Bike brakes work by using friction to slow down or stop the wheels from turning. There are two main types of bike brakes: rim brakes and disc brakes. Each uses a different mechanism to achieve this, but the fundamental principle remains the same: converting kinetic energy into heat energy through friction.
Rim Brakes
Rim brakes, as the name suggests, apply friction to the rim of the wheel. Here's a breakdown of how they operate:
- Lever Action: When you squeeze the brake lever on your handlebars, you pull a cable.
- Cable Tension: This cable runs to the brake calipers, which are mounted on the frame or fork near the wheel rim.
- Calipers Engage: The cable tension causes the brake calipers to close.
- Pads Contact Rim: As the calipers close, brake pads (made of a friction material like rubber or a composite) press against the wheel rim.
- Friction Slows Wheel: The friction between the pads and the rim slows the wheel's rotation, ultimately bringing the bike to a stop.
- Release: When you release the brake lever, the cable slackens, and a spring in the calipers pulls the brake pads away from the rim, allowing the wheel to rotate freely again.
Disc Brakes
Disc brakes use a rotor (a metal disc) attached to the wheel hub. When you apply the brakes, pads clamp onto the rotor, creating friction to slow down the wheel. Disc brakes can be either mechanical (cable-operated) or hydraulic.
Mechanical Disc Brakes
Mechanical disc brakes operate similarly to rim brakes, using a cable to actuate the braking force:
- Lever Action: Squeezing the brake lever pulls a cable.
- Caliper Activation: The cable pulls a lever on the brake caliper.
- Pad Engagement: This lever pushes one or both brake pads against the rotor.
- Friction Slows Wheel: The friction between the pads and the rotor slows the wheel.
- Release: Releasing the lever allows a spring to retract the pads.
Hydraulic Disc Brakes
Hydraulic disc brakes use hydraulic fluid to transmit force from the lever to the caliper:
- Lever Action: When you squeeze the brake lever, a piston in the master cylinder pushes hydraulic fluid through the brake hose.
- Fluid Pressure: The pressurized fluid travels to the caliper at the wheel.
- Piston Activation: The fluid pressure forces pistons in the caliper to extend.
- Pad Engagement: These pistons push the brake pads against the rotor.
- Friction Slows Wheel: The friction slows the rotor and, consequently, the wheel.
- Release: When the brake is released, a spring retracts the pistons and pads away from the rotor, and fluid flows back to the master cylinder.
In summary, both rim brakes and disc brakes rely on friction to slow or stop a bike. Rim brakes use pads against the wheel rim, while disc brakes use pads against a rotor. Hydraulic disc brakes offer enhanced power and modulation compared to mechanical systems due to the efficiency of hydraulic fluid in transmitting force.
