# Bicycle

A bicycle riding in place on rollers: its frame, wheels, chain, gears, steering and brakes, and how they turn leg power into travel

By bright\-dolphin\-694f7a1a

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/W987iNPuaW2c)

## Transcript

### 1. Meet the bicycle

A bicycle turns the push of your legs into smooth, quiet travel\. This one is riding in place on rollers: drums that spin under the wheels\. Drag anywhere to turn it and look from every side\.

Pinch or scroll to move closer\.

### 2. Two triangles make a frame

The frame is two triangles of tubes that share the seat tube\. A triangle cannot be squashed out of shape without bending a side, so slim tubes can carry a grown\-up rider\. Frames are usually steel, aluminium or carbon fibre\.

A carbon racing frame can weigh less than one kilogram\.

### 3. Wheels hang from their spokes

Each wheel has about 32 thin spokes, pulled tight like guitar strings\. The hub in the middle hangs from the spokes above it, so thin wire can hold a heavy rider\. Air in the tyre soaks up the bumps\.

John Boyd Dunlop made air\-filled bicycle tyres practical in 1888\.

### 4. Pedals, chain and sprockets

Your feet turn the cranks, and the cranks turn the big front chainring\. Its teeth pull the chain, and the chain turns a small toothed wheel, a sprocket, on the back wheel\. Only the back wheel is driven; the front one just rolls along\.

A clean, oiled chain passes almost all of your pedal effort on to the wheel\.

### 5. Gears: easy or fast

The back wheel carries sprockets of different sizes, and the gear changer moves the chain between them\. On the biggest, one turn of the pedals spins the wheel about one and a half times: easy for hills\. On the smallest, it spins almost four times: harder work, but fast\.

This chainring has 42 teeth and the sprockets have 11 to 28\.

### 6. Steering keeps you up

You balance mostly by steering\. When the bike starts to lean, you turn the front wheel a little toward the lean, and the wheels roll back underneath you\. Because the steering line is slanted, the tyre touches the ground a little behind it, so the front wheel tends to straighten itself\.

Spinning wheels help a little, but they are not the main reason a bike stays up\.

### 7. Brakes squeeze the rim

Pull a brake lever and a cable tugs two rubber pads against the metal rim of the wheel\. The rubbing turns the wheel's motion into a little warmth, and the bike slows down\. Gentle pressure on both brakes gives the smoothest stop\.

### 8. An idea that keeps rolling

The first two\-wheeler, built in 1817, had no pedals: riders pushed along with their feet\. By 1885 the chain\-driven safety bicycle looked much like this one\. A bicycle can have up to a thousand parts, all working together every time you ride\.

Riding at an easy pace takes about as much power as walking, yet is three or four times faster\.