History
Several innovators contributed to the history of the bicycle by developing precursor human-powered vehicles. The documented ancestors of today's modern bicycle were known as push bikes, Draisines or hobby horses. To use the Draisine, first introduced to the public in Paris by the German Baron Karl von Drais in 1818[3], the operator sat astride a wooden frame supported by two in-line wheels and pushed the vehicle along with his/her feet while steering the front wheel.
In the early 1860s, Frenchmen Pierre Michaux and Pierre Lallement took bicycle design in a new direction by adding a mechanical crank drive with pedals on an enlarged front wheel. Several why-not-the-rear-wheel inventions followed, the best known being the rod-driven velocipede by Scotsman Thomas McCall in 1869. The French creation, wrought of iron and wood, developed into the "penny-farthing" (more formally an ordinary bicycle), featuring a tubular steel frame on which were mounted wire spoked wheels with solid rubber tires. These bicycles were not, however, for the faint hearted, due to the very high seat and poor weight distribution.
The subsequent dwarf ordinary addressed some of these faults by reducing the front wheel diameter and setting the seat further back, necessitating the addition of gearing, effected in a variety of ways, to attain sufficient speed. However, 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 connecting the pedals held with the frame to the back wheel. 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 a secondbicycle craze, 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. 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, cycling 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.
[edit]Uses for bicycles
Bicycles have been and are employed for many uses:
- Utility: bicycle commuting and utility cycling
- Work: mail delivery, paramedics, police, and general delivery.
- Recreation: bicycle touring, mountain biking, BMX and physical fitness.
- Racing: track racing, criterium, roller racing and time trial to multi-stage events like the Tour of California, Giro d'Italia, the Tour de France, the Vuelta a España, the Volta a Portugal, among others.
- Military: scouting, troop movement, supply of provisions, and patrol. See bicycle infantry.
- Show: entertainment and performance, e.g. circus clowns
Cycling has many health benefits and does not directly contribute to global warming or environmental pollution.
[edit]Technical aspects
Since the first bicycle, many important details have been improved, especially with the advent of modern materials and computer-aided design. These have allowed for a proliferation of specialized bicycle types.
[edit]Types of bicycle
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 more common types include utility bicycles,mountain bicycles, racing bicycles, touring bicycles, cruiser bicycles, and BMX bicycles. Less common are tandems, lowriders, tall bikes, fixed gear, folding models and recumbents (one of which was used to set the IHPVA Hour record).
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".
[edit]Dynamics
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, endo or front wheelie.
[edit]Performance
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.[4] 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%.[5][6] 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 human being traveling on a bicycle at low to medium speeds of around 10-15 mph (15-25 km/h), using only the energy required to walk, is the most energy-efficient means of transport generally available. Air drag, which is proportional to the square of speed, requires dramatically higher power outputs as speeds increase. A bicycle which 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 orhuman powered vehicle. On an upright bicycle, the rider's body creates about 75% of the total drag of the bicycle/rider combination.
In addition, the carbon dioxide generated in the production and transportation of the food required by the bicyclist, per mile traveled, is less than 1/10th that generated by energy efficient cars.[7]
[edit]Construction and parts
In its early years, bicycle construction drew on pre-existing technologies; more recently, bicycle technology has, in turn, contributed ideas in both old and new areas.
[edit]Frame
The great majority of today's bicycles have a frame with upright seating which looks much like the first chain-driven bike[2]. Such upright bicycles almost always 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, referred to as a step-through 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 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. Because of its persistent image as a "women's" bicycle, step-through frames are not common for larger builds.
A more recent development 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[1].
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. Celluloid found application in mudguards, and aluminum alloys are increasingly used in components such as handlebars, seat post, and brake levers. In the 1980s aluminum 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 and even bamboo.
[edit]Drivetrain
- For more details on this topic, see bicycle gearing.
Since cyclists' legs are most efficient over a narrow range of cadences, a variable gear ratio is helpful to maintain an optimum pedalling speed while covering varied terrain.
The drivetrain begins with pedals which rotate the crank arms, which are held in axis by the bottom bracket. On a bicycle with shaft drive, a gear set at the bottom bracket turns the shaft, which then turns the rear wheel via a gear set connected to the wheel's hub. The rear hub may provide several different gear ratios.
On a bicycle with chain drive, a crank arm may have one or more chainrings or sprockets attached. A chainring drives the chain, which in turn rotates the rear wheel via the rear sprockets (cassette or freewheel). A gearing system is used to vary the number of rear wheel revolutions produced by each turn of the pedals.
When the bicycle chain shifts to a larger rear sprocket, or to a smaller front sprocket (a lower gear) every turn of the pedal leads to fewer rotations in the freewheel (and hence the rear wheel). This allows the force required to move the same distance to be distributed over more pedal cycles, reducing fatigue when riding uphill, with a heavy load, or against strong winds. The reverse process allows the cyclist to make fewer pedal cycles to maintain a higher speed, but with more effort per cycle.
Road bicycles have close set multi-step gearing, which allows fine control of cadence, while utility bicycles offer fewer, more widely spaced speeds. Mountain bikes, touring bikes and many entry-levelracing bicycles offer an extremely low gear to facilitate climbing slowly on steep hills. Single-speed bicycles have only one gear.
[edit]Steering and seating
The handlebars turn the fork and the front wheel via the stem, which rotates within 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 handlebarwhich can provide better low-speed handling due to the wider nature of the bars.
Saddles also vary with rider preference, from the cushioned ones favored by short-distance riders to narrower saddles which allow more room for 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. Differing saddle designs exist for male and female cyclists, accommodating the genders' differing anatomies, although bikes typically are sold with saddles most appropriate for males.
A recumbent bicycle has a reclined chair-like seat that some riders find more comfortable than a saddle, especially riders who suffer from certain types of seat, back, neck, shoulder, or wrist pain. Recumbent bicycles may have either under-seat or over-seat steering.
[edit]Brakes
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.Disc brakes are common on 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. 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 levers mounted on the handlebars and transmitted via Bowden cables or hydraulic lines to the friction pads. A rear hub brake may be either hand-operated or pedal-actuated, as in the back pedal coaster brakes which were popular in North America until the 1960s, and are still common in children's bicycles.
Track bicycles do not have brakes. Brakes are not required for riding on a track because all riders ride in the same direction around a track which does not necessitate sharp deceleration. 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. While it is illegal in most jurisdictions to cycle on roads without brakes, a fixed-gear bike without brakes can be slowed by skidding the rear wheel. This involves 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.
[edit]Suspension
Bicycle suspension refers to the system or systems used to suspend the rider and all or part of the bicycle. This serves two purposes:
- To keep the wheels in continuous contact with rough surfaces in order to improve control.
- To isolate the rider and luggage from jarring due to rough surfaces.
Bicycle suspensions are used primarily on mountain bicycles, but are also common on hybrid bicycles, and can even be found on some road bicycles, as they can help deal with problematic vibration. Suspension is especially important on recumbent bicycles, since while an upright bicycle rider can stand on the pedals to achieve some of the benefits of suspension, a recumbent rider cannot.
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