A bicycle (also called a bike, pedal cycle, or push-bike) is a human-powered, two-wheeled land vehicle that is powered by a rider sitting on it and pushing the pedals with their feet. It is the most efficient means yet devised for converting human energy into motion. Bicycles are used by millions of people around the world for transportation, recreation, exercise, and competition. The name comes from the prefix “bi-” meaning two, and the suffix “cycle” which refers to the wheels. It has a frame, two pedals, and a chain that connects the cranks to the front and rear wheels. It also has a set of handlebars that the rider grips with their hands.

The first bicycles were made of wood or steel wire, with the cranks attached directly to the front wheel. It was difficult to pedal and steer at the same time, because the rotational planes of the leg and the crank were not aligned. Later, a French mechanic named Pierre Lallement improved the velocipede de pedale by attaching the cranks to the non-steering rear wheel. This allowed the rider to push down on the pedals while turning the front wheel, and it also allowed for gearing to efficiently use the riders power.

Early bicycles were wildly popular, and many manufacturers began producing them in huge quantities. This led to a price war and oversupply, which drove sales down and caused many of the bicycle companies to go bankrupt. The surviving bicycle makers then focused on quality and design innovations to increase sales.

Today, bikes are made from carbon fiber, aluminum, titanium and steel, with each material having its own unique properties. The choice of material impacts the cost, weight, comfort and general “feel” of a bike.

Bike frames come in a variety of sizes and shapes to fit riders of all different sizes and styles. Besides frame size, other factors such as wheelbase and seat angle determine how the bike rides. Using these parameters, engineers and designers can tune a bike to achieve its intended purpose.

The most common bicycles are used for transport and recreation, but some are specialized for racing or other types of sports. Racing bikes are designed to be fast and light, while recreational bikes focus on comfort and durability. Some are equipped with special features such as suspension to absorb shock and allow the rider to sit in a more comfortable position. In addition, some are fitted with accessories such as baskets and carriers to transport items. Other accessories can be added to improve the performance of a bike, such as lights and reflectors, mirrors, and racks. There are even bikes with a built-in computer that can track the speed and distance of a ride. This information can be uploaded to a computer or smartphone for analysis and comparison with other cyclists in a race or on a training ride. This can help the rider to analyze their strengths and weaknesses and identify areas for improvement.