Brakes - what are front discs and rear drums?

When truckers buy a truck, they can always hear the salesperson's introduction: This one uses a front disc and rear drum design, so what does this mean?

The so-called front disc and rear drum refers to the use of disc brakes on the front wheels of the vehicle and drum brakes on the rear wheels. Why do different wheels of the same vehicle use different braking methods? This requires an understanding of the characteristics of these two types of brakes.

The disc brake is controlled by hydraulic pressure. The main parts include brake disc, wheel cylinder, brake caliper, oil pipe, etc. The brake disc is fixed on the wheel and rotates with the wheel, and the wheel cylinder is fixed on the bottom plate of the brake and the brake caliper. The two friction pads are installed on both sides of the brake disc.

Advantages of Disc Brakes

Quick response

According to relevant information reports, if the three-axle tractor chooses full disc braking, the braking distance can be reduced by about 30%, that is, when emergency braking at a speed of 60km/h, the braking distance can be shortened by about 10 meters. It also has a relatively good performance in reducing the dead weight of the vehicle. Compared with the use of drum brakes, the dead weight of the vehicle can basically be reduced by about 250 kg.

More comfortable

Relevant data shows that when using drum brakes, the difference in braking force between the left and right wheels is as high as 30%, while when using disc brakes, because of the self-adjusting function, the difference is within 10%, which can improve the driving comfort of the vehicle.

Good thermal stability

Disc brakes are less affected by frictional resistance, and in general, the specifications of its brake friction lining are not very large, and the working surface layer is only about 6% to 12% of the total area of the brake disc, so the impact of disc brakes on the braking effect after thermal expansion is relatively small.

High reliability in contact with water

When the disc brake is braking, the pressure between the brake disc and the brake pad is relatively large, and the high-speed rotating brake disc will have a large centrifugal force. Under the action of the brake, the water between the brake disc and the brake block is easily squeezed out, so the reliability of the disc brake in contact with water is relatively high.

Better heat dissipation

Disc brakes usually adopt a ventilated disc structure, which has a large surface area for heat dissipation and is installed in an exposed position. While the wheels are rotating at high speed, the air circulation in this position is accelerated, so that it achieves a better heat dissipation effect.

Disadvantages of disc brakes

Low adaptability to working conditions

Due to its structure, the strength of disc brakes is not high, which limits the use environment and transportation conditions of disc brakes and is not suitable for extreme transportation environments such as heavy loads.

Smaller Heat Tolerance

Compared to drum brakes, disc brakes have a smaller disc area, which results in a smaller heat capacity. With the same braking effort, the heat generated by a disc brake is greater than that of a drum brake.

Drum brake consists of a brake drum, brake shoes, brake sub-pump, friction pads, return spring. When braking, the brake shoes rotate outward under the action of the actuating device, and the friction pads on the outer surface press against the inner cylindrical surface of the brake drum to produce a braking friction torque on the drum.

Advantages of Drum Brakes

Strong braking force

When drum brakes are in operation, the brake shoes will be squeezed outward due to expansion, pressing the brake shoes tightly against the brake drum and causing friction to achieve the braking effect. Compared with disc brakes, they do not need to rely on the assistance of a vacuum-assisted device to produce sufficient braking force.

Disadvantages of drum brakes

Decrease in braking efficiency

The drum brake is in a closed space, so its heat dissipation will not be very good, and will gather a lot of heat in the braking process, making the brake shoes and hubs deformed under the influence of high temperature, thus causing brake recession and shaking, resulting in a decrease in braking efficiency.

Slow Braking Response

Drum brakes use a variety of components, so their structure is more complex and their braking response is slower than that of disc brakes.

The comparison of disc brakes and drum brakes shows that there are advantages and disadvantages to both types of brakes, and for economic reasons, most heavy trucks, which use the front disc and rear drum arrangement.