A bicycle chain transfers force from the rider’s pedals to the rear wheel. When the rider pushes the pedals, the crank turns the front chainring, which pulls the chain around the rear sprocket and turns the wheel.
On a conventional derailleur bicycle, the chain is part of a drivetrain that also includes the crankset, cassette, derailleurs and freehub. Changing gears moves the chain between sprockets of different sizes, allowing the rider to trade speed for easier climbing or the reverse.
The chain is not the same as the belt or shaft used on some alternative bicycles. Chains remain common because they are efficient, relatively light and compatible with many gear systems. Regular cleaning, lubrication and replacement help prevent wear, skipping and damage to the chainrings and sprockets.