ratio of word probabilities predicted from brain for door and bicycle

door	bicycle
top 10 words in brain distribution (in article): material design build wood iron size type record cut time	top 10 words in brain distribution (in article): fiber city build town century state Unite produce production country
top 10 words in brain distribution (not in article): card blade steel service store company product information process provide	top 10 words in brain distribution (not in article): sheep wool house cotton fabric store street weave hamlet pig
times more probable under door 30 20 10 6 4 2.5 1.25 1 1.25 2.5 4 6 10 20 30 times more probable under bicycle (words not in the model)
A door'" is a moveable barrier used to cover an opening. Doors are used widely and are found in walls or partitions of a building or space, furniture such as cupboards, cages, vehicles, and containers. A door can be opened to give access and closed more or less securely using a combination of latches and locks. (See article Door security). Doors are nearly universal in buildings of all kinds, allowing passage between the inside and outside, and between internal rooms. When open, they admit ventilation and light. The door is used to control the physical atmosphere within a space by enclosing it, excluding air drafts, so that interiors may be more effectively heated or cooled. Doors are significant in preventing the spread of fire. They act as a barrier to noise. (See article Door safety). They are also used to screen areas of a building for aesthetic purposes, keeping formal and utility areas separate. Doors also have an aesthetic role in creating an impression of what lies beyond. Doors are often symbolically endowed with ritual purposes, and the guarding or receiving of the keys to a door, or being granted access to a door can have special significance. Similarly, doors and doorways frequently appear in metaphorical or allegorical situations, literature and the arts, often as a portent of change. Design and construction styles. Many kinds of doors have specific names, depending on their purpose. The most common variety of door consists of a single rigid panel that fills the doorway. Many variations on this basic design are possible, such as "double" doors that have two adjacent independent panels hinged on each side of the doorway. A "'Dutch door'" or "'stable door'" is divided in half horizontally. Traditionally the top half can be opened to allow a horse or other animal to be fed, while the bottom half remained closed to keep the animal inside. "'Saloon doors'" are a pair of lightweight swing doors often found in public bars. Saloon doors, also known as "'cafe doors'", often use "'double action hinges'", which will return the door to the center, regardless of which direction it is opened, due to the double action springs in the doors. Saloon doors that only extend from knee-level to chest-level are known as "'batwing doors'". A "'blind door'" is a door with no visible trim or operable components. It is designed to blend with the adjacent wall in all finishes, and visually to be a part of the wall, a disguised door. A "'barn door'" is a door characteristic of a barn. They are often always found on barns, and because of a barn's immense size (often) doors are subsequently big for utility. A "'French door'", also called a "'French window'", is a door that has multiple windows ("lights") set into it for the full length of the door. Traditional French doors are assembled from individual small pieces of glass and mullions. These doors are also known as true divided lite[sic] French doors. French doors made of double-pane glass (on exterior doors for insulation reasons) may have a decorative grille embedded between the panes, or may also be true divided lite French doors. The decorative grille may also be superimposed on top of single pane of glass in the door. A "'louvred door'" has fixed or movable wooden fins (often called slats or louvers) which permit open ventilation whilst preserving privacy and preventing the passage of light to the interior. Being relatively weak structures, they are most commonly used for wardrobes and drying rooms, where security is of less importance than good ventilation, although a very similar structure is commonly used to form window shutters. A "'flush door'" is a completely smooth door, having plywood or MDF fixed over a light timber frame, the hollow parts of which are often filled with a cardboard core material. Flush doors are most commonly employed in the interior of a dwelling, although slightly more substantial versions are occasionally used as exterior doors, especially within hotels and other buildings containing many independent dwellings. A "'moulded door'" has the same structure as that of flush door. The only difference is that the surface material is a moulded skin made of HDF MDF. It is commonly used as interior doors. A "'ledge and brace door'" is a door made from multiple vertical planks fixed together by two horizontal planks (the ledges) and kept square by a diagonal plank (the brace). A "'wicket door'" is a normal sized door built into a much larger one, such as the gate of a city or castle. A "'bifold door'" id="bifold"/> is a door unit that has several sections, folding in pairs. Wood is the most common material, and doors may also be metal or glass. Bifolds are most commonly made for closets, but may also be used as units between rooms. A "'sliding glass door'", sometimes called an Arcadia door, is a door made of glass that slides open and sometimes has a screen. "'Australian doors'" are a pair of plywood swinging doors often found in Australian public