Brakes

The Science of Stopping: It's All About Friction - Bicycle Brakes Convert Kinetic Energy (Motion) Into Thermal Energy (Heat).

The approximate braking distance can be found by determining the work required to dissipate the bike’s kinetic energy:

$work = (μ \times mass \times gravity) \times distance kinetic Energy = \frac{1}{2} \times mass \times {velocity}^{2}$

Through the Work-Energy Principle it can then be said that:

$(μ \times mass \times gravity) \times distance = \frac{1}{2} \times mass \times {velocity}^{2}$

Finally, by rearranging the equation and cancelling like terms we can form an equation for braking distance:

$distance = \frac{{velocity}^{2}}{(2 \times μ \times gravity)}$

μ = coefficient of friction

How's it Work? Metallic or ceramic pads are pressed against a metal rotor that's attached to the wheel.
Advantages: powerful, protected from contaminates, better heat dissipation
Disadvantages: expensive, heavy, difficult to maintain