Derailleur

A bike part moves the chain.

It moves the chain from one gear to another. This lets you change how you ride.

A rider pulls a lever. This pulls a wire. The wire moves a guide. The guide pushes the chain to a new gear.

Some bikes use a battery. A small motor moves the part. This can save time for racers.

This part is called a derailleur. It helps you go up big hills. It makes riding fun!

A derailleur is a tool on a bicycle. It moves the chain from one gear to another. This helps a rider change how they pedal.

Most bikes have a front and a rear derailleur. The front one moves the chain between large rings. The rear one moves the chain between smaller cogs.

A rider uses a lever to shift gears. This lever pulls a Bowden cable. A Bowden cable is a wire inside a tube. The wire moves a guide from side to side. This guide pushes the chain onto a new gear.

The rear derailleur has a special job. It also takes up slack in the chain. When a chain moves to a smaller gear, it gets loose. The derailleur has a cage with two small wheels. We call these pulleys. One is the jockey pulley. The other is the tension pulley. The cage uses these pulleys to keep the chain tight.

Some modern bikes use electronic shifting. A battery sends power to a small motor. The motor moves the derailleur for the rider. This can save time during a race.

A derailleur is a clever tool on a bicycle. It is a device that moves the chain from one sprocket to another. This helps riders change gears as they pedal.

The name comes from a French word meaning "derailer." This originally described a device used to knock a train off its tracks. Today, it helps cyclists handle different paths.

Without it, riding up steep hills would be much harder.

How does this thing work? Most systems use a moveable chain-guide. A rider pulls a lever on the handlebars. This action moves a Bowden cable, which is a wire inside a tube. The cable changes the tension to move the guide from side to side. This movement "derails" the chain onto a new sprocket.

The rear derailleur has an extra job too. It uses a spring-loaded cage to take up slack. When the chain moves to a smaller gear, it gets loose. The cage uses two small wheels, called pulleys, to keep the chain tight.

People have been building these for a long time. Early designs in the late 1800s used rods to move the chain. In 1905, a man named Paul de Vivie invented a two-speed rear version. He used it while riding through the Alps. In 1937, derailleurs were used in the Tour de France. This meant riders did not have to take their wheels off to change gears.

In 1964, a company called Suntour made a new design called the slant-parallelogram. This design is still used on many bikes today.

Many famous companies make these parts now. Shimano is from Japan, SRAM is from the USA, and Campagnolo is from Italy.

In 1985, Shimano introduced indexed shifting. This made shifting more precise. Instead of sliding a lever, the shifter clicks into a specific spot. Modern racing bikes are very advanced. Some have 10 gears in the back, and others have 11.

Some new mountain bike parts even have 13 gears.

Modern technology is changing things even more. Some high-end bikes now use electronic shifting. Instead of a cable, a battery sends power to a small motor. This motor moves the derailleur for the rider. This can help a racer save time. You might see these parts on a mountain bike or a road bike. Whether it is a simple cable or a tiny motor, it all helps you ride better.

A derailleur is a specialized mechanical device used to move a bicycle chain between different sprockets. This mechanism allows a cyclist to change gears, making it easier to climb hills or go faster on flat ground.

The term comes from the French word "dérailleur," which means "derailer." This name originally described a tool used to knock a train off its tracks. On a bicycle, however, the device is essential for managing the drivetrain.

Modern derailleurs typically function through a moveable chain-guide. This guide is operated remotely using a Bowden cable. The cable connects to a shifter located on the handlebars or the down tube. When a rider operates the shifter, the tension in the cable changes. This change in tension moves the chain-guide from side to side. This movement "derails" the chain, forcing it onto a different sprocket.

The rear derailleur performs two distinct roles. First, it moves the chain between the rear sprockets. Second, it acts as a tensioner to manage chain slack. When a rider shifts to a smaller sprocket, the chain becomes loose. The rear derailleur uses a spring-loaded cage to take up this extra length. This cage contains two small wheels called pulleys. The top pulley is the jockey pulley, and the bottom is the tension pulley.

Cycling history shows a long evolution of these mechanisms. In the late 19th century, early versions like the Protean two-speed were built. In 1905, Paul de Vivie invented a two-speed rear derailleur for his trips through the Alps. Early systems often used metal rods to move the chain. By 1937, the Tour de France introduced derailleurs to the race. This was a major change because riders no longer had to dismount to change wheels.

Technological breakthroughs have shaped modern riding. In 1964, Suntour invented the slant-parallelogram rear derailleur. This design allows the jockey pulley to maintain a constant distance from the sprockets. Most modern rear derailleurs still use this pattern. In 1985, Shimano introduced indexed shifting. Unlike friction shifting, which requires manual adjustment to center the chain, indexed shifting uses a ratchet mechanism. This mechanism stops the lever at specific distances for precise gear changes.

Today, the industry is dominated by three main manufacturers: Shimano from Japan, SRAM from the USA, and Campagnolo from Italy.

These companies use different standards for their shift ratios. Shimano systems often use a 2:1 ratio, where a unit of cable movement causes twice as much derailleur travel. SRAM often uses a 1:1 ratio, meaning cable movement and derailleur movement are nearly equal.

Some high-end mountain bikes even use electronic shifting. In these systems, a battery and a small electric motor move the derailleur instead of a manual cable.

Gear capacity and cage length are important technical factors. The cage length is the distance between the two pulleys. This length determines how much chain slack the derailleur can manage. A longer cage is often needed for mountain bikes with many gears. A shorter cage is common for road bikes to reduce weight and improve shifting precision. Some mountain bike derailleurs also include a clutch. This clutch keeps the chain tight to prevent "chain slap," which is when the chain hits the bike frame.