# Bicycle Brake System

How a bicycle brake turns your squeeze on the lever into pads pinching the wheel, from cable and rim brakes to disc brakes with oil hydraulics\.

By chocopoule

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/evfawnzY08wO)

## Transcript

### 1. How does a bike stop?

A spinning wheel carries a lot of motion energy\. To stop, the bike has to get rid of it\. Brakes do this by rubbing on part of the wheel\. Let's follow one squeeze from your fingers to the wheel\.

Drag anywhere to turn the bike and look around\.

### 2. The brake lever

It all starts with your fingers on the lever\. The lever swings on a small hinge called a pivot\. Your fingers pull far from the pivot, so a gentle squeeze becomes a stronger pull close to it\.

A lever trades distance for force: your fingers move a long way, the cable only a little\.

### 3. A cable carries the pull

A thin steel cable runs inside a tough tube called the housing\. The lever pulls the cable, and it slides along inside the housing down to the brake\. The housing stays put, so the pull arrives right where it is needed\.

The steel cable is only about 1\.5 mm thick\.

### 4. Pads pinch the rim

The cable closes the caliper: two curved arms that swing on one bolt, like a pair of tongs\. Rubber brake pads on their tips squeeze both sides of the metal rim, and the rubbing slows the wheel\.

Movements are enlarged here so you can see them\. Real pads travel only a few millimetres\.

### 5. Motion turns into heat

Rubbing is called friction, and friction makes things warm, like rubbing your hands on a cold day\. The wheel's motion energy becomes heat in the rim and pads\. On a long downhill, easing off now and then helps the brakes cool\.

The warm metal is tinted orange here so you can see the heat\.

### 6. Disc brakes

Many bikes brake on a disc instead of the rim\. A thin steel disc called a rotor is bolted to the wheel's hub and spins with it\. A caliper fixed to the fork squeezes pads onto the rotor, so a wet or muddy rim matters less\.

A common rotor is 160 mm across and less than 2 mm thick\.

### 7. Pushing with oil

Many disc brakes use oil in a hose instead of a cable\. Squeezing the lever pushes a small piston, and because a liquid cannot be squashed, the push travels down the hose\. At the caliper, the oil pushes pistons that press the pads onto the rotor\.

Air can be squashed, so a bubble in the hose makes the lever feel spongy\.

### 8. Stopping well

When you brake, your weight shifts forward onto the front wheel, so the front brake does most of the stopping\. Squeeze both brakes smoothly rather than grabbing them\. Let go, and springs and seals pull the pads back so the wheel spins freely again\.

A gentle, steady squeeze stops you sooner than a wheel that skids\.