A bicycle is a human-powered two-wheeled vehicle that converts leg power into forward motion. It is the most efficient means of human transport ever devised, with an average speed more than three times that of walking and nearly as fast as running. Invented in the early 19th century, the bicycle replaced the horse as the primary mode of transportation in many areas and is still a popular form of recreation and sport. Bicycles have many variants for various uses including racing, touring, family riding, commuting, and utility. The bicycle is a complex machine with many moving parts, and it requires regular maintenance to keep it in good working order.
The bicycle was conceived as the first practical device to transform human energy into a vehicle for transportation. It was designed to be much more comfortable than its ancestor, the velocipede de pedale, and able to carry a rider over long distances at reasonable speeds. The word bicycle comes from the French words, bis (twice) and cile (wheel). Historians disagree about who invented the bicycle; Leonardo da Vinci is credited with drawing a sketch of a bicycle in 1492 in his Codex Atlanticus, but this was later discovered to be a forgery.
Karl von Drais Sauerbronn is generally accepted as the inventor of the bicycle, although his design was not practical until it had been improved by others. The improvements made included the addition of a chain and cranks and a rear wheel gear. The gearing allowed the rider to power the bicycle without having to use his or her hands.
Today, the majority of bicycles are manufactured with a diamond frame, which has become the dominant design because it balances strength and comfort. The frame usually consists of a tube made of a high-quality, low-carbon alloy steel such as chromoly or titanium, although carbon fiber frames have recently been introduced in higher-end models.
The wheels of a bicycle consist of a hub (center) with a plethora of spokes that lead to a circular rim fastened to the tire. The tires are filled with air, and they provide traction on surfaces such as dirt, gravel, pavement, snow, and ice. A bicycle’s frame is a critical component because it connects the wheels, seat, and handlebars.
Bicycles have a wide variety of components, including shifters and derailleurs, which control the transfer of power from the cranks to the wheels. They also adjust the wheel diameter, provide steering, and determine the position of the seat.
A bicycle can be equipped with a rack and other attachments for carrying luggage, groceries, tools, or equipment. Other accessories include brakes, lights, mirrors, and fenders. Some bikes have suspension systems to reduce the impact of rough terrain on the rider.
The bicycle is the most widely used mode of transportation in the world, and it is used for recreation, competition, utilitarian purposes, and as a method of getting around town. There are about 1 billion bicycles in the world. In the United States, the bicycle industry employs about 1.7 million people.