A bicycle is a pedal-powered two-wheeled vehicle that is often used for transportation. It is a common mode of travel and is an aerobic exercise that can improve physical and mental health. Cycling is a time-efficient form of transport that can replace sedentary (sitting) time spent driving motor vehicles or using trams, trains and buses.

Bicycles can be made from a variety of materials and are a relatively inexpensive form of transportation. However, they can be unsafe for novice cyclists due to the fact that they are vulnerable to road hazards and collisions with other people or objects.

Traditionally, bicycles were designed to be light and strong. This meant that they were largely made from carbon fiber or aluminum alloy. Over the years, these materials have become less expensive and are becoming more commonplace in mid-range bikes.

Many modern bicycles use a diamond frame, a double-triangle truss that consists of a head tube, top tube, down tube and seat tube. The front triangle has a fork and the rear triangle has the seat and chain stays.

The diamond frame is important because it makes the bike more rigid and able to withstand braking. It is also more stable at high speeds, which makes it safer to ride on uneven surfaces.

Although the diamond frame is a very common feature of bicycles, other types of frames can be found as well. These include the track bike and mountain bike.

Historically, steel has been the most common material for frames and components in bicycles. It is a durable metal that has excellent strength and corrosion resistance.

In the 1930s, however, alloy steels became available that were stronger and lighter than steel. This allowed for the development of more affordable and safer bikes.

Another major design improvement was the introduction of multiple-speed gearing. This allowed for larger front wheels and faster speed.

These innovations were developed to overcome the limitations of the velocipede de pedale, the first pedal-powered bicycle. These machines could be very large in size, which prevented them from being easily maneuvered. These designs were not practical for many of the people who wanted to buy them.

Other improvements included a frame-mounted crank, which enabled the pedals to be moved up and down in a way that would reduce the distance to the back wheel. This design eliminated the need to steer the velocipede via the front wheel.

It also reduced the number of components needed to make a bicycle work, as all the moving parts were mounted on the frame instead of the front wheel. It was also more durable, as the cranks were protected from corrosion by the frame.

During the twentieth century, bicycles were further improved by integrating brakes into the frame design and by adding a front fork to reduce the front wheel’s weight. These changes made bicycles more maneuverable, making them more popular among recreational riders.