A bicycle is a two-wheeled human-powered land vehicle with pedals and a handlebar. A bicycle can be used for recreation, transportation, exercise, or as a means of transporting goods. In the latter case, the bicycle may be fitted with a trailer or a box for cargo. It is also a popular mode of sports and competition, such as racing or artistic cycling. It is the most efficient human-powered means of travel, in terms of the amount of energy a person expends compared to the distance traveled.

Bicycles have a number of safety issues to consider, particularly when sharing the road with motor vehicles. Many thousands of people are injured and killed each year in bicycle accidents. To reduce the risks, bikers should always wear helmets and other protective equipment. Riders should also be aware of their surroundings and follow all traffic rules. They should stay close to the right side of the road in countries where cars drive on that side, and should ride on the left if they are going to pass other vehicles.

There are various types of bicycles, ranging from small children’s models to high-end racers. The main differences between them are the size and type of wheels, the frame, and the suspension system. The most important characteristic of a bicycle is its ability to be maneuvered and controlled. To achieve this, it is necessary to know the geometry of the bicycle and how to adjust its components.

The frame is the central component of a bicycle, giving it its shape and providing strength. The frame is usually made from steel, although aluminum and titanium are sometimes used. It is formed by a truss, with the front triangle consisting of a head tube and a top tube joined together by a down tube, and the rear triangle consisting of a seat tube paired with chain stays. The frame includes a chainstay guard to prevent the rider’s feet from being caught by the wheel, and a chainguard or guard that protects the chain from damage.

Handlebars are the handles that connect to the steering stem, which in turn connects to the fork. There are three common styles of handlebars: upright handlebars, which curve gently back toward the rider for a comfortable position; drop handlebars, which offer the best braking and handling from a crouched or sat up position; and riser handlebars, which are designed to be used in either a dropped or an upright position.

Bicycle tires are normally inflated to a pressure that is higher than that of car tires, typically 60 to 100 pounds per square inch (210 to 690 kPa). This high pressure increases the friction between the tire and the road, which helps to propel the bike. However, the rider should maintain a safe pressure to avoid punctures. If a puncture does occur, the rider should stop riding and seek emergency assistance from a local police department or bicycle shop. The handlebars can be equipped with a variety of accessories to enhance the riding experience, such as clip-on pedals for aerodynamic advantage or to allow the rider to perform tricks, or to carry extra gear.