THE BICYCLE IS A TWO-WHEELED, light-weight machine, which is propelled by human power. It is efficient, cheap, easily manufactured, and one of the world’s most popular forms of transportation. The first pedal-driven bicycle was built in Scotland in 1839. Since then the basic design—of a frame, wheels, brakes, handlebars, and saddle—has been gradually improved, with the addition of a chain, gear system, and pneumatic tires (tires inflated with air). The recent invention
of the mountain bike (all-terrain bike) has been an important development. With its strong, rugged frame, wide tires, and 21 gears, a mountain bike enables riders to reach rough and hilly areas that were previously inaccessible to cyclists.
