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ImageA tricycle (often abbreviated to trike) is a three-wheeled vehicle. While tricycles are often associated with the small three-wheeled vehicles used by pre-school age children, they are also used by adults for a variety of purposes. In the United States and Canada, adult-sized tricycles are used primarily by older persons for recreation, shopping, and exercise. In Asia and Africa, tricycles are used primarily for commercial transportation, either of passengers in pedicabs, or of freight and deliveries.

Human-powered trikes are usually powered by pedals, although some models have hand cranks. Motorized trikes can be powered with a variety of methods, including motorcycle engines, smaller automatic transmission scooter motors, and electric motors. The term "tricycle" may or may not include motorized Three Wheeled Cars, depending on local laws.

ImageTricycles generally follow one of three layouts:

  • Upright, Resembling a two wheeler (diamond frame (traditionally) or open) but with two wheels at the back and the rider straddling the frame. Steering is through a handlebar directly connected to the front wheel like a bicycle;
  • Delta, is similar to an upright, with two wheels at the back and one at the front, but has a recumbent layout in which the rider is seated in a chair-like seat. One or both rear wheels can be driven, while the front is used for steering (the usual layout). Steering is either through a linkage, with the handlebars under the seat (USS) or directly to the front wheel with a large handlebar (OSS); and
  • Tadpole (or reverse trike), a recumbent design with two steered wheels at the front and one driven wheel at the back (though one model has the front wheels driven while the rear wheel steers). Steering is either through a single handlebar linked with tie rods to the front wheels' stub axle assemblies (Indirect) or with two handlebars (rather, two half-handlebars) each bolted to a steerer tube, usually through a bicycle-type headset and connected to a stub axle assembly (Direct). A single tie rod connects the left and right axle assemblies.

ImageThe tadpole trike, which is rapidly becoming the most popular design, is often used by middle-aged or retiree-age former bicyclists who are tired of the associated pains from normal upright bikes ("wedgies" or "DFs" [diamond frames], as they are called in many recumbent forums). With its extremely low center of gravity, aerodynamic layout and light weight (for trikes), tadpoles are considered the highest performance trikes.

Not all trikes fall into one of these three classes. For example, some early pedal tricycles from the late 1800s used two wheels in tandem on one side and a larger driving wheel on the other. Another design is an in line three wheeled vehicle, with two steered wheels: one at the front and the other in the middle or at the rear. It is not unusual for tricycles to have front and rear wheels of different sizes.