Explore the world of bicycles


Bicycle performance

In both biological and mechanical terms, theits efficiency, cycling requires a longer
bicycle is extraordinarily efficient. Indistance, and often greater time, than
terms of the amount of energy a person mustrunning to consume the same amount of energy.
expend to travel a given distance,
investigators have calculated it to be theThe average "in-shape" man can produce about
most efficient self-powered means of3 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 theamateurs producing 5 watts/kg and elite
rider into the pedals is transmitted to theathletes achieving 6 watts/kg for similar
wheels, although the use of gearinglengths of time. Elite track sprinters are
mechanisms may reduce this by 10-15% 2 3. Inable to attain an instantaneous maximum
terms of the ratio of cargo weight a bicycleoutput of around 2,000 watts, or in excess of
can carry to total weight, it is also a most25 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 lowthe end of a five-hour long road race. Even
to medium speeds of around 10-15 mph (16-24at moderate speeds, most cycling energy is
km/h), using only the energy required tospent in overcoming aerodynamic drag, which
walk, is the most energy-efficient means ofincreases 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 theTypical 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 anreasonably fit rider can ride at 50 km/h (30
aerodynamic fairing to achieve very low airmph) 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 requireswith calm winds without external aids (such
about 100 watts to walk at 5 km/h. That sameas motor pacing and wind-blocks) is 130.36 km
man on a bicycle, on the same ground, withh (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/kmDiablo II, a highly aerodynamic recumbent
is roughly one-fifth as much. Generally usedbicycle.
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 bestart with, will have the same effect over a
limited by muscle and knee pain, cycling40 km time trial as removing a protrusion
offers comparable outdoor exercise that caninto the air the size of a pencil. For this
be enjoyed by people of a wide range ofreason more recent designs have concentrated
fitness levels: it is a "no-impact" sporton lowering wind resistance, using
that is easy on the body as long as the bikeaerodynamically shaped tubing, flat spokes on
is properly "fit." In addition, sincethe wheels, and handlebars that allow the
bicycling can also provide convenientrider to bend over into the wind. These
transportation, less self-discipline may bechanges can impact performance dramatically,
required to keep to the activity, since itcutting minutes off a time trial.
has a practical purpose. However, because of



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