Strictly speaking, bicycles can only have two wheels, since the term "bi" means "two." However, since tricycles or trikes are commonly associated with young children, many companies use the term three-wheel bicycle to refer to tricycles for adults. Adult-sized three-wheel bicycles use a variety of wheel and seat configurations, as well as optional features for transporting goods or passengers. Adults may use three-wheel bicycles for recreational, competitive and industrial purposes.
Types
Most three-wheel bicycles are either of an upright style, similar to most two-wheel bicycles, or a recumbent style, which allows the user to recline while still reaching the extended handlebars. Both of these styles generally have one wheel in the front and two wheels in the back. In contrast, tadpole-style three-wheel bicycles and some industrial tricycles have two wheels in the front and one wheel in the back. Tri-tandems have two seats (one behind the other), while dual trikes allow two riders to sit side by side, each with his own set of pedals.
Features
All three-wheel bicycles have features similar to those of regular bicycles, such as a seat, wheels, frame and foot- or hand-operated brakes. Many adult three-wheel bicycles also feature a basket on the front or rear of the bike. Some industrial three-wheel bicycles have a platform built into the front or back for carrying large objects, such as boxes or suitcases, and some have an enclosed compartment for transporting cargo, hot foods or ice cream. Other three-wheel bicycles have a seat with a set of pedals in the front, and a seat for one or more passengers in the back.
Function
Riders use three-wheel bicycles for recreation, as well as for racing or for work. Since three-wheel bicycles are heavier than two-wheel bicycles, riders who wish to race often use specialized tricycles that are built to be aerodynamic and lightweight. In contrast, industrial or heavy-duty three-wheel bicycles work well for street vendors, who use the cargo compartment as a portable restaurant or merchandise display stand, as well as for rickshaw drivers, who transport people in the passenger seat of a three-wheel bicycle, much like a taxi service. Some three-wheel bicycles also feature umbrellas or sunshades.
Benefits
Three-wheel bicycles have better stability than two-wheel bicycles, and can support a heavier or wider load. Many riders who are unable to use a traditional narrow bicycle seat--including elderly riders or those with disabilities--are more comfortable in an upright or reclined three-wheel bicycle seat, since these seats are often significantly wider and more padded. Recumbent or delta-style three-wheel bicycles, as well as some upright models, also have a padded seat back for better comfort and support. Like other types of bicycles, three-wheel bicycles require no fuel for transportation, and provide riders with exercise.
History
The first bicycle to use a mechanical crank--rather than being pushed along by feet against the ground--appeared in the 1860s. One of the most common original models, the penny-farthing, had a very large front wheel and a small back wheel, making it difficult to ride and balance. To solve this problem, some bicycles began incorporating an additional back wheel for stability, making them into tricycles. By the 1870s, wooden tricycles had become enormously popular for children, and in the 1880s, three-wheel bicycles that allowed two riders to sit side by side became popular with adults. Three-wheel cycle rickshaws, or pedicabs, first appeared in the United States in 1962, and have become widely popular in Southeast Asia, as well as in London, Rome and other major European cities.
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