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The human
power output to the bike is the product of pedal velocity and pedal force.
The power output curve is, therefore, peaked over some optimal muscle-flexing
range that is related to the velocity of the cyclists feet. The diagram
shows both the maximum force that can be exerted on the pedals as a function
of foot velocity(red) and the corresponding power output.
Matching the
rider power output curve to the needs of a bicycle in covering different types
of terrain requires a gear system. In designing the gear system, the maximum
knee velocity must be taken into account. The blue bar on the diagram
represents a possible foot velocity range that might be used in gear system design.
The impedence match over this blue range is not always optimal (green
zone) but it is still close enough to obtain good performance and permit a
reduced number of gears. |
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