A bicycle (or bike) is a pedal-driven, human-powered vehicle with two wheels, one behind the other, attached to a frame. The basic shape and configuration of a typical bicycle's frame, wheels, pedals, saddle, and handlebars have hardly changed since the first chain-driven model was developed around 1885, although many important improvements have since been made, especially since the advent of modern materials and computer-aided design. These have allowed for a proliferation of specialized designs for individuals who pursue a particular type of cycling.
The bicycle has affected history considerably, in both the cultural and industrial realms. First introduced in nineteenth-century Europe, bicycles now number over one billion worldwide, providing the principal means of transportation in many regions, notably China and the Netherlands. They are also a popular form of recreation and have been adapted for use in many other fields of human activity, including children's toys, adult fitness, military and police applications, courier services, and sports.
Through the centuries, several inventors and innovators contributed to the development of the bicycle. Its earliest known forebears were called velocipedes, and included many types of human-powered vehicles. The first documented ancestor of the modern bicycle, first introduced to the public in Paris by the German Baron Karl von Drais in 1818. Known as a pushbike, Draisienne, or hobby horse, it was powered by the action of the rider's feet pushing against the ground. The Draisienne had two in-line wheels connected by a wooden frame. The rider sat astride and pushed it along with his feet, while steering the front wheel.
Scottish blacksmith Kirkpatrick MacMillan refined this in 1839 by adding a mechanical crank drive to the rear wheel, thus creating the first true "bicycle" in the modern sense. In the 1850s and 1860s, Frenchmen Ernest Michaux and Pierre Lallement took bicycle design in a different direction, placing the pedals on an enlarged front wheel. Their creation, which came to be called the "Boneshaker" or "penny-farthing" (more formally an ordinary bicycle), featured a heavy steel frame on which they mounted wooden wheels with iron tires. The primitive bicycles of this generation were difficult to ride, and the high seat and poor weight distribution made for dangerous falls.
The subsequent dwarf ordinary addressed some of these faults by adding gearing, reducing the front wheel diameter, and setting the seat further back, with no loss of speed. Having to both pedal and steer via the front wheel remained a problem. Starley's nephew, J. K. Starley, J. H. Lawson, and Shergold solved this problem by introducing the chain drive. These models were known as dwarf safeties, or safety bicycles, for their lower seat height and better weight distribution. Starley's 1885 Rover is usually described as the first recognizably modern bicycle. Soon, the seat tube was added, creating the double-triangle, diamond frame of the modern bike.
New innovations increased comfort, and ushered in the 1890s Golden Age of Bicycles. In 1888, Scotsman John Boyd Dunlop introduced the pneumatic tire, which soon became universal. Soon after, the rear freewheel was developed, enabling the rider to coast without the pedals spinning out of control. This refinement led to the 1898 invention of coaster brakes. Derailleur gears and hand-operated, cable-pull brakes were also developed during these years, but were only slowly adopted by casual riders. By the turn of the century, bicycling clubs flourished on both sides of the Atlantic, and touring and racing were soon extremely popular.
Bicycles and horse buggies were the two mainstays of private transportation just prior to the automobile, and the grading of smooth roads in the late 19th century was stimulated by the wide use of these devices.
The 1968 Vienna Convention on Road Traffic considers a bicycle to be a vehicle, and a person controlling a bicycle is considered a driver. The traffic codes of many countries reflect these definitions and demand that a bicycle satisfy certain legal requirements, sometimes even including licensing, before it can be used on public roads. In many jurisdictions it is an offence to use a bicycle that is not in roadworthy condition. In most places, bicycles must have functioning front and rear lights, or lamps, when ridden after dark. As some generator or dynamo-driven lamps only operate while moving, rear reflectors are frequently also mandatory. Since a moving bicycle makes very little noise, in many countries bicycles must have a warning bell for use when approaching pedestrians, equestrians and other bicyclists.
A number of formal and industry standards exist for bicycle components, to help make spare parts exchangeable. Examples are:
Nearly all modern upright bicycles feature the "diamond frame," a truss, consisting of two triangles: the front triangle and the rear triangle. The front triangle consists of the head tube, top tube, down 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 top tube connects the head tube to the seat tube at the top, and the down tube connects the head tube to the bottom bracket. The rear triangle consists of the seat tube and paired chain stays and seat stays. The chain stays run parallel to the chain, connecting the bottom bracket to the rear dropouts. The seat stays connect the top of the seat tube at or near the same point as the top tube) to the rear dropouts.
