Disc brakes have advantages on all sides over drum brakes. But why do vehicles still use drum brakes at the rear?
Keep in mind, 60 - 80% of the braking force will focus on the front wheels. In other words, the front wheels have a greater burden to stop vehicle when braking.
Therefore, disc brakes become a choice to used on the front wheels in every vehicle.
But what is the reason the disc brake use in the front brake ?
1. Good Heat Rejection
Disc brake has an open construction, 90% of the disc surface contacted with fresh air. Therefore, the heat generated from the braking process will be transferred to the air directly.
Overheating of the brake system causes brake system failure. The brake pads may harden when exposed to overheating, resulting in poor brakes performance.
The use of disc brakes at the front makes the brake system failure is less due to a more stable brake disc temperature.
2. Water resistance
When the disc brake is exposed to water, it will not interfere with its performance. Because the water attached to the disc will immediately bounce out due to the effect of the centrifugal force generated when the disc rotates.
While on drum brakes, when exposed to water, water will enter the drum brake and it difficult to get out. So that it can interfere with the braking performance.
3. More optimal when combined with ABS
ABS works by modulating braking pressure. So when the driver depresses the brake pedal, the brake pads must clamp the disc. However the ABS, the clamp of brake pads will come off automatically when the wheel locked. And the brake pad clamp will return automatically when the wheel has free.
The process took place at very fast intervals (under 1 second).
The travel distance of brake pads to apply the brakes is very small (in millimeters). That makes ABS brakes easier to modulate the brake pads.
From the three reasons above, we know that disc brakes have a significant advantage than drum brakes. But why, many vehicles still use drum brakes at the rear?
1. Drum brake has better locking ability
Disc brakes are more responsive when than drum brakes to stop the vehicle, which means that the disc brakes will stop the vehicle faster.
But in order to keep the braking, the driver must hold the brake pedal with high tension. While the drum brakes have a better locking ability, even though the drum brakes can not stop the vehicle faster, the drum brake is better to lock the wheels due to its construction.
This wheel lock ability is very necessary for the parking brake.
Therefore, drum brakes are used at the rear because drum brake has the main job as a parking brake that hold the vehicle when it is not moving.
2. Drum brakes can be activated without a hydraulic system
Drum brakes have two inputs, the first is the brake pedal which is the main input of the brake system. The brake pedal uses a hydraulic system for front and rear brake. This means that both disc and drum brakes are controlled by a brake pedal.
But the drum brake has a second input, it is the parking brake lever.
The parking brake lever works mechanically without going through the hydraulic system.
But this can be an alternative brake when there are hydraulic system failures.
Therefore, even though drum brakes are obsolete, they are still very useful in vehicles manufactured today.