Heat is pretty much always the enemy. On everything from computers to cars, it's necessary to keep things cool. On a bicycle, the brakes are the source of most heat due to friction. Either rim or disc brakes, both get nice and toasty when under heavy use. The methods for dealing with the heat are pretty cool though. For example, here is a heat sink for an electrical component:
Blue anodization extra
The fins cool the device by dissipating heat into the surrounding air. This passive cooling method that works well for an air cooled motorcycle engine as well. The engine below is covered with fins to handle all the heat from the engine running:
On an mountain bike, heat is dissipated on the rotors of disc brakes by adding slots in the rotor. These pull air in and cool the rotor:
Standard 6 bolt rotor
Now for the exciting news of the blog: Shimano has a new set of XT brakes with some sweet finned brake pads:
These fins are on the pads, not the brake, but can apparently reduce the pad temperature by around 50 degrees. That's a great way to prolong pad and rotor life, as well as improve braking!