A bicycle is a human-powered machine that converts the energy of its rider into forward motion and kinetic energy to help it glide along a path. Whether used for recreation, transportation or sport, it is the most efficient machine yet devised to transform human energy into motion and transport people over long distances with minimal effort.

Bicycles have changed the way people work, play and live. They have reduced crowding in inner city tenements, allowed workers to commute to suburban jobs and ushered in the era of personal transportation. They have also helped to improve health by reducing dependence on cars and public transit.

It’s hard to say who first conceived of the idea for a two-wheeled bike with pedals and a handlebar, because a number of individuals independently invented similar machines in the 18th century. But in mid-1863 Pierre Lallement incorporated some of the earliest pedals in an improved version of his velocipede de pedale. This was the first bicycle that could be considered a bicycle in the modern sense of the word, and it was so successful that it quickly replaced the previous generation of bikes.

The basic components of most modern bicycles include a seat, pedals, gearing, wheels and brakes all mounted on a frame. The cyclist pushes the pedals to make the cranks turn, which in turn powers a chain that turns the back wheel of the bicycle to make it move forward. The front wheel is connected to the handlebar, so turning the handlebar swivels the front wheel that steers the bicycle.

Some modern bicycles have a seat tube that extends down from the bottom bracket to provide a place for the rider to sit. This type of bicycle is called a “drop bar.”

A few modern bicycles have hydraulic transmission systems, but the vast majority use a chain and derailleur to transfer power from the pedals to the rear wheel. Some use a shaft drive, and a few use a belt.

Most modern bicycles have pneumatic tires that are filled with air to cushion the ride and give traction over many types of surfaces. These tires require regular maintenance, including airing up and mending punctures, to maintain proper tire pressure and prevent flats. Some bicycles have puncture-resistant tires that incorporate one or more layers of Kevlar to prevent the penetration of sharp objects such as nails, tacks and glass shards.

The manufacture of bicycles has played a critical role in the development of metalworking techniques, especially those for making welded steel frames and components such as lugs. This early industrialization enabled skilled craftsmen to produce high-quality, durable bicycles. In recent years, however, lightweight aluminum alloys have largely replaced steel in the manufacture of bicycle components. In particular, aluminum welding technologies have gotten better, allowing for the production of frames and parts that are both stiff and light. This trend is expected to continue as manufacturing technology evolves. Some modern bicycles are even made of carbon fiber, which is very strong and weighs less than steel.