A bicycle is a two-wheeled steerable machine, powered by the legs, that can be used for recreation and transport. Its name is derived from the Greek words for “two” and “wheel.” Bicycles can be ridden on smooth surfaces, such as pavement and dirt roads, or on rough terrain, such as paths through woodlands or beaches. There are many different kinds of bicycles, each designed for a particular use or for a particular rider type. For example, a racing bicycle has a very lightweight frame and high-tech components to make it fast and responsive. A touring bike is built to carry a heavy load over long distances.
There are also recreational bikes, such as cruisers and mountain bikes, which are suited to leisurely rides on smooth roads or trails. Bicycles can also be used as a means of transport in cities, where they are preferred over cars because they are quieter and cause less pollution.
The basic bicycle consists of a frame with two wire-spoked wheels, one behind the other. A person sits on the saddle-like seat and steers by leaning and turning handlebars attached to a rotatable fork. His or her feet turn pedals connected to cranks, which drive a chainwheel and sprocket on the rear wheel. The power transferred from the pedals is converted into speed by friction between the tires and the road surface. The result is a vehicle that can be ridden at speeds up to 16-24 km (10-15 miles) per hour–four to five times as fast as walking.
The earliest known predecessors of the modern bicycle were called velocipedes. No one inventor is credited with the creation of the modern bicycle, which first appeared in Europe in the early 1860s and quickly replaced the velocipede. There is some evidence that French mechanic Pierre Lallement applied the concept of pedals to the front wheel of a velocipede in mid-1863; this version was dubbed a penny-farthing because of its size disparity between the front and rear wheels, and it was a huge success.
More than a century later, the bicycle is the most common mode of transportation in much of the world. It is also an important sport and form of recreation, with the world’s most popular race, the Tour de France, drawing millions of spectators each year. The bicycle is easy to learn to operate and can provide a good workout for its riders.
There are now more kinds of bicycles than ever before, as designers continue to find new ways to make them faster, lighter, more reliable, and easier to maintain. In addition to the traditional upright models, there are now recumbent bicycles, which offer greater stability and comfort, as well as electric motor-assisted versions that allow people with limited lower-body mobility to pedal. Some riders prefer a hybrid model that offers the advantages of both upright and recumbent bikes, while others choose a trike with a conventional bicycle front end paired to two side-by-side wheels in the back (also called tadpole). There are even models for people with nerve, skeletal, or muscle problems that prevent them from riding an upright bike.