Bicycles are one of the world's most popular modes of transportation, with some 800 million bicycles outnumbering cars by two to one. Bicycles are also the most energy-efficient vehicle—a cyclist burns about 35 calories per mile (22 calories per km), while an automobile burns 1,860 calories per mile (1,156 calories per km). Bicycles are used not only for transportation, but for fitness, competition, and touring as well. They come in myriad shapes and styles, including racing bikes, all-terrain bikes, and stationary bicycles, as well as unicycles, tricycles, and tandems.
As far back as 1490, Leonardo da Vinci had envisioned a machine remarkably similar to the modern bicycle. Unfortunately, da Vinci did not attempt to build the vehicle, nor were his sketches discovered until the 1960s. In the late 1700s a Frenchman named Comte de Sivrac invented the Celerifere, a crude wooden hobby horse made of two wheels and joined by a beam. The rider would sit atop the beam and propel the contraption by pushing his or her feet against the ground.
In 1816 the German Baron Karl von Drais devised a steerable hobby horse, and within a few years, hobby-horse riding was a fashionable pastime in Europe. Riders also discovered that they could ride the device with their feet off the ground without losing their balance. And so, in 1840, a Scottish black-smith named Kirkpatrick Macmillan made a two-wheel device that was operated by a treadle. Two years later he traveled as many as 40 miles (64 km) at a stretch during a record 140-mile (225 km) round trip to Glasgow. A couple decades later, a Frenchman, Ernest Michaux, designed a hobby horse that utilized cranks and rotating pedals connected to the front axle. The Velocipede, made with wooden wheels and an iron frame and tires, won the nickname of the "boneshaker."
The 1860s proved to be an important decade for bicycle improvements with the inventions of ball-bearing hubs, metal-spoked wheels, solid rubber tires, and a lever-operated, four-speed gearshift. Around 1866 an unusual version of the Velocipede was created in England by James Stanley. It was called the Ordinary, or Penny Farthing, and it had a large front wheel and a small rear wheel. The Ordinaries were soon exported to the U.S. where a company began to manufacture them as well. These bicycles weighed a hefty 70 pounds (32 kg) and cost $300—a substantial sum at the time.
By 1885, another Englishman, John Kemp Starley, created the Rover Safety, so called since it was safer than the Ordinary which tended to cartwheel the rider over the large front wheel at abrupt stops. The Safety had equally sized wheels made of solid rubber, a chain-driven rear wheel, and diamond-shaped frame. Other important developments in the 1800s included the use of John Boyd Dunlop's pneumatic tires, which had air-filled inner tubes that provided shock absorption. Coaster brakes were developed in 1898, and shortly thereafter freewheeling made biking easier by allowing the wheels to continue to spin without pedaling.
During the 1890s bicycles became very popular, and the basic elements of the modern bicycle were already in place. In the first half of the 20th century, stronger steel alloys allowed thinner frame tubing which made the bicycles lighter and faster. Derailleur gears were also developed, allowing smoother riding. After the Second World War, bicycle popularity slipped as automobiles flourished, but rebounded in the 1970s during the oil crisis. About that time, mountain bikes were invented by two Californians, Charlie Kelly and Gary Fisher, who combined the wide tires of the older balloontire bikes with the lightweight technology of racing bikes. Within 20 years, mountain bikes became more popular than racing bikes. Soon hybrids of the two styles combined the virtues of each.
The Raw Materials
The most important part of the bicycle is the diamond-shaped frame, which links the components together in the proper geometric configuration. The frame provides strength and rigidity to the bicycle and largely determines the handling of the bicycle. The frame consists of the front and rear triangles, the front really forming more of a quadrilateral of four tubes: the top, seat, down, and head tubes. The rear triangle consists of the chainstays, seatstays, and rear wheel dropouts. Attached to the head tube at the front of the frame are the fork and steering tube.
