Bike

A bicycle, commonly referred to as a bike, is a human-powered, pedal-driven vehicle with two wheels attached to a frame. It typically uses a steering system via handlebars, a saddle for seating, and a drivetrain that drives the rear wheel through a chain. Modern bikes may incorporate gears, suspension, and electric assist.

The basic concept emerged in the 19th century with early designs such as velocipedes and the boneshaker. The modern form, featuring a chain-driven rear wheel, equal-sized wheels, and a diamond-shaped frame, was developed in the 1880s and popularized by John Kemp Starley as the safety bicycle.

Frames are commonly constructed from steel, aluminum, carbon fiber, or titanium. The drivetrain includes pedals, a crankset, a chain, and usually a derailleur to vary gear ratios. Wheels comprise rims, spokes, tires, and hubs. Braking systems include rim brakes and disc brakes, with suspension options on some models.

Bicycles are used for transportation, recreation, sport, and commuting. They offer high energy efficiency and emit no pollution during operation. They can reduce traffic congestion and improve health, while requiring space for storage and maintenance infrastructure such as bike lanes and parking facilities.

Safety and regulations vary by country but commonly emphasize helmet use, lighting, reflectors, and rules of the road. Regular maintenance, such as checking brakes, tires, and gears, is important for safe operation.

Variants include road bikes, mountain bikes, hybrids, touring bikes, gravel bikes, BMX bikes, cargo bikes, and folding bikes. Electric bicycles add a motor assist, expanding range and load-carrying capability.