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Views: 26 Author: Site Editor Publish Time: 2025-12-04 Origin: Site
In a vehicle's braking system, the brake drum, brake pads, and brake discs are the core components for deceleration and braking. Although they all belong to the same braking system, they exhibit significant differences in their structural design, operating principles, and application scenarios. At the same time, they work together to ensure vehicle braking efficiency. This article will delve into the differences and connections between these three brake components to help readers fully understand the operational logic of the braking system.
The appearance and structural design of the brake drum, brake pads, and brake discs directly determine their operation and application scenarios.
The brake drum is a cylindrical metal component fixed to the wheel, typically made of gray cast iron or ductile iron, with a smooth inner friction surface. Its structural characteristic is its closed nature: the entire braking process occurs within the drum, with the brake pads (shoes) concealed within the drum. During operation, they expand from the inside outward to contact the drum wall. Commercial vehicle brake drums are larger, typically 300-500mm in diameter and 15-20mm thick. Cooling fins are often cast on the outer surface to mitigate the high temperatures generated by heavy braking.
Brake discs are flat, circular discs that rotate with the wheel, secured to the wheel hub. They are primarily made of gray cast iron or high-carbon alloy cast iron. Unlike the enclosed brake drum, their structure is open: the disc is exposed, and the brake pads (caliper-type) clamp against it from both sides, generating friction. Passenger car brake discs typically have diameters of 250-400mm and thicknesses of 20-35mm. Ventilated discs and grooved discs are common, with holes or patterns used to enhance heat dissipation.
Brake pads are the components that directly generate friction, but their shape must be adapted to the brake drum or disc:
Drum brake pads (shoes): These are curved, matching the curvature of the brake drum's inner wall. Supported by a metal shoe on the back, they are pushed outward by the wheel cylinder, creating friction against the drum's wall.
Disc brake pads: These are block-shaped structures fixed within the brake caliper. During operation, a piston pushes against the brake disc, creating a flat friction surface.
The core difference between the two is the direction of friction: drum brake pads generate radial friction (perpendicular to the drum's radius), while disc brakes pads generate axial friction (parallel to the disc's axis).
All three share the same core principle of converting kinetic energy through friction, but their force transmission and amplification mechanisms differ fundamentally.
During braking, hydraulic or pneumatic pressure pushes the wheel cylinder piston, causing the curved brake pads to expand outward, creating close contact with the rotating brake drum's inner wall. Two forces are generated at this time:
Friction: This directly converts kinetic energy into heat, achieving deceleration.
Self-amplification: The reaction force generated by the friction between the brake pad and the drum further pushes the pads open, creating a "force superposition" that amplifies braking force without the need for additional hydraulic pressure. This characteristic enables drum brake systems to generate strong braking force at low pressures, making them suitable for heavy-duty applications.
During braking, the pistons in the brake caliper push the brake pads against the rotating brake discfrom both sides, generating braking force through flat friction. This force transmission is a "linear drive": the braking force is directly related to the piston thrust. Multi-piston calipers or increased piston area are required to increase braking force. Disc systems do not have a self-amplification effect, but they offer more uniform frictional contact and a braking response speed approximately 30% faster than drum systems.
Comparison Dimensions | Drum Brake System (Brake Drum + Shoe) | Disc Brake System (Brake Disc + Pad) |
Brake Force Amplification | Relies on the self-energizing effect, resulting in high output at low pressure. | Relies on piston thrust, requiring high actuation pressure. |
Heat Dissipation | Closed structure, slow heat dissipation | Open structure, fast heat dissipation. |
Response Speed | Slow (0.3-0.5 seconds) | Fast (0.1-0.2 seconds) |
Maintenance | Requires drum disassembly, more complex. | Directly exposed, easy to replace. |
Irrespective of the braking system, improper maintenance will shorten component lifespan:
Brake Pad Replacement Threshold: Drum brake pads must be replaced when their thickness is less than 3mm, and disc brake pads less than 2mm. Failure to do so will cause wear on the brake drum/disc.
Brake Disc/Drum Inspection: Brake discs with grooves exceeding 0.5mm or deformation require replacement; brake drum inner wall wear exceeding 2mm requires repair or replacement.
Avoiding "Sticks": Before parking the vehicle for extended periods, gently apply the brakes to remove surface moisture and prevent rust and sticking between the brake pads and the disc/drum.
Although the brake drum, brake pads, and brake discs differ in form and principle, they all serve the core goal of "safe braking": the brake pads are the friction medium, and the brake drum/disc is the friction carrier. The matching of these three directly determines braking performance.Understanding the differences and relationships between the three can not only help car owners maintain the braking system scientifically, but also make them understand a truth: the quality of a braking system does not lie in the technical level of "drum" and "disc", but in whether it is perfectly adapted to the requirements of the vehicle model - this is the classic embodiment of "practicality is king" in automotive engineering.To learn more information about brake parts,you can visit our website:https://www.evfriction.com .And you can contact us by jessicabrakes12@gmail.com if you have any questions.