For much of the bicycle's history the frame was constructed of heavy, but strong, steel and alloy steel. Frame material was continually improved to increase strength, rigidity, lightness, and durability. The 1970s ushered in a new generation of more versatile alloy steels which could be welded mechanically, thereby increasing the availability of light and inexpensive frames. In the following decade lightweight aluminum frames became the popular choice. The strongest metals, however, are steel and titanium with life-expectancy spanning decades, while aluminum may fatigue within three to five years.
Advances in technology by the 1990s led to the use of even lighter and stronger frames made of composites of structural fibers such as carbon. Composite materials, unlike metals, are anisotropic; that is, they are strongest along the axis of the fibers. Thus, composites can be shaped into single-piece frames, providing strength where needed.
The components, such as wheels, derailleurs, brakes, and chains, are usually made of stainless steel. These components are generally made elsewhere and purchased by the bicycle manufacturer.
Seamless frame tubes are constructed from solid blocks of steel that are pierced and "drawn" into tubes through several stages. These are usually superior to seamed tubes, which are made by drawing flat steel strip stock, wrapping it into a tube, and welding it together along the length of the tube. Seamless tubes may then be further manipulated to increase their strength and decrease their weight by butting, or altering the thickness of the tube walls. Butting involves increasing the thickness of the walls at the joints, or ends of the tube, where the most stress is delivered, and thinning the walls at the center of the tube, where there is relatively little stress. Butted tubing also improves the resiliency of the frame. Butted tubes may be single-butted, with one end thicker; double-butted, with both ends thicker than the center; triple-butted, with different thicknesses at either end; and quad-butted, similar to a triple, but with the center thinning towards the middle. Constant thickness tubes, however, are also appropriate for certain bikes.
The tubes are assembled into a frame by hand-brazing or welding by machine, the former being a more labor-intensive process and therefore more expensive. Composites may be joined with strong glue or plastic binders. The components are generally manufactured by machine and may be attached to the frame by hand or machine. Final adjustments are made by skilled bicycle builders.
Assembling the Frame
Tailoring the tubes
- 1 The metal is annealed, or softened by heating, and hollowed out to form "hollows," or "blooms." These are heated again, pickled in acid to remove scale, and lubricated.
- 2 The hollows are measured, cut, and precision mitered to the appropriate dimensions. Frame sizes for adult bicycles generally run from 19-25 inches (48-63 cm) from the top of the seat post tube to the middle of the crank hanger.
- 3 Next, the hollows are fitted over a mandrel, or rod, attached to a draw bench. To achieve the right gauge, the hollows pass through dies which stretch them into thinner and longer tubes, a process called cold drawing.
- 4 The tubes may be shaped and tapered into a variety of designs and lengths. The taper-gauge fork blades may have to pass through more than a dozen operations to achieve the correct strength, weight, and resilience.
Brazing, welding, and gluing
- 5 Tubes can be joined into a frame either by hand or machine. Frames may be brazed, welded, or glued, with or without lugs, which are the metal sleeves joining two or more tubes at a joint. Brazing is essentially welding at a temperature of about 1600°F (871°C) or lower. Gas burners are arranged evenly around the lugs which are heated, forming a white flux that melts and cleans the surface, preparing it for brazing. The brazing filler is generally brass (copper-zinc alloy) or silver, which melt at lower temperatures than the tubes being joined. The filler is applied and as it melts, it flows around the joint, sealing it.
Aligning and cleaning
- 6 The assembled frames are placed into jigs and checked for proper alignment. Adjustments are made while the frame is still hot and malleable.
- 7 The excess flux and brazing metals are cleaned off by pickling in acid solutions and by washing and grinding the brazing until it is smooth.
- 8 After the metals have cooled, further precision alignments are made.
- 9 The frames are painted, not only to create a more finished appearance, but also to protect the frame. The frame is first primed with an undercoat and then painted with a colored enamel. Paint may be applied by hand-spraying or by passing the frames through automatic electrostatic spraying rooms. The negatively charged frames attract the positively charged paint spray as the frames rotate for full coverage. Finally, transfers and lacquer are applied to the frame. Chrome plating may also be used instead of paint on components such as the fork blades.
