Millions of people use bicycles to get around, exercise, race, and enjoy recreational riding. The basic design of a bicycle has changed little since the first chain-driven model was developed around 1885, but modern materials and computer-aided design have enabled a wide range of specialized designs for many uses. The bicycle is the most efficient human-powered machine for transportation, converting up to 99% of the energy a rider puts into it into forward motion.

The name bicycle derives from the French word for two wheels, referring to the design of a machine that is a combination of a chair and a wheeled vehicle. Its etymology also suggests that the bicycle is designed to facilitate human-powered movement, and is thus a bicyclus, or wheeled animal. The term bicycle is a convenient shorthand for any machine that converts human power into movement. The modern bicycle is often referred to simply as a bike, although it is more accurately described as a cycle.

A bicycle consists of a seat, two wheels, and pedals that connect to a crankshaft through a chain. A rider sits on the seat and steers by leaning over the handlebars, which are connected to the frame via a stem and fork. The rider pushes down on the pedals with his or her feet, turning them to move the crankshaft, which in turn drives the rear wheel through a chain. The chain is looped around a cog on the crankshaft and then attached to the rear wheel’s sprockets. The rider’s feet are used to drive the bicycle, and he or she may shift gears to vary the speed of the crankshaft and, consequently, the speed of the wheel.

Bicycles are the most popular vehicles in the world. In developed countries they are used mostly for transportation, with some also serving as a means of recreation and exercise. The bicycle is a popular means of commuting in cities, where it reduces congestion and pollution and provides a cost-effective alternative to car travel. The bicycle is also used in military and police applications, courier services, and by cyclists engaging in racing or artistic cycling.

The bicycle is the most efficient human-powered mode of transportation, converting up to 99% of a rider’s effort into forward motion. It is able to transport cargo more efficiently than any other land vehicle, including trucks and buses. It has revolutionized transportation in industrialized countries, allowing commuters to escape from inner-city crowding and to reach suburban office buildings or shops. In some developing nations, the bicycle has transformed rural life by allowing farmers to carry large loads over long distances. The bicycle has also revolutionized leisure time for millions of people by making it possible to travel longer distances for sport and recreation at speeds that are three to four times faster than walking, with relatively little exertion. The bicycle has become a symbol of freedom and independence, and is often associated with youth culture and counterculture.