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

Braking Distance

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

work = (μ × mass × gravity) × distance

kinetic Energy = 1/2 × mass × velocity 2

Through the Work-Energy Principle it can then be said that:
(μ × mass × gravity) × distance = 1/2 × mass × velocity 2

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

d i s t a n c e = v e l o c i t y 2 ( 2 × μ × g r a v i t y )

μ = coefficient of friction

Rim Brake

  • How's it Work?  Rubber pads are pressed against the rim of the wheel.
  • Advantages: inexpensive, lightweight, easy to maintain, mechanically simple
  • Disadvantages: easily contaminated, less braking power

Disc Brake

  • 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

Diagram of bike showing where the rim brake and disc brake are.