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Every
cyclist has to overcome wind resistance. Most recreational
cycles in which the rider sits up have very poor aerodynamics.
While newer cycles are being designed with better aerodynamics
in mind, the human body is simply not well designed to slice
through the air. Cycle racers are aware of the problem of wind
resistance and over the years have developed techniques for reducing
it. Cycle designers and inventors have experimented in developing
alternative cycle designs and HPVs (human- powered vehicles)
with an emphasis on better aerodynamic performance.
Wind Resistance
Every cyclist who has ever pedaled
into a stiff headwind knows about wind resistance. It's exhausting!
In order to move forward,
the cyclist must push through the mass of air in front of them.
This takes energy. Aerodynmaic efficiency - a streamlined shape
that cuts through the air more smoothly - enables a cyclist to
travel much faster, with less effort. But the faster the cyclist
goes, the more wind resistance he experiences, and the more energy
he must exert to overcome it. When racing cyclists aim to reach
high speeds, they focus not only on greater power, which has
its human limitations, but also on greater aerodynamic efficiency.
Aerodynamic
drag consists of two forces: air pressure drag and direct friction
(also known as surface friction or skin friction).
A blunt, irregular object disturbs the air flowing around it,
forcing the air to separate from the object's surface. Low pressure
regions from behind the object result in a pressure drag against
the object. With high pressure in the front, and low pressure
behind, the cyclist is literally being pulled backwards. Streamlined
designs help the air close more smoothly around these bodies
and reduce pressure drag. Direct friction occurs when wind comes
into contact with the outer surface of the rider and the cycle.
Racing cyclists often wear "skinsuits" in order to
reduce direct friction. Direction friction is less of a factor
than air pressure drag.
On a flat road, aerodynamic drag
is by far the greatest barrier to a cyclist's speed, accounting
for 70 to 90 percent of the
resistance felt when pedaling. The only greater obstacle is climbing
up a hill: the effort needed to pedal a bike uphill against the
force of gravity far outweighs the effect of wind resistance.
Reducing resistance
Frame builders and designers have
been working on creating more aerodynamically efficient designs.
Some recent designs have
concentrated on shifting from round tubes to oval or tear-shaped
tubes. There is a delicate balancing act between maintaining
a good strength-to-weight ratio while improving aerodynamic
efficiency. Improvements to wheels have made perhaps the biggest
impact. A standard spoked wheel has been described as an "egg
beater," creating many small eddies as the tyre rotates--creating
drag. Disc wheels, while generally heavier than their spoked
counterparts, produce less wind drag and turbulence when they
spin.
While improvements to frames and components
have improved aerodynamic performance, the cyclist is the largest
obstacle to dramatic
improvement. The human body is not very streamlined. Body positioning
is important; road cyclists use "drop bars" to allow
themselves to reduce their frontal area, which helps reduce the
amount of resistance they must overcome. Reducing the frontal
area helps riders increase their speed and their efficiency over
time. In addition to positioning, small details like clothing
can also make a big difference in reducing "skin friction." Tight-fitting
synthetic clothing is worn by almost every professional rider,
both road and mountain. Many recreational riders are also wearing
cycle clothes for the improvement in aerodynamics as well as
comfort.
Drafting
Drafting is an important technique in road racing. Exploratorium
Senior Scientist Paul Doherty explained, "The cyclist,
as he moves through the air, produces a turbulent wake behind
himself. It makes vortices. The vortices actually make a low
pressure area behind the cyclist and an area of wind that
moves along with the cyclist. If you're a following a cyclist
and can move into the wind behind the front cyclist, you
can gain an advantage. The low pressure moves you forward and
the eddies push you forward."
Suprisingly
drafting not only helps the cyclist following the leader,
but the lead cyclist
gains
an advantage as well.
Paul explained, "The interesting thing is by filling in
her eddy you improve the front person's performance as well.
So two people who are drafting can put out less energy than two
individuals (who are not drafting) would covering the same distance
in the same time." While the lead cyclist gains some advantage
in this situation she still needs to expend much more energy
than the cyclist who is following.
In road racing, cyclists
group together in a pack known as the "peloton" or
a pace line called an "echelon." Cyclists
who are part of the group can save up to 40 percent in energy
expeditures over a cyclist who is not drafting with the group.
To be effective drafting, a cyclist needs to be as close as possible
to the cycle in front of him. Many professional cyclists get
within inches of the the cycle in front of them. The shorter
the distance the larger the decrease in wind resistance.
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