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Views: 28 Author: Site Editor Publish Time: 2025-12-08 Origin: Site
When it comes to braking system selection, commercial vehicles (such as heavy-duty trucks, buses, and vans) differ significantly from passenger cars: passenger cars mostly use disc brakes, while commercial vehicles, especially heavy-duty models, still primarily rely on drum brakes. This difference isn't due to technological lag, but rather to the commercial vehicle's usage scenarios, load requirements, and operational characteristics. This article will analyze the underlying reasons behind the commercial vehicle preference for drum brakes, focusing on the structural advantages and performance adaptability of drum brakes, combined with the characteristics of core components such as brake pads and drums.
Drum brakes consist of components such as the brake drum, brake pads (shoes), and wheel cylinders. Their enclosed structure and force distribution are highly compatible with the operational needs of commercial vehicles.
The brake drum, the core component of a drum brake, is a closed cylindrical structure, typically made of high-strength ductile iron (tensile strength ≥400 MPa). With a wall thickness of 15-20 mm, it can withstand the enormous radial forces and thermal shocks generated during braking. In contrast, the disc brake rotor is an open-faced disc. Under the same heavy load, it is prone to cracking at the edges due to stress concentration.
When a commercial vehicle is fully loaded, a single wheel can carry several tons of load. During braking, the radial pressure exerted by the brake pads (shoes) on the brake drum exceeds 10 MPa. The closed structure of the drum structure evenly distributes this force throughout the drum, while the disc brake pads only apply axial force on the sides of the disc, which can easily cause disc deformation under prolonged heavy loads.
Drum brakes amplify braking force through a "self-amplification effect." During braking, the brake pads (shoes) expand outward under the thrust of the wheel cylinder. Contact with the rotating brake drum generates friction, which in turn pushes the pads even tighter against the drum wall, creating a "force superposition." This characteristic enables drum brakes to generate greater braking force than disc brakes at lower brake oil pressures (8-10 MPa).
Commercial vehicles, due to their heavy weight and payload, require a stronger base braking force. For example, a 10-ton truck can provide a braking torque exceeding 3000 N·m, while a disc brake of the same size typically does not exceed 2000 N·m. Achieving the same braking force requires larger diameter brake discs and multi-piston calipers, significantly increasing costs.
Commercial vehicle operating scenarios (such as long-distance haulage, heavy-load climbing, and frequent starts and stops) place special demands on braking system durability, maintenance costs, and reliability, and drum brakes precisely meet these requirements.
When a commercial vehicle continuously descends a mountainous road, the braking system is subjected to prolonged, high-intensity operation, and brake drum temperatures can soar to 600-800°C. While the closed structure of drum brakes is less efficient in heat dissipation than disc brakes, the contact area between the brake pads (shoes) and the brake drum is larger (typically 30%-50% larger than a disc brake of the same size), resulting in more even heat distribution and less prone to "thermal fade" caused by localized overheating. Furthermore, commercial vehicle brake drums often utilize a bimetallic design: an inner layer of high-thermal-conductivity cast iron (thermal conductivity ≥ 50 W/(m·K)) and an outer layer of heat-resistant alloy, ensuring structural stability at high temperatures. Brake pads are made of sintered metal, containing over 50% copper and iron fibers. The friction coefficient decay rate at high temperatures is less than 15%, ensuring stable braking performance on long downhill slopes.
Commercial vehicles often operate on muddy, dusty, and unpaved roads. The enclosed structure of drum brakes effectively prevents mud, sand, and gravel from entering the braking core, reducing component wear. Disc brakes, on the other hand, have exposed discs and pads, making them susceptible to foreign matter becoming lodged, leading to abnormal brake noise or uneven wear.
The frequency of brake part replacement for commercial vehicles directly impacts operating costs, and drum brakes offer significant advantages in this regard:
Longer brake pad (shoe) life: Commercial vehicle drum brake pads can be up to 15-20mm thick and feature a higher friction material density, resulting in a design lifespan of 100,000-150,000 kilometers, two to three times that of disc brake pads (30,000-60,000 kilometers).
Repairable and Reusable Brake Drums: Brake drums can be lathe-finished after wear, up to three to four times, for a total service life exceeding 300,000 kilometers. Brake discs, on the other hand, require replacement if wear exceeds 0.5mm and are irreparable.
Simplified Maintenance: Replacing drum brake pads requires opening the brake drum without removing the wheel hub, and can be completed in 30 minutes at a typical repair station. Disc brakes require disassembly of the caliper, wheel hub, and other components, taking two to three times longer than drum brakes.
The braking system of commercial vehicles is an integrated system. The synergy between drum brakes, clutch plates, brake lines, and other components further solidifies their application.
The clutch plates of commercial vehicles(especially manual transmission models) must withstand enormous torque (heavy-duty truck engines typically exceed 1500 Nm). The smoothness of their engagement and disengagement directly impacts braking effectiveness. The linear braking force output characteristics of drum brakes complement the friction transmission of clutch plates.
When starting a heavily loaded vehicle, slowly depressing the brake pedal gradually increases the braking force of the drum brakes. This, combined with the gradual engagement of the clutch plates, prevents vehicle jerking. Disc brakes, on the other hand, offer a more responsive braking force. However, when combined with high-torque clutch plates, this can lead to starting shock and increased component wear.
Commercial vehicles commonly use pneumatic braking systems (operating pressure 0.6-0.8 MPa), and the wheel cylinder structure of drum brakes is more suitable for pneumatic actuation: pneumatic cylinders offer high thrust and moderate response speed, which, combined with the drum brake's "self-energizing effect," enables efficient braking. Adapting disc brakes to pneumatic systems requires larger pistons, which not only increases costs but also may cause excessive wear on the brake pads due to excessive thrust.
Commercial vehicles favor drum brakes due to a combination of structural strength, usage scenarios, and maintenance costs. Their closed structure accommodates heavy loads, their self-energizing effect meets high braking force requirements, their pollution resistance adapts to complex road conditions, and their long lifespan meets operational economics—these advantages are precisely the most critical requirements for commercial vehicles. Although disc brakes offer superior heat dissipation and responsiveness, drum brakes remain the most cost-effective option for heavy-load, high-frequency, and low-cost commercial vehicle operations.
With technological advancements, commercial vehicles are also experimenting with hybrid "front disc, rear drum" solutions (front discs for sensitive braking, rear drums for heavy load handling). However, drum brakes' dominance in the commercial vehicle sector remains difficult to replace in the short term. For commercial vehicles, choosing a braking system is never a matter of technological advancement, but rather the optimal solution based on practicality and adaptability.If you are looking for suitable high-performance brake drum or related brake parts,welcome visit our website:https://www.evfriction.com.Our EV company is a reliable brake parts supplier.You can contact us by jessicabrakes12@gmail.com or +86-13363216781 if you have any questions.