houses. These doors are generally red or brown in color and bear a resemblance to the more formal doors found in other British Colonies' public houses. A "'false door'" is a wall decoration that looks like a door. In ancient Egyptian architecture, this was a common element in a tomb, the false door representing a gate to the afterlife. They can also be found in the funerary architecture of the desert tribes (e.g., Libyan Ghirza). Hinged doors. Most doors are hinged along one side to allow the door to pivot away from the doorway in one direction but not in the other. The axis of rotation is usually vertical. In some cases, such as hinged garage doors often horizontal, above the door opening. Doors can be hinged so that the axis of rotation is not in the plane of the door to reduce the space required on the side to which the door opens. This requires a mechanism so that the axis of rotation is on the side other than that in which the door opens. This is sometimes the case in trains, such as for the door to the toilet, which opens inward. "'A swing door'" has special hinges that allow it to open either outwards or inwards, and is usually sprung to keep it closed. A "'Mead door'" is a double action pivot door capable of swinging both ways. First introduced by Scott Mead, established in Leicester, England. The Mead door is susceptible to forced entry. Sliding doors. It is often useful to have doors which slide along tracks, often for space or aesthetic considerations. A bypass door"' is a door unit that has two or more sections. The doors can slide in either direction along one axis on parallel overhead tracks, sliding past each other. They are most commonly used in closets, in order to access one side of the closet at a time. The doors in a bypass unit will overlap slightly when viewed from the front, in order not to have a visible gap between them. Doors which slide between two wall panels are called pocket doors'". Sliding glass doors are common in many houses, particularly as an entrance to the backyard. Such doors are also popular for use for the entrances to commercial structures. A "'tambour door'" is made of narrow horizontal slats and "rolls" up and down by sliding along vertical tracks and is typically found in entertainment centres and cabinets. Folding doors. Folding doors have an even number of sections, generally 2 to 4, folding in pairs. The doors can open from either side for one pair, or fold off both sides for two pairs. Rotating doors. A "'revolving door'" normally has four wings leaves that hang on a center shaft and rotate one way about a vertical axis. The door may be motorized, or pushed manually using pushbars. People can walk out of and into the building at the same time. Between the point of access and the point of exit the user walks through an airlock. Revolving doors therefore create a good seal from the outside and help to reduce C and heating costs climate control from the building. This type of door is also often seen as a mark of prestige and glamour for a building and it not unusual for neighbouring buildings to install their own revolving doors when a rival building gets one. A"' butterfly door'" called because of its two "wings". It consists of a double-wide panel with its rotation axle in the centre, effectively creating two separate openings when the door is opened. Butterfly doors are made to rotate open in one direction (usually counterclockwise), and rotate closed in the opposite direction. The door is not equipped with handles, so it is a "push" door. This is for safety, because if it could open in both directions, someone approaching the door might be caught off-guard by someone else opening the other side, thus impacting the first person. Such doors are popular in public transit stations, as it has a large capacity, and when the door is opened, traffic passing in both directions keeps the door open. They are particularly popular in underground subway stations, because they are heavy, and when air currents are created by the movement of trains, the force will be applied to both wings of the door, thus equalizing the force on either side, keeping the door shut. "'French Doors'" derived from an original French design called the casement door, can be created with two out-swinging or in-swinging door panels or two sliding panels or pocket doors. Others. An "'up-and-over'" door is often used in garages. Instead of hinges it has a mechanism, often counterbalanced or sprung, that allows it to be lifted so that it rests horizontally above the opening. Also known as an "'overhead'" door. "'Automatic doors'" are powered open and closed either by power, spring, or both. There are several methods by which an automatic door is activated: In addition to activation sensors automatic doors are generally fitted with safety sensors. These are usually an infrared curtain or beam, but can be a pressure mat fitted on the swing side of the door. The purpose of the safety sensor is to prevent the door from colliding with an object in its path by stopping or slowing its motion. "'Inward opening doors'" are doors that can only be opened (or forced open) from outside a building. Such doors pose a substantial fire risk to occupants of occupied buildings when they are locked. As such doors can only be forced open from the outside, building occupants would be prevented from escaping. In commercial and retail situations manufacturers have included in the design a mechanism that allows an inward opening door to be pushed open outwards in the event of an emergency (which is often a regulatory requirement). This is known as a 'breakaway' feature. Pushing the door outward at its