Explore the world of bicycles


Bicycle performance

In both biological and mechanical terms,than running to consume the same amount
the bicycle is extraordinarilyof energy.
efficient. In terms of the amount ofThe average "in-shape" man can produce
energy a person must expend to travel aabout 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 efficientrider), with top amateurs producing 5
self-powered means of transportation.1watts/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 riderElite track sprinters are able to attain
into the pedals is transmitted to thean instantaneous maximum output of
wheels, although the use of gearingaround 2,000 watts, or in excess of 25
mechanisms may reduce this by 10-15% 2watts/kg; elite road cyclists may
3. In terms of the ratio of cargo weightproduce 1,600 to 1,700 watts as an
a bicycle can carry to total weight, itinstantaneous maximum in their burst to
is also a most efficient means of cargothe finish line at the end of a
transportation.five-hour long road race. Even at
A human being travelling on a bicycle atmoderate speeds, most cycling energy is
low to medium speeds of around 10-15 mphspent in overcoming aerodynamic drag,
(16-24 km/h), using only the energywhich increases with the square of
required to walk, is the mostspeed; therefore, power needs increase
energy-efficient means of transportapproximately with the cube of speed.
generally available. Air drag, whichTypical 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 powerbicycle, a reasonably fit rider can ride
outputs relative to speed. A bicycle inat 50 km/h (30 mph) on flat ground for
which the rider lies in a prone positionshort periods. The highest speed ever
is referred to as a recumbent bicycleofficially recorded for any
or, if covered in an aerodynamic fairinghuman-powered vehicle on level ground
to achieve very low air drag, as aand with calm winds without external
streamliner.aids (such as motor pacing and
On firm, flat, ground, a 70 kg manwind-blocks) is 130.36 km/h (81.00 mph).
requires about 100 watts to walk at 5 kmThat record was set in 2002 by Canadian
h. That same man on a bicycle, on theSam Whittingham with the Varna Diablo
same ground, with the same power output,II, a highly aerodynamic recumbent
can average 25 km/h, so energybicycle.
expenditure in terms of kcal/kg/km isThere has been major corporate
roughly one-fifth as much. Generallycompetition to lower the weight of
used figures areracing 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 beinstance, lowering a bike's weight by 1
limited by muscle and knee pain, cyclinglb, a major effort considering they may
offers comparable outdoor exercise thatweigh less than 15 lb to start with,
can be enjoyed by people of a wide rangewill 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 longthe air the size of a pencil. For this
as the bike is properly "fit." Inreason more recent designs have
addition, since bicycling can alsoconcentrated on lowering wind
provide convenient transportation, lessresistance, using aerodynamically shaped
self-discipline may be required to keeptubing, flat spokes on the wheels, and
to the activity, since it has ahandlebars that allow the rider to bend
practical purpose. However, because ofover into the wind. These changes can
its efficiency, cycling requires aimpact performance dramatically, cutting
longer distance, and often greater time,minutes off a time trial.



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