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Shifting to a New Idea
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16595 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
11 / 1989 |
2,401 Words |
| Author
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Jeffrey Hansen
Jeffrey Hansen writes on science and health for the Birmingham
News. |
At a time when many Americans are concerned about reducing our dependence on automobiles to save energy resources and minimize pollution, the venerable bicycle is an attractive, simple alternative. Still a major mode of transportation in Europe, the bicycle, used as a replacement for the automobile, could reduce environmental hazards and make people more healthy as well.
But two-wheelers have a basic defect: Shifting gears is a complex procedure. The rear gear-shifter, or derailleur, of a basic 10-or 12-speed bicycle is a device with imperfections that become obvious on even the most moderate of hilly terrains. If a cyclist misses a downshift on an upgrade, the chain slips, causing the bicycle to wobble to an unintended halt. If the chain slips off the teeth of the gear completely, it must be put back on--a greasy, dirty chore.
Even on flat terrain, shifting intimidates the casual rider. Shifting is an art, like learning how far to slide the arm of a trombone to blow an E flat. "People buy a 10-speed bike and never shift gears," says John Siegwart. They are afraid to."
Siegwart, 32, began thinking of the problem of shifting bicycle gears in 1984, as a design project for his senior year study in mechanical engineering at the University of Alabama at Birmingham. Always mechanically inclined, he has single-handedly invented a new way to shift a bicycle electrically,. His device may simplify the operation of vehicles from wheelchairs and snowmobiles to bulldozers.
The problems of the derailleur--a small, metal arm festooned with two Ritz Cracker-sized gears hanging below the rear axle--are inherent in its design. As the rider tugs the shift lever up or down, the derailleur moves in or out, pushing or pulling the bicycle chain that threads through the two small gears. From the derailleur, the chain feeds onto one of the set of larger gears, or sprockets, that sit together like a stack of pancakes, set on edge, on the side of the rear wheel.
Moving the derailleur bends the chain sideways, like a snake, toward a smaller sprocket in an up shift or to a larger sprocket in a downshift. In the up shift, the chain falls onto the neighboring smaller sprocket. In the downshift, the larger neighboring sprocket has to snag the chain on one of its teeth and pull it up.
The awkwardness of these motions makes shifting gears cumbersome.
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