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 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.Heitmann, J. A. The Automobile and American Life. McFarland, 2009, , pp. 11ff
Etymology 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 🚲.
History
Uses
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.
Technical aspects
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.
Types
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".
Dynamics
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.
Performance
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 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.
Parts
One bicycle may have up to a thousand parts.
Frame
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.
Historically, women's bicycle frames had a top tube that connected in the middle of the seat tube instead of the top, resulting in a lower standover height at the expense of compromised structural integrity, since this places a strong bending load in the seat tube, and bicycle frame members are typically weak in bending. This design, referred to as a step-through frame or as an open frame, allows the rider to mount and dismount in a dignified way while wearing a skirt or dress. While some women's bicycles continue to use this frame style, there is also a variation, the mixte, which splits the top tube laterally into two thinner top tubes that bypass the seat tube on each side and connect to the rear fork ends.
Another style is the recumbent bicycle. These are inherently more aerodynamic than upright versions, as the rider may lean back onto a support and operate pedals that are on about the same level as the seat. The world's fastest bicycle is a recumbent bicycle but this type was banned from competition in 1934 by the Union Cycliste Internationale.
Historically, materials used in bicycles have followed a similar pattern as in aircraft, the goal being high strength and low weight. Since the late 1930s, alloy steels have been used for frame and fork tubes in higher quality machines. By the 1980s, aluminum welding techniques had improved to the point that aluminum tube could safely be used instead of steel. Since then aluminum alloy frames and other components have become popular due to their light weight, and most mid-range bikes are now aluminum alloy. More expensive bikes sometimes use titanium or more often carbon fibre laid-up in resin due to its significantly lighter weight and profiling ability, allowing designers to make a bike both stiff and compliant by arranging the angles of the laid-up fibres optimally. Virtually all professional racing bicycles now use carbon fibre frames, as they have the best strength to weight ratio. A typical modern carbon fiber frame can weigh less than .
Wood and bamboo, a natural composite material with high strength-to-weight ratio and stiffness, have been used for bicycles since 1894. Modern versions use bamboo for the primary frame with glued metal connections and parts.
Drivetrain and gearing
The drivetrain begins with pedals which rotate the cranks, which are held in axis by the bottom bracket. Most bicycles use a chain to transmit power to the rear wheel. A very small number of bicycles use a shaft drive to transmit power. Hydraulic bicycle transmissions have been built, but they can be inefficient and complex.
Since cyclists' legs are most efficient over a narrow range of pedaling speeds, or cadence, a variable gear ratio helps a cyclist to maintain an optimum pedalling speed while covering varied terrain. Some, mainly utility, bicycles use hub gears with between 3 and 14 ratios, but most use the generally more efficient derailleur system, by which the chain is moved between different cogs called chainrings and sprockets to select a ratio. A derailleur system normally has two derailleurs, or mechs, one at the front to select the chainring and another at the back to select the sprocket. Most bikes have two or three chainrings, and from 5 to 12 sprockets on the back, with the number of theoretical gears calculated by multiplying front by back. In reality, many gears overlap or require the chain to run diagonally, so the number of usable gears is fewer.
An alternative to chain drive is to use a toothed belt. These work much the same as a chain, they are popular with commuters as they require little maintenance. They are slightly less efficient than chains and cannot be shifted across a cassette of sprockets, and are used either as single speed or with a hub gear.
Different gears and ranges of gears are appropriate for different people and styles of cycling. Multi-speed bicycles allow gear selection to suit the circumstances: a cyclist could use a high gear when cycling downhill, a medium gear when cycling on a flat road, and a low gear when cycling uphill. In a lower gear, every turn of the pedals leads to fewer rotations of the rear wheel. This allows the energy required to move the same distance to be distributed over more pedal turns, reducing fatigue when riding uphill, with a heavy load, or against strong winds. A higher gear allows a cyclist to make fewer pedal turns to maintain a given speed, but with more effort per turn of the pedals.
With a chain drive transmission, a chainring attached to a crank drives the chain, which in turn rotates the rear wheel via the rear sprocket(s) (cassette or freewheel). There are four gearing options: two-speed hub gear integrated with chain ring, up to 3 chain rings, up to 12 sprockets and hub gear built into rear wheel (3-speed to 14-speed). The most common options are either a rear hub or multiple chain rings combined with multiple sprockets (other combinations of options are possible but less common).
Steering
The handlebars connect to the stem that connects to the fork housing the front wheel. The whole assembly rotates about the steering axis, held by the headset bearings.