Disk Brakes vs. Drum Brakes: What’s the Difference
Disk and drum brakes are the two main types of brakes used in automobiles. Both play a crucial role in slowing down and stopping vehicles. Drum brakes have been around longer and use cams and shoes to create friction and stop the wheel from turning. Disk brakes came later and work by using calipers to squeeze brake pads against a rotor to slow the wheel. While both braking systems have their pros and cons, disk brakes have become the more dominant technology on modern vehicles.
How Disk Brakes Work
Disk brakes work through a system of rotors, calipers, and brake pads. The rotors are metal discs attached to the wheel hub that rotate along with the wheel. Calipers are assemblies that contain hydraulic pistons positioned on each side of the rotor. The brake pads are positioned inside the calipers, straddling the rotor on both sides.
When the brakes are applied, hydraulic pressure from the brake fluid pushes the caliper pistons inward. This clamps the brake pads against the rotor on both sides, creating friction that slows the rotation of the rotor and wheel, stopping the vehicle.
The clamping force of the caliper against the pads and rotor converts the kinetic energy of the moving wheel into heat energy through friction. This heat is dissipated by the rotor and brake pads which are designed to withstand high temperatures. The pads are made of materials that provide the right amount of friction to stop effectively without damaging the rotor.
How Drum Brakes Work
Drum brakes are a more traditional brake design that has been around for decades. The main components of a drum brake are the brake drums, shoes, and wheel cylinders.
The brake drums are cylindrical metal drums located on each wheel hub that rotate with the wheel. The inner surface of the drum has a machined surface for the brake shoes to contact.
The brake shoes are semicircular pieces lined with friction material that press against the inner surface of the drum. When the brakes are applied, the shoes expand outward and make contact with the drum to create friction and stop the vehicle.
Wheel cylinders contain hydraulic pistons that push the brake shoes outward when the brakes are applied. There are usually two wheel cylinders per brake drum, one for each shoe. The hydraulic pressure from the master cylinder actuates the wheel cylinders to engage the brake shoes against the drum.
When the brakes are applied, hydraulic pressure pushes the wheel cylinder pistons outward, which in turn pushes the brake shoes against the drum. Friction between the brake shoes and drum slows the rotation of the drum and wheel until the vehicle stops.
Disk Brake Advantages
Disk brakes have several key advantages over drum brakes that make them the preferred choice for most vehicles and applications today.
One major advantage is better stopping power. Disc brakes provide more consistent braking force as pressure is applied to the brake pedal. This allows the vehicle to stop in a shorter distance. The clamping force of the brake pads against the rotor creates significant friction to slow the wheels down rapidly.
Disk brakes are also highly resistant to fade. Fade occurs when the brake components overheat during heavy or repeated braking. This causes a loss of braking power. Disk brakes are designed with high heat thresholds and the exposed rotors allow air cooling. This keeps them performing optimally even under extreme braking conditions where drum brakes would fade.
The open design of disc brakes also makes them self-cleaning. Dust, water and other contaminants are thrown off the rotors by centrifugal force as the wheels spin. This maintains good contact between the pads and rotors. Drum brakes are fully enclosed so contaminants build up inside, reducing effectiveness over time.
Drum Brake Advantages
Drum brakes have some key advantages over disk brakes:
Simpler design – Drum brakes have a very simple design with few moving parts. The brake shoes press against the inside of the drum to create friction and slow the vehicle.
Protected internals – With drum brakes, all the brake components are contained within the sealed drum, protecting them from dirt, water and other road contaminants.
Low cost – The simple design and sealed nature of drum brakes makes them less expensive to manufacture and maintain than disk brakes. This makes them ideal for basic vehicle applications where cost is a priority.
Maintenance
One of the maintenance differences between disk and drum brakes is how the brake pads/shoes are replaced. With disk brakes, the caliper and brake pads can be easily accessed and replaced. Drum brake shoes are inside the sealed drum, requiring the wheel, drum and hardware to be removed for access. This makes pad replacements quicker and simpler with disk brakes.
Disk brakes also tend to require less frequent cleaning than drum brakes. The open design of disk brakes allows better air circulation which helps dissipate heat and prevents brake dust buildup. Drum brakes can trap dust inside the drum, requiring more frequent cleaning.