closed position, through a switch mechanism, disconnects power to the latch and allows the door to swing outward. Upon returning the door to the closed position, power is restored. Applications. Doors have numerous general and specialized uses in buildings, storage devices, vehicles, etc. In building interiors, doors are generally used to separate interior spaces, rooms, closets, etc. for privacy, convenience, and safety reasons. Doors are also used to secure passages into a building from the exterior for reasons of safety and climate control. Other than these common usages, doors also have the following applications: Doorway. When framed in wood for snug fitting of a door, the doorway consists of two vertical "jambs" on either side, a "lintel" or "head jamb" at the top, and perhaps a "threshold" at the bottom. When a door has more than one movable section, one of the sections may be called a "leaf". See door furniture for a discussion of attachments to doors such as door handles and doorknobs. Related hardware. Door furniture or hardware refers to any of the items that are attached to a door or a drawer to enhance its functionality or appearance. This includes items such as hinges, handles, door stops, etc. Door construction. Panel doors'" (doors built with frame and panel construction, also called "'stile and rail doors'"): "'Plank and batten doors'", (an older design consisting primarily of vertical slats): "'Ledged and braced doors'" Consists of vertical tongue and grooved boards held together with battens and diagonal braces. "'Frame and filled door'" Consists of a solid timber frame, filled on one face, face with Tongue and Grooved boards. Quite often used externally with the boards on the weather face. "'Flush doors'" (many modern doors, including most interior doors): Door swings, or handing, are always determined from the secure side of the door (ie. the side you use the key on, outside to inside, or public to private). Sizing: A standard US door size 36" x 80" (0.91 m x 2.03 m). Note: In Australia, this is different. The fridge rule applies (you can't stand in a fridge, the door always opens towards you). If the hinges are on the left then its a left hand (or left hung) door. If the hinges are on the right then its a right hand (or right hung) door. See the Australian Standards for Installation of Timber Doorsets, AS 1909-1984 pg 6. History. The earliest records are those represented in the paintings of the Egyptian tombs, in which they are shown as single or double doors, each in a single piece of wood. In Egypt, where the climate is intensely dry, there would be no fear of their warping, but in other countries it would be necessary to frame them, which according to Vitruvius (iv. 6.) was done with stiles (sea si) and rails "(see: Frame and panel)": the spaces enclosed being filled with panels (tympana) let into grooves made in the stiles and rails. The stiles were the vertical boards, one of which, tenoned or hinged, is known as the hanging stile, the other as the middle or meeting stile. The horizontal cross pieces are the top rail, bottom rail, and middle or intermediate rails. The most ancient doors were in timber, those made for King Solomon's temple being in olive wood (I Kings vi. 31-35), which were carved and overlaid with gold. The doors dwelt upon in Homer would appear to have been cased in silver or brass. Besides Olive wood, elm, cedar, oak and cypress were used. All ancient doors were hung by pivots at the top and bottom of the hanging stile which worked in sockets in the lintel and sill, the latter being always in some hard stone such as basalt or granite. Those found at Nippur by Dr. Hilprecht, dating from 2000 B.C. were in dolerite. The tenons of the gates at Balawat were sheathed with bronze (now in the British Museum). These doors or gates were hung in two leaves, each about wide and. high; they were encased with bronze bands or strips, 10 in. high, covered with repouss decoration of figures, etc. The wood doors would seem to have been about 3 in. thick, but the hanging stile was over diameter. Other sheathings of various sizes in bronze have been found, which proves this to have been the universal method adopted to protect the wood pivots. In the Hauran in Syria, where timber is scarce the doors were made in stone, and one measuring by is in the British Museum; the band on the meeting stile shows that it was one of the leaves of a double door. At Kuffeir near Bostra in Syria, Burckhardt found stone doors, 9 to. high, being the entrance doors of the town. In Etruria many stone doors are referred to by Dennis. The ancient Greek and Roman doors were either single doors, double doors, sliding doors or folding doors, in the last case the leaves were hinged and folded back. In Eumachia, is a painting of a door with three leaves. In the tomb of Theron at Agrigentum there is a single four-panel door carved in stone. In the Blundell collection is a bas-relief of a temple with double doors, each leaf with five panels. Among existing examples, the bronze doors in the church of SS. Cosmas and Damiano, in Rome, are important examples of Roman metal work of the best period; they are in two leaves, each with two panels, and are framed in bronze. Those of the Pantheon are similar in design, with narrow horizontal panels in addition, at the top, bottom and middle. Two other bronze doors of the Roman period are in the Lateran Basilica. Heron of Alexandria created the earliest known automatic door in the 1st century AD during the era of Roman Egypt. The first foot-sensor-activated automatic door was made in China during the reign of Emperor Yang of Sui (r. 604–618), who