A bicycle is a human-powered, two-wheeled vehicle that can be used for transportation, recreation, or sport. More than 2 billion bicycles are currently in use worldwide, outselling automobiles by a factor of three to one. Bicycles are the most efficient means of human-powered travel, converting about 99% of the energy applied to the pedals into forward motion.

The bicycle is also an excellent fitness machine, providing a low-impact and full-body workout. A 30 minute bike ride burns over 100 calories and builds leg strength, while increasing cardiovascular endurance and aerobic capacity. Unlike some other sports, cycling can be easily adapted to any age or physical condition and can be performed at as low or as high intensity as desired.

Bicycles are generally made of steel or aluminum alloy for strength and light weight, with carbon fiber being used in higher-end models. Frames are often painted or powder coated to protect the finish. There are many accessories available for bicycles, including racks, fenders, lights, mirrors, reflectors, bottle cages, baskets, and bags. In some places, laws require bicycles to be equipped with certain safety devices.

A wide range of tires are available for bicycles, enabling them to be used on many different types of roads and terrain. Some bicycles have disk brakes, which provide more stopping power than rim brakes. Some bicycles have front and rear derailleurs, which allow the rider to shift gears without removing their hands from the handlebars. In addition to standard tires, there are specialized tires for off-road and racing use.

Many cities have bike lanes or paths that separate cyclists from motor vehicles. Increasingly, people are using bicycles for transport to work or school. In urban areas, bikes outnumber cars by more than two to one. Bicycles are also widely used for recreation, as they can be enjoyed in many types of weather and at any time of the day or night.

The invention of the bicycle revolutionized human mobility. It changed the way that people live, work and play, especially in developing countries. Today, the bicycle is the primary mode of transport for millions of people around the world. Its efficiency and convenience make it a popular form of transportation. The bicycle also has a significant environmental impact, reducing air pollution and traffic congestion in cities.

Cycling is a fun and healthy activity for people of all ages and abilities. In the United States, more than 60 million people ride a bicycle regularly. Most are primarily recreational riders, although there are also significant numbers of commuters and athletes.

When riding a bike on the road, be aware of your surroundings and follow all the rules of the road. Yield to other vehicles and pedestrians, and always check behind you before turning. Always wear a helmet, brightly colored clothing or reflective gear, and a reflector on your bicycle at night or in poor visibility. Also, make sure your bicycle fits you and is in good working order before riding it.