| In both biological and mechanical terms, the | | | | its efficiency, cycling requires a longer |
| bicycle is extraordinarily efficient. In | | | | distance, and often greater time, than |
| terms of the amount of energy a person must | | | | running to consume the same amount of energy. |
| expend to travel a given distance, | | | | |
| investigators have calculated it to be the | | | | The average "in-shape" man can produce about |
| most efficient self-powered means of | | | | 3 watts/kg for more than an hour (e.g., |
| transportation.1 From a mechanical viewpoint, | | | | around 200 watts for a 70 kg rider), with top |
| up to 99% of the energy delivered by the | | | | amateurs producing 5 watts/kg and elite |
| rider into the pedals is transmitted to the | | | | athletes achieving 6 watts/kg for similar |
| wheels, although the use of gearing | | | | lengths of time. Elite track sprinters are |
| mechanisms may reduce this by 10-15% 2 3. In | | | | able to attain an instantaneous maximum |
| terms of the ratio of cargo weight a bicycle | | | | output of around 2,000 watts, or in excess of |
| can carry to total weight, it is also a most | | | | 25 watts/kg; elite road cyclists may produce |
| efficient means of cargo transportation. | | | | 1,600 to 1,700 watts as an instantaneous |
| | | | maximum in their burst to the finish line at |
| A human being travelling on a bicycle at low | | | | the end of a five-hour long road race. Even |
| to medium speeds of around 10-15 mph (16-24 | | | | at moderate speeds, most cycling energy is |
| km/h), using only the energy required to | | | | spent in overcoming aerodynamic drag, which |
| walk, is the most energy-efficient means of | | | | increases with the square of speed; |
| transport generally available. Air drag, | | | | therefore, power needs increase approximately |
| which increases with the square of speed, | | | | with the cube of speed. |
| requires increasingly higher power outputs | | | | |
| relative to speed. A bicycle in which the | | | | Typical speeds for bicycles are 16 to 32 km/h |
| rider lies in a prone position is referred to | | | | (10 to 20 mph). On a fast racing bicycle, a |
| as a recumbent bicycle or, if covered in an | | | | reasonably fit rider can ride at 50 km/h (30 |
| aerodynamic fairing to achieve very low air | | | | mph) on flat ground for short periods. The |
| drag, as a streamliner. | | | | highest speed ever officially recorded for |
| | | | any human-powered vehicle on level ground and |
| On firm, flat, ground, a 70 kg man requires | | | | with calm winds without external aids (such |
| about 100 watts to walk at 5 km/h. That same | | | | as motor pacing and wind-blocks) is 130.36 km |
| man on a bicycle, on the same ground, with | | | | h (81.00 mph). That record was set in 2002 by |
| the same power output, can average 25 km/h, | | | | Canadian Sam Whittingham with the Varna |
| so energy expenditure in terms of kcal/kg/km | | | | Diablo II, a highly aerodynamic recumbent |
| is roughly one-fifth as much. Generally used | | | | bicycle. |
| figures are | | | | |
| | | | There has been major corporate competition to |
| 1.62 kJ/(km•kg) or 0.28 kcal/(mile•lb) | | | | lower the weight of racing bikes through the |
| for cycling, | | | | use of advanced materials and components. |
| | | | Additionally, advanced wheels are available |
| 3.78 kJ/(km•kg) or 0.653 kcal/(mile•lb) | | | | with low-friction bearings and other features |
| for walking/running, | | | | to lower road resistance. In measured tests |
| | | | these components have almost no effect on |
| 16.96 kJ/(km•kg) or 2.93 kcal/(mile•lb) | | | | cycling performance. For instance, lowering a |
| for swimming. | | | | bike's weight by 1 lb, a major effort |
| | | | considering they may weigh less than 15 lb to |
| For many people whose running might be | | | | start with, will have the same effect over a |
| limited by muscle and knee pain, cycling | | | | 40 km time trial as removing a protrusion |
| offers comparable outdoor exercise that can | | | | into the air the size of a pencil. For this |
| be enjoyed by people of a wide range of | | | | reason more recent designs have concentrated |
| fitness levels: it is a "no-impact" sport | | | | on lowering wind resistance, using |
| that is easy on the body as long as the bike | | | | aerodynamically shaped tubing, flat spokes on |
| is properly "fit." In addition, since | | | | the wheels, and handlebars that allow the |
| bicycling can also provide convenient | | | | rider to bend over into the wind. These |
| transportation, less self-discipline may be | | | | changes can impact performance dramatically, |
| required to keep to the activity, since it | | | | cutting minutes off a time trial. |
| has a practical purpose. However, because of | | | | |