Rim Brakes: Rim brakes are inexpensive, light, mechanically simple, easy to maintain, and powerful. However, they perform relatively poorly when the rims are wet. This problem is less serious with rims made of aluminium than on those with carbon fibre, steel or chromed rims. Because the rims can carry debris from the ground to the brake pads, rim brakes are more prone to clogging with mud or snow than disc brakes (where both braking surfaces are high off the ground), particularly when riding on unpaved surfaces. The light weight of rim brakes also makes them desirable in road racing bicycles.
Are disc brakes better than Rim brakes?
A disc brake consists of a metal disc attached to the wheel hub that rotates with the wheel. Calipers are attached to the frame or fork along with pads that squeeze together on the disc. As the pads drag against the disc, the wheel - and thus the bicycle - is slowed as kinetic energy (motion) is transformed into thermal energy (heat). (In basic operation, disc brakes are identical to rim brakes.) A bicycle disc brake may be mechanically actuated, as with a Bowden cable, or hydraulically actuated, or a combination of the two.