Disc brakes have a number of advantages over drum brakes.
They also have some disadvantages. In most cases, the advantages outweigh the disadvantages. One of the biggest advantages is that disc brakes can generate and transfer greater amounts of heat to the atmosphere; because most of the friction area of a rotor is exposed to air, cooling is far more rapid than for a drum brake. This faster cooling makes them better suited for high-performance driving or heavy-duty vehicles and reduces the likelihood of brake fade.
Also, because of their shape, rotors tend to scrape off water more effectively. After being driven through water, disc brakes operate at peak performance almost immediately. Further, due to their design, disc brakes are self-adjusting and do not need periodic maintenance or rely on a self-adjusting mechanism that is prone to sticking (see the Disc Brake Calipers section). Lastly, in most cases, disc brakes are also easier to service than drum brakes.
While disc brakes have a number of benefits over drum brakes, there are some disadvantages.
Probably the most apparent disadvantage is that disc brakes are much more prone to noise. Their design tends to create squeals and squeaks, which can be very annoying. Many a technician has spent time servicing perfectly functional disc brakes due to excessive noise complaints.
Another issue is that the rotors warp easier than in drum brake systems. Since the brake pads are pressing on each side of the rotor, thickness variations of as small as 0.0003″ (0.0076 mm) can cause brake pedal pulsations, requiring resurfacing or replacement. The last disadvantage is that since disc brakes are not self-energizing, they need higher clamping forces, which requires a power booster. This also makes it harder to use them as effective parking brakes.
While there may appear to be more disadvantages to disc brakes versus drum brakes, the advantages are generally considered much more critical than the disadvantages. Thus, disc brakes are preferred over drum brakes in most applications.