A bicycle, also called a pedal cycle, bike, push-bike or cycle, is a human-powered or motor-assisted, pedal-driven, single-track vehicle, with two wheels attached to a frame, one behind the other. A bicycle rider is called a cyclist or bicyclist.
The bicycle was invented in Europe in the 19th century. By the early 21st century, there were more than 1 billion bicycles. Bicycles are the principal means of transport in many regions. They are also popular for recreation, and have been adapted for use as children's toys. Bicycles are used for commuting, shopping, fitness, military and police applications, courier services, bicycle racing, and artistic cycling.
The basic shape and configuration of a typical upright or "safety" bicycle, has changed little since the first chain-driven model was developed around 1885. However, many details have been improved, especially since the advent of modern materials and computer-aided design. These have allowed for a proliferation of specialized designs for many types of cycling. In the 21st century, electric bicycles have become popular.
The bicycle's invention has had an enormous effect on society, both in terms of culture and of advancing modern industrial methods. Several components that played a key role in the development of the car were initially invented for use in the bicycle, including ball bearings, pneumatic tires, chain-driven sprockets, and tension-spoked wheels.
The first known appearance in English print of the word bicycle was in The Daily News in 1868, to describe "Bysicles and trysicles" on the "Champs Elysées and Bois de Boulogne". The word was first used in 1828 in French to describe a two-wheeled chaise, a horse-drawn carriage. The design of the bicycle was an advance on the velocipede, although the words were used with some degree of overlap for a time.
Other words for bicycle include "bike", "pushbike", "pedal cycle", or "cycle". In Unicode, the code point for "bicycle" is U+1F6B2. The entity 🚲 in HTML produces 🚲.
Bicycles are used for transportation, bicycle commuting, and utility cycling. The energy taken to cycle to a particular distance takes less than the energy to walk as far by four-fifths or 80 percent. They are also used professionally by mail carriers, paramedics, police, messengers, and for deliveries. Military uses of bicycles included communications, reconnaissance, troop movement, supply of provisions, and patrol, such as in bicycle infantries.
They are also used for fun, including bicycle touring, mountain biking, physical fitness, and play. Bicycle sports include racing, BMX racing, track racing, criterium, roller racing, sportives and time trials. They are also used for entertainment and pleasure in other ways, such as in organised mass rides, artistic cycling and freestyle BMX.
The bicycle has been continually adapted and improved. Modern materials and computer-aided design have made bicycles safer and more comfortable, and helped to create many more types of bicycle.
Bicycles can be categorized in many different ways: by function, by number of riders, by general construction, by gearing or by means of propulsion. The more common types include utility bicycles, mountain bicycles, racing bicycles, touring bicycles, hybrid bicycles, cruiser bicycles, BMX bikes and electric bicycles. Less common are tandems, low riders, tall bikes, fixed gear, folding models, amphibious bicycles, cargo bikes and recumbents .
Unicycles, tricycles and quadracycles are not strictly bicycles, as they have respectively one, three and four wheels, but they are cycles and the qualifier "bi" is not used in some other languages, such as "velo" or "fiets".
A bicycle stays upright while moving forward by being steered so as to keep its center of mass over the wheels, that is in line with the resultant force of gravity and centrifugal force. This steering is usually provided by the rider, but under certain conditions, may be provided by the bicycle itself.
The combined center of mass of a bicycle and its rider must lean into a turn. This lean is induced by a method known as countersteering, which can be performed by the rider turning the handlebars directly with the hands or indirectly by leaning the bicycle.
Short-wheelbase or tall bicycles, when braking, can generate enough stopping force at the front wheel to flip longitudinally. The act of purposefully using this force to lift the rear wheel and balance on the front without tipping over is a trick known as a stoppie, endo, or front wheelie.
The bicycle is extraordinarily efficient in both biological and mechanical terms. The bicycle is the most efficient human-powered means of transportation in terms of energy a person must expend to travel a given distance, when travelling slowly or equipped with an aerodynamic fairing. From a mechanical viewpoint, up to 99% of the energy delivered by the rider into the pedals is transmitted to the wheels, although the use of gearing mechanisms may reduce this by 10–15% and there is also a small amount of tire slip.
A human traveling on a bicycle at low to medium speeds of about 16–24 km/h (10–15 mph) uses only the power required to walk. Air drag, which is proportional to the square of speed, requires dramatically higher power outputs as speeds increase. If the rider is sitting upright, the rider's body creates about 75% of the total drag of the bicycle/rider combination. Drag can be reduced by seating the rider in a more aerodynamically streamlined position. Drag can also be reduced by covering the bicycle with an aerodynamic fairing. The fastest recorded unpaced speed on a flat surface with a standing start was the hour record in 2016: over 92 km/h (57 mph) with a highly streamlined bicycle.
One bicycle may have up to a thousand parts.
Most modern bicycles have a frame with upright seating that looks much like the first chain-driven bike. These upright bicycles frequently have a diamond frame, a truss consisting of two triangles: the front triangle and the rear triangle. The front triangle consists of the top tube and down tube (connected by the head tube), and seat tube. The head tube contains the headset, the set of bearings that allows the fork to turn smoothly for steering and balance. The rear triangle consists of the seat tube, with the bottom bracket at the bottom, and paired chain stays and seat stays, connecting at the rear dropouts, where the axle for the rear wheel is held. The frame's shape allows the rider's weight to be distributed in a way that does not misshapen or compress the entire frame as it turns.