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