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.¹ 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% ^{2 3}. 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. This racing bicycle is built using lightweight, shaped aluminium tubing and carbon fiber stays and forks. ... A bicycle pedal provides the connection between the cyclists foot or shoe and the crankarm allowing the leg to be used to turn the crank. ... The front wheel from a racing bicycle made using a Mavic rim A bicycle wheel is a wheel designed for a bicycle. ... Bicycle gearing is concerned with the connection between the pedals and the rear wheel of a bicycle, and with the effect this connection has on how easy or hard it is to turn the pedals. ...

A human being travelling 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 increasingly higher power outputs relative to speed. A bicycle in which the rider lies in a prone position is referred to as a recumbent bicycle or, if covered in an aerodynamic fairing to achieve very low air drag, as a streamliner. Tandem recumbent bicycle manufactured by BikeE Two short-wheelbase recumbents in an amateur HPV race A recumbent bicycle is a variety of bicycle which places the rider in a seated or supine position (rarely, in a prone position). ... A streamliner is a vehicle that incorporates streamlining to produce a shape that provides less resistance to air, and is more pleasing to the eye. ...

Racing bicycles have dropped handlebars, a narrow seat, and minimal accessories.

On firm, flat, ground, a 70 kg man requires about 100 watts to walk at 5 km/h. That same man on a bicycle, on the same ground, with the same power output, can average 25 km/h, so energy expenditure in terms of kcal/kg/km is roughly one-fifth as much. Generally used figures are I took this picture March 30, 2004--only modification is cropping. ... I took this picture March 30, 2004--only modification is cropping. ... The watt (symbol: W) is the SI derived unit of power. ...

• 1.62 kJ/(km∙kg) or 0.28 kcal/(mile∙lb) for cycling,
• 3.78 kJ/(km∙kg) or 0.653 kcal/(mile∙lb) for walking/running,
• 16.96 kJ/(km∙kg) or 2.93 kcal/(mile∙lb) for swimming.

For many people whose running might be limited by muscle and knee pain, cycling offers comparable outdoor exercise that can be enjoyed by people of a wide range of fitness levels: it is a "no-impact" sport that is easy on the body as long as the bike is properly "fit." In addition, since bicycling can also provide convenient transportation, less self-discipline may be required to keep to the activity, since it has a practical purpose. However, because of its efficiency, cycling requires a longer distance, and often greater time, than running to consume the same amount of energy.

The average "in-shape" man can produce about 3 watts/kg for more than an hour (e.g., around 200 watts for a 70 kg rider), with top amateurs producing 5 watts/kg and elite athletes achieving 6 watts/kg for similar lengths of time. Elite track sprinters are able to attain an instantaneous maximum output of around 2,000 watts, or in excess of 25 watts/kg; elite road cyclists may produce 1,600 to 1,700 watts as an instantaneous maximum in their burst to the finish line at the end of a five-hour long road race. Even at moderate speeds, most cycling energy is spent in overcoming aerodynamic drag, which increases with the square of speed; therefore, power needs increase approximately with the cube of speed. It has been suggested that Drag equation be merged into this article or section. ...

Typical speeds for bicycles are 16 to 32 km/h (10 to 20 mph). On a fast racing bicycle, a reasonably fit rider can ride at 50 km/h (30 mph) on flat ground for short periods. The highest speed ever officially recorded for any human-powered vehicle on level ground and with calm winds without external aids (such as motor pacing and wind-blocks) is 130.36 km/h (81.00 mph). That record was set in 2002 by Canadian Sam Whittingham with the Varna Diablo II, a highly aerodynamic recumbent bicycle. Kilometre per hour (American spelling: kilometer per hour) is a unit of both speed (scalar) and velocity (vector). ... Miles per hour is a unit of speed, expressing the number of international miles covered per hour. ... An aluminum racing bicycle made by Raleigh and built using Shimano components. ... Three human powered vehicles: the Gossamer Albatross II and two bicycles. ... Sam Whittingham and his Varna Diablo Sam Whittingham is a Canadian cyclist who has held several world records on recumbent bicycles. ...

There has been major corporate competition to lower the weight of racing bikes through the use of advanced materials and components. Additionally, advanced wheels are available with low-friction bearings and other features to lower road resistance. In measured tests these components have almost no effect on cycling performance. For instance, lowering a bike's weight by 1 kg, a major effort considering they may weigh less than 15 kg to start with, will have the same effect over a 40 km time trial as removing a protrusion into the air the size of a pencil. For this reason more recent designs have concentrated on lowering wind resistance, using aerodynamically shaped tubing, flat spokes on the wheels, and handlebars that allow the rider to bend over into the wind. These changes can impact performance dramatically, cutting minutes off a time trial. In many racing sports an athlete (or occasionally a team of athletes) will compete in a time trial against the clock to secure the fastest time. ...

Notes

• 1 "Bicycle Technology", S.S. Wilson, Scientific American, March 1973
• 2 "Johns Hopkins Gazette", Aug.30, 1999
• 3 See Chapter 9 of "Bicycling Science" (Reference, below) for details of transmission efficiency.