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 purportedly allows the rider to mount and dismount in a dignified way while wearing a skirt or dress, an action made difficult by a properly-sized diamond frame. While some women's bicycles continue to use this frame style, there is also a hybrid form, the "mixte" or step-through frame, which splits the top tube into two small top tubes that bypass the seat tube and connect to the rear dropouts. The ease of stepping through is also appreciated by those with limited flexibility or other joint problems. Unfortunately for the old tall man, because of its persistent image as a "women's" bicycle, the vast majority of mixte frames are quite small.
Historically, materials used in bicycles have followed a similar pattern as in aircraft, the goal being strength and low weight. Since the late 1930s alloy steels have been used for frame and fork tubes in higher quality machines. Celluloid found application in mudguards, and aluminium alloys are increasingly used in components such as handlebars, seat post, and brake levers. In the 1980s aluminium alloy frames became popular, and their affordability now makes them common. More expensive carbon fiber and titanium frames are now also available, as well as advanced steel alloys.
The drivetrain begins with pedals which rotate the cranks, which connect to the bottom bracket. Attached to the (usually right) crank arm may be one or more chainrings or sprockets which drive the chain, which in turn rotates the rear wheel via the rear sprockets (cassette or freewheel). Various gearing systems may be interspersed between the pedals and rear wheel; these gearing systems vary the number of rear wheel revolutions produced by each turn of the pedals.
Since cyclists' legs produce a limited amount of power most efficiently over a narrow range of cadences, a variable gear ratio is helpful to maintain an optimum pedalling speed while covering varied terrain.
The fundamental working/application of a rear gear is explained as follows. When the bicycle chain is linked to a freewheel with higher radius (the lower gear) every cycle on the pedal leads to fewer rotations in the freewheel (and hence the rear wheel). This results in covering lesser distance for each pedal cycle. The primary source of tiredness in bicycling is the power that the rider dissipates and not the energy (for instance, a person covering a mile at 1 mile per hour will get less tired than a person covering a mile at 10 miles an hour, even though both spend the same energy). Thus power lost indicates the effort spent. In an upslope, the energy needed to cover a distance is greater than that needed on a flat surface for the same distance. Thus to maintain the same effort (or power lost) even while riding on an upslope, a rider should shift to a lower gear with the pedalling speed maintained at the same level as that on a flat surface. This adjustment increases the time taken to cover the considered distance. Thus more time is spent in dissipating the higher energy needed in an upslope. This helps to maintain a power (or effort) same as that of a flat surface. The dual of this strategy where the rider shifts to a higher gear can be used to increase the speed of travel at the cost of increased power dissipation. Gears, hence, give the rider a provision to choose a desired speed at the cost of effort and vice versa.
Road bicycles have "close set" multi-step gearing, which allows very fine control of cadence, while utility cycles offer fewer, more widely spaced speeds. "Mountain bikes" and most entry-level road racing bikes may offer an extremely low gear to facilitate climbing slowly on steep hills.
The handlebars turn the fork and the front wheel via the "stem", which articulates with the headset. Three styles of handlebar are common. "Upright handlebars," the norm in Europe and elsewhere until the 1970s, curve gently back toward the rider, offering a natural grip and comfortable upright position. "Drop handlebars" are "dropped," offering the cyclist either an aerodynamic "crouched" position or a more upright posture in which the hands grip the brake lever mounts. Mountain bikes feature a "straight handlebar," which helps prevent the rider from pitching over the front in case of sudden deceleration.
Variations on these styles exist. "Bullhorn" style handlebars are often seen on modern time trial bicycles, equipped with two forward-facing extensions, allowing a rider to rest the entire forearm on the bar. These are usually used in conjunction with the "aero bar," a pair of forward-facing extensions spaced close together, to promote better aerodynamics. The Bullhorn was banned from ordinary road racing because it is difficult for the rider to control in bike traffic.