had one installed for his royal library. The first automatic gate operators were later created in 1206 by the Arabic inventor, Al-Jazari. The doors of the church of the Nativity at Bethlehem (6th century) are covered with plates of bronze, cut out in patterns: those of Hagia Sophia at Constantinople, of the 8th and 9th century, are wrought in bronze, and the west doors of the cathedral of Aix-la-Chapelle (9th century), of similar manufacture, were probably brought from Constantinople, as also some of those in St. Marks, Venice. Of the 11th and 12th centuries there are numerous examples of bronze doors, the earliest being one at Hildesheim, Germany (1015). Of others in South Italy and Sicily, the following are the finest: in Sant Andrea, Amalfi (1060); Salerno (1099); Canosa (1111); Troia, two doors (1119 and 1124); Ravello (1179), by Barisano of Trani, who also made doors for Trani cathedral; and in Monreale and Pisa cathedrals, by Bonano of Pisa. In all these cases the hanging stile had pivots at the top and bottom. The exact period when the hinge was substituted is not quite known, but the change apparently brought about another method of strengthening and decorating doors, viz, with wrought-iron bands of infinite varieties of design. As a rule three bands from which the ornamental work springs constitute the hinges, which have rings outside the hanging stiles fitting on to vertical tenons run into the masonry or wooden frame. There is an early example of the 12th century in Lincoln; in France the metal work of the doors of Notre Dame at Paris is perhaps the most beautiful in execution, but examples are endless throughout France and England. Returning to Italy, the most celebrated doors are those of the Battistero di San Giovanni (Florence), which together with the door frames are all in bronze, the borders of the latter being perhaps the most remarkable: the modeling of the figures, birds and foliage of the south doorway, by Andrea Pisano (1330), and of the east doorway by Ghiberti (1425-1452), are of great beauty; in the north door (1402-1424) Ghiberti adopted the same scheme of design for the paneling and figure subjects in them as Andrea Pisano, but in the east door the rectangular panels are all filled, with bas-reliefs, in which Scripture subjects are illustrated with innumerable figures, these being probably the gates of Paradise of which Michelangelo speaks. The doors of the mosques in Cairo were of two kinds; those which, externally, were cased with sheets of bronze or iron, cut out in decorative patterns, and incised or inlaid, with bosses in relief; and those in wood, which were framed with interlaced designs of the square and diamond, this latter description of work being Coptic in its origin. The doors of the palace at Palermo, which were made by Saracenic workmen for the Normans, are fine examples and in good preservation. A somewhat similar decorative class of door to these latter is found in Verona, where the edges of the stiles and rails are beveled and notched. In the Renaissance period the Italian doors are quite simple, their architects trusting more to the doorways for effect; but in France and Germany the contrary is the case, the doors being elaborately carved, especially in the Louis XIV and Louis XV periods, and sometimes with architectural features such as columns and entablatures with pediment and niches, the doorway being in plain masonry. While in Italy the tendency was to give scale by increasing the number of panels, in France the contrary seems to have been the rule; and one of the great doors at Fontainebleau, which is in two leaves, is entirely carried out as if consisting of one great panel only. The earliest Renaissance doors in France are those of the cathedral of St. Sauveur at Aix (1503). In the lower panels there are figures. high in Gothic niches, and in the upper panels a double range of niches with figures about. high with canopies over them, all carved in cedar. The south door of Beauvais Cathedral is in some respects the finest in France; the upper panels are carved in high relief with figure subjects and canopies over them. The doors of the church at Gisors (1575) are carved with figures in niches subdivided by classic pilasters superimposed. In St. Maclou at Rouen are three magnificently carved doors; those by Jean Goujon have figures in niches on each side, and others in a group of great beauty in the center. The other doors, probably about forty to fifty years later, are enriched with bas-reliefs, landscapes, figures and elaborate interlaced borders. In England in the 17th century the door panels were raised with bolection or projecting moldings, sometimes richly carved, round them; in the 18th century the moldings worked on the stiles and rails were carved with the egg and tongue ornament.	The bicycle'", "'bike'", or "'cycle'" is a pedal-driven, human-powered vehicle with two wheels attached to a frame, one behind the other. Bicycles were introduced in the 19th century and now number about one billion worldwide. They are the principal means of transportation in many regions. They also provide a popular form of recreation, and have been adapted for such uses as children's toys, adult fitness, military and police applications, courier services, and competitive sports. The basic shape and configuration of a typical bicycle has changed little since the first chain-driven model was developed around 1885. 