Derailleurs and gear shift levers
- 10 Depending on the style of bicycle, the gear shift levers are mounted either on the down tube—popular on racing bikes—on the stem, or on the handlebar ends. A cable is attached, which extends to the front and rear derailleurs. Front derailleurs, which move the chain from one drive sprocket to another, may be clamped or brazed onto the seat tube. Rear derailleurs may be mounted with bolt-on hangers or integral hangers.
Handlebars, stems, and headsets
- 11 Handlebars may be raised, flat, or I dropped. They are bolted to the bicycle stem which is then fitted into the head tube. The headset components, including bearings, cups, and locknuts, are attached to the head tube. The headset allows the fork to turn inside the head tube and thus makes steering easier.
- 12 The brake levers are mounted to the handlebars. Cables extend to the brakes and are fastened to the calipers. Tape, made of plastic or cloth, can then be attached to the handlebars and the ends are plugged.
Saddles and seat posts
- 13 Seat posts are generally steel or aluminum alloy and are bolted or clamped into position. The saddle is generally made of molded padding and covered with nylon or plastic materials. Although leather was the norm for saddles for a long time, it is less commonly used today.
- 14 The crankset supports the pedals and transfers power from the pedals to the chain and rear wheel. Cranksets consist of steel or aluminum alloy crank arms, chain rings, and the bottom bracket assembly of axle, cups, and bearings. They are attached with bolts and caps into the bottom bracket of the bicycle frame. The pedals are then screwed to the ends of the crank arms.
Wheels, tires, and hubs
- 15 Wheel manufacturers conform to the A J International Standards Organization (ISO) system for wheel diameter and tire sizes. Wheels may be constructed by machines, which roll steel strips into hoops that are welded into rims. The rims are drilled to accept spokes, which are laced one round at a time between the rim and hub flange.
- 16 A wheel must be trued, or straightened, in radial and lateral directions to achieve uniform tension. Next, the rim liner, tire, and inner tube are attached. The chain may also be fitted onto the bicycle.
- 17 Rear wheels are fitted with a free-/ wheel, consisting of several cogs and spacers, which frees the rear wheel from the crank mechanism when the rider stops pedaling.
- 18 Wheels are attached to the bicycle frame by means of an axle which runs through the hub of the wheel. The axle may be tightened with bolts at the ends or with quick-release skewers.
The future for bicycles looks promising as we approach the 20th century. Developments in bicycle technology in the 1990s have led to advances in human-powered vehicles (HPVs) design. Most HPVs are low-slung recumbents, which are more aerodynamic than conventional bicycles and therefore reduce drag and increase speed. Recumbents are also safer, and many provide cargo room and weather protection. A hybrid of the bicycle and automobile called the Ecocar began to surface on European streets by the 1990s. Designed by a Dutch surgeon, Wim Van Wijnen, it provided weather protection, safety, luggage room, easy maintenance, comfort, and speed.
The use of computer technology greatly enhanced the design capabilities of manufacturers and designers. Designers are able to simulate various forces working on the bicycle, such as pedaling and road shock. Computer-generated programs make testing simpler, and variations of designs are modified more easily and quickly.
Where To Learn More
Ballantine, Richard and Richard Grant. Richards' Ultimate Bicycle Book. Dorling Kindersley, 1992.
The Bicycle Builder's Bible. TAB Books Inc., 1980.
Bicycle Magazine's Complete Guide to Bicycle Maintenance and Repair, revised ed. Rodale Press, 1990.
Watson, Roderick and Martin Gray. The Penguin Book of the Bicycle, Allen Lane Pub., 1978.
Brown, Stuart F. "The Anybody Bike." Popular Science, August 1991, pp. 58-59, 89.
Schwartz, David M. "Over Hill, Over Dale, On a Bicycle Built for…Goo." Smithsonian, June 1994, pp. 74-86.
Soviero, Marcelle M. "Easy Riders." Popular Science, May 1993, pp. 84-87.
— Audra Avizienis