"Saddles" also vary with rider preference, from the cushioned ones favoured by short-distance riders to narrower saddles which allow more free leg swings. Comfort depends on riding position. With comfort bikes and hybrids the cyclist sits high over the seat, their weight directed down onto the saddle, such that a wider and more cushioned saddle is preferable. For racing bikes where the rider is bent over, weight is more evenly distributed between the handlebars and saddle, and the hips are flexed, and a narrower and harder saddle is more efficient.
A recumbent bicycle has a reclined chair-like seat that is more comfortable than a saddle, especially for riders who suffer from certain types of back pain.
Modern bicycle brakes are either "rim brakes," in which friction pads are compressed against the wheel rims, "internal hub brakes," in which the friction pads are contained within the wheel hubs, or "disc brakes." A rear hub brake may be either hand-operated or pedal-actuated, as in the back pedal coaster brakes which were the rule in North America until the 1960s, and are still common in children's bicycles. Hub drum brakes do not cope well with extended braking, so rim or disc brakes are favored in hilly terrain. With hand-operated brakes, force is applied to brake handles mounted on the handle bars and then transmitted via Bowden cables or hydraulic lines to the friction pads. Disc brakes appeared in the late 1990s on some off-road bicycles, tandems and recumbent bicycles, but are considered impractical on road bicycles, which rarely encounter conditions where the advantages of discs are significant.
For track cycling, track bicycles do not have brakes. Brakes are not required for riding on a track because all riders ride in the same direction and there are no corners or other traffic. Track riders are still able to slow down because all track bicycles are fixed-gear, meaning that there is no freewheel. Without a freewheel, coasting is impossible, so when the rear wheel is moving, the crank is moving. To slow down one may apply resistance to the pedals. Cyclists who ride a track bike without brake(s) on the road can also slow down by skidding, by unweighting the rear wheel and applying a backwards force to the pedals, causing the rear wheel to lock up and slide along the road. Most track bike frames and forks do not have holes for mounting brakes, although with their increasing popularity among some road cyclists, some manufacturers have designed their track frames to enable the fitting of brakes.
Bicycle suspension refers to the system or systems used to suspend the rider and all or part of the bicycle in order to protect them from the roughness of the terrain over which they travel. Bicycle suspension are used primarily on mountain bicycles, but are also common on hybrid bicycles, and can even be found on some road bicycles.
Some components, which are often optional accessories on sports bicycles, are standard features on utility bicycles to enhance their usefulness and comfort. Chainguards and mudguards, or fenders, protect clothes and moving parts from oil and spray. Kick stands help with parking. Front-mounted wicker or steel baskets for carrying goods are often used. Rear racks or carriers can be used to carry items such as school satchels. Parents sometimes add rear-mounted child seats and/or an auxiliary saddle fitted to the crossbar to transport children.
"Toe-clips and toestraps," or clipless pedals, help to keep the foot planted firmly on the pedals, and enable the cyclist to pull as well as push the pedals. Technical accessories include solid-state speedometers and odometers for measuring distance. Other accessories include lights, reflectors, tire pump, security lock, mirror, and horn. A bicycle helmet is classified by some as an accessory, but as an item of clothing by others.
Many cyclists carry tool kits containing at least a tire patch kit (and/or a spare tube), tire levers, and hex wrenches. A single tool once sufficed for most repairs. More specialised parts now require more complex tools, including proprietary tools specific for a given manufacturer. Some bicycle parts, particularly hub-based gearing systems, are complex, and many prefer to leave maintenance and repairs to professional bicycle mechanics. Others maintain their own bicycles, enhancing their enjoyment of the hobby of cycling.
In both biological and mechanical terms, the bicycle is extraordinarily efficient. In terms of the amount of energy a person must expend to travel a given distance, investigators have calculated it to be the most efficient self-powered means of transportation. From a mechanical viewpoint, up to 99 percent 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 percent.  In terms of the ratio of cargo weight a bicycle can carry to total weight, it is also a most efficient means of cargo transportation.
A person traveling on a bicycle at low to medium speeds of around 10-15 mph (16-24 km/h), using only the energy required to walk, is the most energy-efficient means of transport generally available. Air drag, which increases with the square of speed, requires dramatically higher power outputs with increasing speed. A bicycle that places the rider in a seated position, supine position or, more rarely, prone position, and which may be covered in an aerodynamic fairing to achieve very low air drag, is referred to as a recumbent bicycle or human powered vehicle. Humans create the greatest amount of drag on an upright bicycle at about 75 percent of the total drag.
