A bicycle is a human-powered, two-wheeled machine for transporting a rider over long distances. It is considered to be the most efficient means of human transportation in terms of the amount of energy it takes to propel a person over a given distance. It is also considered a very safe form of transportation when used correctly. Despite its relatively simple mechanical construction, the bicycle requires regular maintenance and the replacement of worn parts to keep it operating efficiently and safely. A variety of components and mechanisms allow the bicycle to be adapted for different purposes, such as racing or touring.

Bicycles are typically made of aluminum, steel or carbon fiber. The choice of material depends on the desired weight, stiffness and cost. Aluminum is lightweight and relatively stiff, while steel offers more durability. Carbon fiber is the lightest and most expensive of these materials, but it is also the most durable and has the best shock absorption.

The bicycle was first patented in 1817 by Baron Karl von Drais. His design had a wheel with cranks attached to the frame, but no pedals. A later version added pedals and a chain, making it possible to both steer and power the bicycle. By the early 20th century, bicycles had become widely popular in many nations, reducing crowding in urban tenements and allowing people to commute into suburban areas where they could live more comfortably. They also provided a fast and convenient way to travel for leisure, and were three times as energy efficient as walking or riding horses.

In addition to the forces of friction that slow a bicycle, there are several other dynamic forces at work on a cyclist’s bike. These horizontal forces are generated by the rider’s legs as they push on the pedals, and they are balanced through the cranks, chain, and rear wheel to generate a pushing force that accelerates the bicycle.

Every time a spoke is rotated, it gets pulled on by the rim of the wheel, and that pulling causes the nipple to move down onto the hub. The nipple then pulls on the spoke, trying to screw it into itself, and it is that pulling that creates the tensile load that keeps the wheel centered on itself.

In order to maintain the vertical balance of a bicycle, a rider can simply lean into a turn. This shifts the center of gravity to one side, and the leaning wheel generates a force that counters the horizontal force of friction on the ground. The result is that the bicycle is able to stay upright without any assistance from the hands of the rider. This method of balancing the bicycle is also known as “hands-free stability”. This technique allows people to ride a bicycle with very little effort while maintaining a comfortable posture, and it is an extremely effective means of control for both racing and casual riding. It is also very important to maintain a steady pace while riding on steep hills or in windy conditions.