Adjusting disk brakes involves adjusting the caliper mechanism or replacing worn parts. Drum brakes require manual adjustment of the brake shoes and hardware using adjusting tools. Disk brakes are generally self-adjusting, requiring less frequent adjustment than drum brakes.
Cost Comparison
When it comes to cost, drum brakes have traditionally been the more affordable option compared to disk brakes. Here’s a look at some of the key differences:
Disk brakes come at a premium price. The disk brake assembly including the rotor, caliper, brake pads, and other hardware is generally more expensive than a basic drum brake setup. The larger, high performance brake rotors required for disk brakes also cost more than standard brake drums.
Drum brakes offer savings. The simple design of drum brakes makes them cheaper to manufacture and install. The brake drums themselves are less expensive to produce than rotors, especially for larger vehicles that would require big brake discs. This makes drum configurations appealing for keeping costs down.
However, the long term costs should also be considered. Because disk brakes tend to be more durable and require less frequent maintenance, they may save money over time. The cost advantage for drums also diminishes as performance requirements go up. Race cars and high-end sports cars rely on advanced multi-piston calipers and rotors to deliver top braking force, outweighing the higher parts cost.
Applications
Disk brakes are now standard on the majority of passenger cars. Their superior stopping power and resistance to fading make them ideal for regular driving. Drum brakes were the dominant choice for most of automotive history, but have been gradually phased out on most passenger vehicles. However, drum brakes are still commonly found on the rear wheels of some passenger cars as an affordable supplement to the disk brakes on the front wheels.
For pickups and large trucks, the preference has historically been drum brakes due to their lower cost. But disk brakes have been making inroads as performance expectations increase even for work vehicles. Disk brakes provide better stopping ability when towing or hauling heavy loads. Now drum brakes are primarily just used on the rear axle of heavy-duty trucks.
Performance cars almost universally rely on disk brakes for their superior heat tolerance and resistance to fading. High-end sports cars integrate even larger rotors and multi-piston calipers to handle repeated hard braking when driving at the limit. Performance oriented upgrades are also available in the aftermarket for many regular passenger cars, allowing bigger and better disk brakes to be adapted to improve stopping power.
The Future
Looking ahead, most experts predict disk brakes will continue to gain traction and become more widespread. As technology improves and costs come down, the advantages of disk brakes make them an appealing option for more and more vehicle types and applications.
One trend to watch is the development of hybrid brake systems that incorporate elements of both disk and drum brakes. For example, using a disk brake system in the front wheels and drum brakes in the rear. This allows manufacturers and engineers to optimize the benefits of each brake type based on factors like vehicle weight distribution and desired performance characteristics.
Manufacturers are also exploring ways to incorporate regenerative braking systems along with friction brakes. Regenerative braking captures kinetic energy during braking and converts it to electricity to improve fuel efficiency. Combining this with optimized friction braking can maximize both stopping power and energy regeneration.
In the long run, improved materials and designs will likely make disk brakes even more effective and affordable. So while drums brakes still have some advantages today, expect to see disk brakes become the dominant choice for more and more vehicles in the future.
Conclusion
In summary, both disk and drum brake systems have their advantages and disadvantages. Disk brakes tend to provide stronger stopping power and better performance, especially in wet conditions. They dissipate heat faster and are less prone to fading. However, drum brakes are simpler in design, easier to service, and often cheaper to manufacture. They also provide smoother braking action in the rear.
For most passenger vehicles, disk brakes are the optimal choice for the front wheels where heat dissipation and stopping power are more critical. Drum brakes are still commonly used in the rear, especially in basic economy models, as they provide adequate braking and keep costs down. Performance vehicles and trucks tend to utilize disk brakes on all four wheels for maximum stopping ability.
Looking ahead, drum brakes are likely to be phased out in favor of disks, especially with the rise of electric vehicles. With regenerative braking taking over some of the workload, disks provide the better combination of performance, safety, and longevity. However, drum brakes will continue to have applications in certain niche roles given their simplicity and low cost.
Overall, when choosing between disk and drum brake systems, drivers should consider their usage needs. For most everyday use, a mix of disks in the front and drums in the rear is sufficient. But for towing, hauling, or performance needs, four-wheel disk brakes are recommended.