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 particular types of cycling. The bicycle has had a considerable effect on human society, in both the cultural and industrial realms. In its early years, bicycle construction drew on pre-existing technologies; more recently, bicycle technology has, in turn, contributed both to old and new areas. History. Multiple 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 (still called push bikes outside of North America), draisines, or hobby horses. Being the first human means of transport to make use of the two-wheeler principle, the draisine (or "mistmashine", "running machine"), invented by the German Baron Karl von Drais, is regarded as the archetype of the bicycle. It was introduced by Drais to the public in Mannheim in summer 1817 and in Paris in 1818. Its rider 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. Another French inventor by the name of Douglas Grasso had a failed prototype of Pierre Lallement's bicycle several years earlier. 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, made of iron and wood, developed into the "penny-farthing" (more formally an "ordinary bicycle", a retronym, since there were then no other kind). It featured a tubular steel frame on which were mounted wire spoked wheels with solid rubber tires. These bicycles were difficult to ride due to their very high seat and poor weight distribution. The "dwarf ordinary" addressed some of these faults by reducing the front wheel diameter and setting the seat further back. This necessitated the addition of gearing, effected in a variety of ways, to attain sufficient speed. Having to both pedal and steer via the front wheel remained a problem. J. K. Starley, J. H. Lawson, and Shergold solved this problem by introducing the chain drive (originated by Henry Lawson's unsuccessful "bicyclette"), connecting the frame-mounted pedals to the rear 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. Further innovations increased comfort and ushered in a second bicycle 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 became widely 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 widespread advertising, production, and use of these devices. Uses. Bicycles have been and are employed for many uses: Technical aspects. The bicycle has undergone continual adaptation and improvement since its inception. These innovations have continued with the advent of modern materials and computer-aided design, allowing for a proliferation of specialized bicycle types. Types. 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, hybrid bicycles, cruiser bicycles, and BMX bicycles. Less common are tandems, lowriders, tall bikes, fixed gear (fixed-wheel), 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". Dynamics. A bicycle stays upright while moving forward by being steered so as to keep its center of gravity over the wheels. 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 in order successfully navigate it. 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. 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 self-powered means of transportation in terms of energy a person must expend to travel a given distance. 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%. 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 traveling on a bicycle at low to medium speeds of around 10-15 mph (15-25 km h), uses 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. 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 supine position or a prone position, thus creating a recumbent bicycle or human powered vehicle. Drag can also be reduced by covering the bicycle with an aerodynamic fairing. 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. 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. Frame. The great majority of today's bicycles have a frame with upright seating which looks much like the first chain-driven bike. 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 frames. 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. 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. Drivetrain and gearing. Since cyclists' legs are most efficient over a narrow range of pedaling speeds (cadence), a variable gear ratio helps a cyclist to maintain an optimum pedalling speed while covering varied terrain. As a first approximation, utility bicycles often use a hub gear with a small number (3 to 5) of widely-spaced gears, road bicycles and racing bicycles use derailleur gears with a moderate number (10 to 22) of closely-spaced gears, while mountain bicycles, hybrid bicycles, and touring bicycles use dérailleur gears with a larger number (15 to 30) of moderately-spaced gears, often including an extremely low gear (granny gear) for climbing steep hills. 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, e.g. it may be comfortable to 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 cycles to maintain a given speed, but with more effort per turn of the pedals. 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 relatively small number of bicycles use a shaft drive to transmit power. A very small number of bicycles (mainly single-speed bicycles intended for short-distance commuting) use a belt drive as an oil-free way of transmitting power. 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 11 sprockets, hub gear built in to 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). With a "shaft drive" transmission, 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. There is some small loss of efficiency due to the two gear sets needed. The only gearing option with a shaft drive is to use a hub gear. 