Skip to content
Know.itKnow.it
Create an animated lesson
On request

This article is free to read. Creating a lesson uses your daily or stored credits; review the language and settings before starting.

How do bicycle gears work?

TechnologyLesson on requestFree to read

Quick answer

Bicycle gears work by changing the ratio of pedal turns to rear-wheel turns. The chain links a front chainring to a rear sprocket. A large front with a small rear gives high speed but hard pedaling; a small front with a large rear gives low speed but easy climbing. A derailleur moves the chain between sprockets to shift gears.

Bicycle gears change the ratio between how fast you pedal and how fast the rear wheel turns. By shifting the chain between differently sized front and rear sprockets, you trade pedal effort for speed or climbing ease.

Step by step

  1. You push the pedals, which turn the front chainring.
  2. The chain, engaged with the chainring teeth, moves and pulls the rear sprocket.
  3. The rear sprocket turns the rear wheel hub, which rotates the wheel.
  4. The gear ratio—front teeth divided by rear teeth—determines how many wheel turns occur per pedal turn.
  5. To shift, you move the shifter, which pulls a cable that moves the derailleur.
  6. The derailleur pushes the chain sideways onto a different sprocket, changing the ratio.

Key things to understand

  1. The chain connects the front chainrings, turned by the pedals, to the rear cassette sprockets, which drive the rear wheel.
  2. When the chain is on a large front chainring and a small rear sprocket, each pedal turn rotates the wheel many times, giving high speed but requiring more effort.
  3. When the chain is on a small front chainring and a large rear sprocket, each pedal turn rotates the wheel fewer times, giving low speed but easier climbing.
  4. The gear ratio is the number of teeth on the front chainring divided by the number of teeth on the rear sprocket.
  5. A derailleur moves the chain sideways between sprockets while you pedal lightly, changing the gear ratio to match the terrain.

Labelled diagram

  1. Pedals

    Rider pushes pedals, turning the front chainring.

  2. Front chainring

    Toothed wheel attached to the pedals; size sets the gear ratio.

  3. Chain

    Links front chainring to rear sprocket, transferring force.

  4. Rear sprocket

    Toothed wheel on the rear wheel; size sets the gear ratio.

  5. Derailleur

    Moves chain sideways to change sprockets while pedaling.

Bicycle gear system

Real-world examples

  • On a flat road, a cyclist selects a large front chainring and a small rear sprocket to travel far with each pedal stroke.
  • When climbing a steep hill, the cyclist shifts to a small front chainring and a large rear sprocket to pedal with less force.
  • A racing bike often has two front chainrings and eleven rear sprockets, giving 22 gear combinations for varied terrain.
  • A mountain bike may have a single front chainring and a wide-range rear cassette, simplifying shifting on rough trails.

Common mistake

✗ Myth: More gears always make you faster.

✓ Fact: More gears give more options to match your pedaling effort to the terrain, but top speed depends on the highest gear ratio and your pedaling power. A bike with fewer gears can be just as fast if its highest ratio is the same.

People also ask

What does a derailleur do on a bike?
A derailleur is a mechanism that moves the chain sideways between sprockets of different sizes. When you shift, a cable pulls the derailleur, which pushes the chain onto a new sprocket. This changes the gear ratio. The rear derailleur also keeps the chain tensioned as it moves.
Why do bikes have gears?
Bikes have gears to let you adjust how hard you pedal and how fast you go. On flat ground, a high gear lets you travel far with each pedal stroke. On hills, a low gear reduces the force needed, so you can climb without exhausting your legs. Gears match your effort to the terrain.
How do you shift gears on a bike?
You shift by using the shifters on the handlebars. While pedaling lightly, move the shifter to pull or release the cable. This moves the derailleur, which guides the chain onto a different sprocket. Always pedal forward during a shift, and avoid shifting under heavy load to prevent damage.
What is a gear ratio?
A gear ratio is the number of teeth on the front chainring divided by the number of teeth on the rear sprocket. It tells you how many times the rear wheel turns for each full turn of the pedals. A higher ratio means more speed per pedal stroke but more effort.
Why do I need to pedal while shifting?
The derailleur can only move the chain sideways if the chain is moving. Pedaling lightly lets the chain climb onto the next sprocket smoothly. Shifting while pedaling hard can bend the chain or damage the teeth.
How many gears does a typical bike have?
A typical bike has between 7 and 30 gears, calculated by multiplying the number of front chainrings by the number of rear sprockets. For example, 3 front and 10 rear gives 30 possible combinations. Not all combinations are used because some cause the chain to rub.
Why does a lower gear make climbing easier?
A lower gear means the rear wheel turns fewer times per pedal turn. This reduces the distance the bike moves per stroke, so you push less weight against gravity. Your legs spin faster but with less force, which is easier on steep hills.

Part of the guide: Everyday Machines →