The design of the Tricycle

A tricycle (often abbreviated to trike) is a three-wheeled vehicle.

 Design:
Tricycles generally follow one of three layouts:
 1.upright, Resembling a two wheeler (diamond frame) 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;
 2.delta, is similar to an upright, with two wheels at the back and one at the front, but has a recumbent layout. 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
 3.tadpole (or reverse trike), a recumbent design with two steered wheels at the front and one driven wheel at the back. Rarely (because of the problem of tipping over at speed), the front wheels can be driven while the rear wheel steers. Steering is either through a linkage and a tie rod to the plates of the spindle assemblies (USS) or with two handlebars, each connected to a steerer tube (usually through a bicycle headset, with the handlebars acting as stems) and a tie rod between the plates of the spindle assemblies (OSS).
The tadpole trike, which is rapidly becoming the most popular design, is often used by middle-aged 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 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.