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" "drop" as they curve forward and down, offering the cyclist best braking power from a more aerodynamic "crouched" position, as well as more upright positions in which the hands grip the brake lever mounts, the forward curves, or the upper flat sections for increasingly upright postures. Mountain bikes generally feature a 'straight handlebar' or 'riser bar' with varying degrees of sweep backwards and centimeters rise upwards, as well as wider widths which can provide better handling due to increased leverage against the wheel. 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, 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 men. 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. Brakes. Modern bicycle "brakes" may be "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, "disc brakes", with a separate rotor for braking. Disc brakes are more common on off-road bicycles, tandems and recumbent bicycles than on road-specific bicycles. 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 dedicated 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, the rider applies resistance to the pedals – this acts as a braking system which can be as effective as a friction-based rear wheel brake, but not as effective as a front wheel brake. 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: 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. Wheels. The wheel axle fits into dropouts in the frame and forks. A pair of wheels may be called a wheelset, especially in the context of ready-built "off the shelf", performance-oriented wheels. Tires vary enormously. Skinny, road-racing tires may be completely smooth, or (slick). On the opposite extreme, off-road tires are much wider and thicker, and usually have a deep tread for gripping in muddy conditions. Accessories, repairs, and tools. Some components, which are often optional accessories on sports bicycles, are standard features on utility bicycles to enhance their usefulness and comfort. Mudguards, or fenders, protect the cyclist and moving parts from spray when riding through wet areas and chainguards protect clothes from oil on the chain while preventing clothing from being caught between the chain and crankset teeth. Kick stands keep a bicycle upright when parked. Front-mounted baskets for carrying goods are often used. Luggage carriers and panniers mounted above the rear tire can be used to carry equipment or cargo. Parents sometimes add rear-mounted child seats and or an auxiliary saddle fitted to the crossbar to transport children. "Toe-clips" and "toestraps" and clipless pedals help keep the foot locked in the proper position on the pedals, and enable the cyclist to pull as well as push the pedals—although not without their hazards, eg. may lock foot in when needed to prevent a fall. Technical accessories include cyclocomputers for measuring speed, distance, etc. Other accessories include lights, reflectors, security locks, mirror, water bottles and cages, and bell. Bicycle helmets may help reduce injury in the event of a collision or accident, and a certified helmet is legally required for some riders in some jurisdictions. Helmets are classified as an accessory or an item of clothing by others. Many cyclists carry "tool kits". These may include a tire patch kit (which, in turn, may contain any combination of a hand pump or CO2 Pump, tire levers, spare tubes, self-adhesive patches, or tube-patching material, an adhesive, a piece of sandpaper or a metal grater (to roughing the tube surface to be patched), and sometimes even a block of French chalk.), wrenches, hex keys, screwdrivers, and a chain tool. There are also cycling specific multi-tools that combine many of these implements into a single compact device. More specialized bicycle components may require more complex tools, including proprietary tools specific for a given manufacturer. Some bicycle parts, particularly hub-based gearing systems, are complex, and many cyclists prefer to leave maintenance and repairs to professional bicycle mechanics. In some areas it is possible to purchase road-side assistance from companies such as the Better World Club. Other cyclists maintain their own bicycles, perhaps as part of their enjoyment of the hobby of cycling or simply for economic reasons. The ability to repair and maintain your own bicycle is also celebrated within the DIY movement. Standards. A number of formal and industry standards exist for bicycle components to help make spare parts exchangeable and to maintain a minimum product safety. The International Organization for Standardization, ISO, has a special technical committee for cycles, TC149, that has the following scope: "Standardization in the field of cycles, their components and accessories with particular reference to terminology, testing methods and requirements for performance and safety, and interchangeability." CEN, European Committee for Standardisation, also has a specific Technical Committee, TC333, that defines European standards for cycles. Their mandate states that EN cycle standards shall harmonize with ISO standards. Some CEN cycle standards were developed before ISO published their standards, leading to strong European influences in this area. European cycle standards tend to describe minimum safety requirements, while ISO standards have historically harmonized parts geometry. Parts. For details on specific bicycle parts, see list of bicycle parts and. Social and historical aspects. The bicycle has had a considerable effect on human society, in both the cultural and industrial realms. In daily life. Around the turn of the 20th century, bicycles reduced crowding in inner-city tenements by allowing workers to commute from more spacious dwellings in the suburbs. They also reduced dependence on horses. 