Alan Cochran, age 12, of Laconia, N.H. for his question:
WHAT DO BICYCLE GEARS DO?
A bicycle is a conveyance with two wheels mounted one behind the other on a metal frame. The rider supplies the vehicle power by pushing two pedals around in a circle with his feet. Gears on a bicycle enable the rider to choose the most efficient combination of pedaling effort and pedhling speed.
Multispeed bicycles have gears that make pedaling easier for the rider at certain times. A rider shifts into a low gear, for example, when going up a hill or riding against the wind. This makes pedaling easier, but it also slows him down unless he pedals faster.
The rider uses a high gear for maximum speed on level surfaces. This enables him to pedal slower, but it also makes pedaling more difficult.
The gears of a multispeed bike are sprockets of different sizes. The number of gears a bicycle has determines its range of speed.
A five speed bicycle has five gears on its rear wheel. A 10 speed bicycle has five gears on its rear wheel and two gears that form the chainwheei. The combination of these front and rear gears gives the bike its 10 speeds.
The rider shifts gears on a three speed middleweight bicycle by moving a lever on the bike's handle bar.
On 10 and 15 speed bicycles, a mechanism called a derailleur shifts or "derails" the chain from one gear to another. On most bicycles with deraiileur gears, the rider shifts gears by moving two levers on the bike's down tube. Some bikes have gear controls in the handle bars.
When the rider pushes the pedals of a bicycle, they turn a sprocket or toothed wheel called a chainwheel. A chain fits over the metal teeth around the edge of the chainwheel. The chain extends to a smaller sprocket on the rear wheel of the bicycle and fits over the teeth of this sprocket. As the large sprocket turns, it moves the chain which turns the small sprocket.
Manufacturers make three main styles of bicycles: lightweight, middleweight and specialty bicycles.
Speciality bicycles include the high riser, popular with riders from 10 to 15 years old. It has high rise handle bars and a seat shaped somewhat like a banana. Many high risers have three or five speed gears.
Lightweight bicycles include both racing and touring models. These bikes are built for speed and easy handling. Most models have gear systems that enable the rider to pedal at different speeds. Most models have five, 10 or 15 speeds. For touring, many riders prefer bikes with 15 speeds.
Middleweight bicycles have heavier wheels and wider, softer tires than lightweights. Some have three or five speeds. Their sturdiness makes them ideal for young children.
Most middleweights weigh from 35 to 45 pounds. Racking lightweight bicycles weigh about 21 pounds.