The bicycle is a human-powered, two-wheeled, pedal-driven machine for transporting people and things. It is the most efficient means of transportation for a given distance, requiring up to only 10% of the energy required for walking or running. It is used by recreational riders, courier services, and in competitions such as bicycle racing.

The modern bicycle has undergone a number of technical improvements over the years, but its fundamental design has remained the same since about 1900. These refinements include changing materials, improving the frame, adding multiple-speed gears, and increasing the size of the wheel.

Several types of bicycles are available for sale in many markets, including racers’ models, mountain bikes, city/road hybrids, and children’s bikes. Many of these types are designed to meet different needs, and some are more specialized than others.

A bicycle frame is the main skeletal structure of a bike and sets the stage for its ride quality and experience. Its strength, weight, and geometry determine how well the other components (such as the drivetrain and braking system) work together.

Bicycles are a relatively simple machine to maintain, although some parts may require special tools or be difficult to replace without disassembly of the entire bike. Many cyclists choose to perform some or all of their maintenance themselves, which can be easier and less expensive than hiring a mechanic.

Many of the same principles that apply to car manufacturing also apply to the design of a bicycle, so that it is easy for anyone with basic mechanical skills to make repairs. The International Organization for Standardization has a special technical committee for cycles, TC149, which is dedicated to “Standardization in the field of cycles, their components and accessories with particular reference to terminology, testing methods and requirements for performance and safety, and interchangeability.”

Most people who ride a bicycle do so for recreation, exercise, or transport. They may also compete in cycling events, such as races and triathlons. In order to improve their performances, some cyclists use training techniques such as periodization and power-based training.

The bicycle has had a significant impact on human society, both culturally and industrially. During the late 19th and early 20th centuries, it reduced crowding in inner-city tenements and allowed commuters to travel further away from their workplaces. It also reduced dependence on horses for transportation, and made it possible for people to spend more leisure time in rural areas, as a bicycle can travel three or four times faster than walking. It is a popular sport, and an important mode of transport in many cities and countries worldwide. Many individuals own or rent bicycles, and some communities have implemented programs to promote bike commuting. It is a very efficient mode of transportation, especially in urban areas, and can be used to transport large amounts of cargo. In some places, bicycles are more common than cars. For this reason, some governments have adopted policies to promote their usage. They may also have regulations to regulate traffic flow.