A bicycle stays upright by being steered so as to keep its center of gravity over its wheels. This steering is usually provided by the rider, but under certain conditions may be provided by the bicycle itself.
A bicycle must lean in order to 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 in order to flip longitudinally. This action, especially if performed on purpose, is known as a stoppie or front wheelie.
Bicycle manufacturing proved to be a training ground for other industries and led to the development of advanced metalworking techniques, both for the frames themselves and for special components such as ball bearings, washers, and sprockets. These techniques later enabled skilled metalworkers and mechanics to develop the components used in early automobiles and aircrafts. J. K. Starley's company became the Rover Cycle Company Ltd. in the late 1890s, and then the Rover auto maker. The Morris Motor Company (in Oxford) and Škoda also began in the bicycle business, as did the Wright Brothers.
In general, U.S. and European cycle manufacturers used to assemble cycles from their own frames and components made by other companies, although very large companies (such as Raleigh) used to make almost every part of a bicycle (including bottom brackets, axles, etc.) In recent years, those bicycle makers have greatly changed their methods of production. Now, almost none of them produce their own frames. Many newer or smaller companies only design and market their products; the actual production is done by eastern companies. For example, some sixty percent of the world's bicycles are now being made in China. Despite this shift in production, as nations such as China and India become more wealthy, their own use of bicycles has declined due to the increasing affordability of cars and motorcycles. One of the major reasons for the proliferation of Chinese-made bicycles in foreign markets is the lower cost of labor in China.
The diamond-frame safety bicycle gave women unprecedented mobility, contributing to their emancipation in Western nations. As bicycles became safer and cheaper, more women had access to the personal freedom they provided, and so the bicycle came to symbolize the New Woman of the late nineteenth century, especially in Britain and the United States.
The bicycle was recognized by nineteenth-century feminists and suffragists as a "freedom machine" for women. American Susan B. Anthony said in a New York World interview on February 2, 1896: "Let me tell you what I think of bicycling. I think it has done more to emancipate women than anything else in the world. It gives women a feeling of freedom and self-reliance. I stand and rejoice every time I see a woman ride by on a wheel… the picture of free, untrammelled womanhood." In 1895 Frances Willard, the tightly-laced president of the Women’s Christian Temperance Union, wrote a book called How I Learned to Ride the Bicycle, in which she praised the bicycle she learned to ride late in life, and which she named "Gladys," for its "gladdening effect" on her health and political optimism. Willard used a cycling metaphor to urge other suffragists to action, proclaiming, "I would not waste my life in friction when it could be turned into momentum."
The male anger at the freedom symbolized by the New (bicycling) Woman was demonstrated when the male undergraduates of Cambridge University chose to show their opposition to the admission of women as full members of the university by hanging a woman in effigy in the main town square—tellingly, a woman on a bicycle. This was as late as 1897. In the 1890s, the bicycle craze led to a movement for so-called rational dress, which helped liberate women from corsets and ankle-length skirts and other restrictive garments, substituting the then-shocking bloomers.
Sociologists suggest that bicycles enlarged the gene pool for rural workers, by enabling them to easily reach the next town and increase their "courting radius." In cities, bicycles helped reduce crowding in inner-city tenements by allowing workers to commute from more spacious dwellings in the suburbs. They also reduced dependence on horses, with all the knock-on effects this brought to society. Bicycles allowed people to travel for leisure into the country, since bicycles were three times as energy efficient as walking, and three to four times as fast.
Bicycles have been and are employed for many uses.
Bicycles can be categorized in different ways: e.g., by function, by number of riders, by general construction, by gearing or by means of propulsion. The common types include utility bicycles, mountain bicycles, racing bicycles, touring bicycles, cruiser bicycles, and BMX bicycles. Less common types include tandems, recumbents, and folding models. Unicycles, tricycles, and quadracycles are not strictly bicycles, as they have respectively one, three and four wheels, but are often referred to informally as "bikes" by users.
All links retrieved February 2, 2013.
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