SCIENCE CONCEPT:
- The rider accounts for 65% to 80% of the drag.
Therefore, the rider's position is very important to the overall
aerodynamics of a bicycle and rider. The importance of rider position
has been known for a long time. The crouched racing position and the
drop handlebars have been used since the 1890's.
STUDENT OBJECTIVE:
- The student will demonstrate and observe the
importance of the position of the rider on a bicycle in relationship to
speed and air resistance.
OVERVIEW:
- The student will sit in various positions on the bicycle and
be timed to see how the rider position influences the speed of the cycle
at the same distance. The effect of wearing a helmet will also be
studied in relationship to the aerodynamic speed.
TEACHER TEXT:
- By looking at a bicycle and rider, there are several
areas for aerodynamic improvement. The most important area is with the
rider position. Aerodynamic improvements can also be made for the frame,
wheels, and individual components.
The rider accounts for 65% to 80% of the drag. Therefore,
the rider's position is very important to the overall aerodynamics of a
bicycle and rider. The importance of rider position has been known for a
long time. The crouched racing position and the drop handlebars have
been used since the 1890's. Still, advances have been made through the
use of testing techniques such as coast down tests and the wind tunnel.
Coast down testing used the velocity at the end of a ramp of known
geometry to determine the drag. By utilizing coast down testing,
researchers have shown that proper body position can reduce drag by 31%
over an upright riding position.
The most aerodynamic position is obtained by using the
hill-descent position where the hands are on the center of the bars. In
this position the elbows are tucked in and the chin is on the hands.
Also, the cranks are at 90 degrees and knees are squeezed into the top
tube. While being very aerodynamically efficient, the hill-descent
position doesn't allow for efficient riding. For efficient riding, the
drag is reduced by 25% by assuming a crouched position with a flat back.
New handlebars have allowed riders to achieve an optimal
aerodynamic position while still allowing for efficient pedaling. These
handlebars allow the rider to achieve the same effect as the hill descent
position while still allowing the rider to pedal efficiently. A helmet
can also help the decrease the aerodynamic drag that a bicyclist
encounters. An aerodynamic bicycle helmet reduces the drag by
approximately 2% over a rider with no helmet. In fact, modern
aerodynamic helmets result in a lower drag even for a bald bicyclists.
Therefore, the right helmet not only protects your head, but can also
give you a competitive edge in a bicycle race.
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PREPARATION TIME:
- 15 minutes.
LESSON TIME:
- 60 minutes.
TEACHER PREP:
- Gather materials
WORDS TO KNOW:
- drag
- aerodynamics
- hill-descent position
- crouched racing position
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