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. Recently, several European cities have implemented successful schemes known as community bicycle programs or bike-sharing. These initiatives complement a city's public transport system and offer an alternative to motorized traffic to help reduce congestion and pollution. Users take a bicycle at a parking station, use it for a limited amount of time, and then return it to the same or different station. Examples include Bicing in Barcelona, Vélo'v in Lyon and Vélib' in Paris. In cities where the bicycle is not an integral part of the planned transportation system, commuters often use bicycles as elements of a mixed-mode commute, where the bike is used to travel to and from train stations or other forms of rapid transit. Folding bicycles are useful in these scenarios, as they are less cumbersome when carried aboard. Los Angeles removed a small amount of seating on some trains to make more room for bicycles and wheel chairs. Bicycles offer an important mode of transport in many developing countries. Until recently, bicycles have been a staple of everyday life throughout Asian countries. They are the most frequently used method of transport for commuting to work, school, shopping, and life in general. As a result, bicycles there are almost always equipped with baskets. Female emancipation. 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 embodied, and so the bicycle came to symbolize the New Woman of the late 19th century, especially in Britain and the United States. The bicycle was recognized by 19th-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, untrammeled 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." Male anger at the freedom symbolized by the New (bicycling) Woman was demonstrated when the male undergraduates of Cambridge University showed their opposition to the admission of women as full members of the university by hanging a woman bicyclist in effigy in the main town square. This was as late as 1897. The bicycle craze in the 1890s also 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. Economic implications. 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 aircraft. They also served to teach the industrial models later adopted, including mechanization and mass production (later copied and adopted by Ford and General Motors), vertical integration (also later copied and adopted by Ford), aggressive advertising (as much as 10% of all advertising in U.S. periodicals in 1898 was by bicycle makers), lobbying for better roads (which had the side benefit of acting as advertising, and of improving sales by providing more places to ride), all first practised by Pope. In addition, bicycle makers adopted the annual model change (later derided as planned obsolescence, and usually credited to General Motors), which proved very successful. Furthermore, bicycles were an early example of conspicuous consumption, being adopted by the fashionable elites. In addition, by serving as a platform for accessories, which could ultimately cost more than the bicycle itself, it paved the way for the likes of the Barbie doll. Moreover, they helped create, or enhance, new kinds of businesses, such as bicycle messengers, travelling seamstresses, riding academies, and racing rinks (Their board tracks were later adapted to early motorcycle and automobile racing.) Also, there were a variety of new inventions, such as spoke tighteners, and specialized lights, socks and shoes, and even cameras (such as the Eastman Company's "Poco"). Probably the best known and most widely used of these inventions, adopted well beyond cycling, is Charles Bennett's Bike Web, which came to be called the "jock strap". They also presaged a move away from public transit that would explode with the introduction of the automobile. This liberation would be repeated again with the appearance of the snowmobile. J. K. Starley's company became the Rover Cycle Company Ltd. in the late 1890s, and then simply the Rover Company when it started making cars. The Morris Motor Company (in Oxford) and Škoda also began in the bicycle business, as did the Wright brothers. Alistair Craig, whose company eventually emerged to become the engine manufacturers Ailsa Craig, also started from manufacturing bicycles, in Glasgow in March 1885. 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 Asian companies. For example, some 60% 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. One of the profound economic implications of bicycle use is that it liberates the user from oil consumption (Ballantine, 1972). H.G. Wells said: “Every time I see an adult on a bicycle, I no longer despair for the future of the human race.” (Quotegarden.com). The bicycle is a inexpensive, fast, healthy and environmentally friendly mode of transport (Illich, 1974) Legal requirements. Early in its development, like in the case of automobiles, there were restrictions on the operation of bicycles. Along with advertising, and to gain free publicity, Albert A. Pope litigated on behalf of cyclists The 1968 Vienna Convention on Road Traffic of the United Nations considers a bicycle to be a vehicle, and a person controlling a bicycle (whether actually riding or not) is considered an operator. 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 offense to use a bicycle that is not in roadworthy condition. In most jurisdictions, bicycles must have functioning front and rear lights 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 little noise, some countries insist that bicycles have a warning bell for use when approaching pedestrians, equestrians, and other cyclists. See also. "'Special uses and related vehicle types'" References. Other authors: Eddie Borysewicz, Greg LeMond, Davis Phinney, Connie Carpenter.