1, the biggest advantage of drum brakes is that when the same braking torque is obtained, the diameter of brake drum is much smaller than that of disc brake.  Large trucks, large buses and other large vehicles require great braking torque, and the space in the hub is very limited, so their brake systems generally use drum brakes.
2, relative to the drum brake disc has the advantages of simple structure, low manufacturing cost, easy installation and a hand brake mechanism. So drum brakes are applied to the rear wheels of low front wheel drive small cars.
3, the disc brake and drum brake, disc brake is the biggest advantages of good heat dissipation. Because the brake disc is a "clip" action on the brake disc, the brake disc will not affect the contact area after heating expansion.
4, the brake drum brake disc relative mechanism are exposed, but also more conducive to heat dissipation.