping power due to hydraulic pressure when compared with drum brakes.
  3. The heat-resistant capability of the disc rotor is more. Also, the cooling rate is faster due to better heat dissipation.
  4. Maintenance is easier.

Disadvantages

  1. They are heavier as the whole system includes caliper assembly, rotors, brake fluid, and master cylinder assembly. They add up more weight.
  2. Brake pad replacement is more involved in a disc brake.
  3. The disc brake system also adds the cost of brake fluid.

Preference of Disc brake over Drum brakes

The disc braking system is generally preferred over drum brakes if cost is not a matter of concern. The reasons are:

  • Disc brakes offer more stopping power and less stopping distance than drum brakes due to their mechanical advantages. However, they are less efficient than air brakes.
  • Disc brakes are self-adjusting on their own whereas drum brakes need to be adjusted over a period of time. There are some self-adjusting drums but they have too many disadvantages like high complexity, taking more space, and weight constraints.
  • Generally wearing part of the disc braking system is the brake pads, they can be replaced in a couple of minutes. But in the case of drum brakes, the whole system is integrated inside the drum, and the wearing parts are more like brake lining and brake shoes. Mostly, the drum brake wears due to hard braking over time with less effect and due to thermal expansion.

Drum Brakes v/s Disc Brakes

  1. In the case of disc brakes, Heat dissipation is better than that of drum brakes as heat-producing parts like the rotor contain drilled holes and is open that maximize cooling. As the whole mechanism is contained inside a drum, the drum brakes dissipate less heat than disc brakes.
  2. Disc brakes don’t produce scratching sounds when under contact with water. Whereas, Drum brakes produce that sound and also become less efficient when in contact with water like during the rainy season. Water enters inside the drum during rains.
  3. Drum brakes have non-linear characteristics as the braking force is not directly proportional to the force applied. Disc brakes have linear characteristics as the flat surface (brake pads) is rubbed against the flat surface (disc rotor surface).
  4. If cost is a factor, then drum brakes are used instead of disc brakes. This is the reason why we see entry-level motorcycles (50cc-100cc) are seen with drum brakes on both wheels. They are also offered a front disc brake and rear drum brake to keep the price low.

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