A bicycle is a two-wheeled human-powered land vehicle with a seat, handlebars, and pedals. It is propelled by the rider pushing down on the pedals, which in turn cause the wheels to spin. A chain connects the pedals to the rear wheel, which is driven by a crank connected to the chain. A bicycle is designed to be easy to operate and relatively safe. It is used for transportation, recreation, and competitive sports. It is also a symbol of freedom and adventure.
Historians do not agree on the exact date of the bicycle’s invention. Leonardo da Vinci is often credited with sketching one in his Codex Atlanticus, but this drawing may be a forgery. It is likely that the bicycle evolved from its ancestor, the velocipede de pedale. Inventors added pedals to the front wheel of this cumbersome device in the 1860s, allowing riders to move more quickly while maintaining control. This invention led to further improvements, including the introduction of gears and hand brakes.
While the frame of a bicycle provides strength, it also sets the stage for how well the other parts will function. For this reason, the frame is sometimes considered to be the most important component of a bicycle. Many different styles of frames are available, from simple aluminum alloy to complex carbon fiber. The selection of materials for a frame is based on a combination of performance requirements and personal preferences.
Bicycles can be fitted with a variety of accessories to increase their functionality and enjoyment. They can be equipped with baskets to carry goods and flowers, or with mudguards for protection from rain. Some have a rear-mounted rack to hold luggage, while others can be equipped with hitches to tow trailers for cargo or children.
The International Organization for Standardization has a technical committee, TC149, which develops standards for cycles and their components and accessories. The committee’s goal is to develop standardized terminology, movement specifications, formal specifications and requirements for performance and safety, and interchangeability of parts.
Whether they are used for exercise, competition or simply to get around town, most bicycles require regular maintenance. Many bicycle owners prefer to do the maintenance themselves rather than take their bikes to a professional mechanic. The maintenance requires knowledge of the mechanical aspects of a bicycle, as well as the use of tools specific to the manufacturer.
When riding a bicycle on public roads, cyclists should obey traffic laws. They should yield to cars and pedestrians, especially at intersections. Cyclists should use bike lanes when available to avoid being struck by faster vehicles. At red lights, they should position themselves in the center of the left turn lane to ensure that motorists see them and have enough time to safely maneuver. Drivers should always look to the right and behind before turning left, and should never pass a bicyclist when they can’t do so safely. They should also reduce their speed for road conditions and drive defensively to protect themselves from collisions with other motorists.