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A three wheeled car is an automobile typically having one wheel in the front for steering and two at the rear for power. This reduces the cost of the steering mechanism but greatly increases instability when braking. However, a breed of vehicles having two wheels in the front and one wheel at the back has cult-like following among automotive designers and enthusiasts. One advantage of this configuration is improved aerodynamics, and another is that it readily enables small lightweight motorcycle powerplants and rear wheels to be used. This approach was used by the BMW Isetta and the Berkeley cars T60
For the lowest wind resistance (and best fuel efficiency) a rain drop shape is desired. The surface tension of the water in the rain drop as the air moves past it (or the drop moving through still air) naturally creates this low resistance shape. As the drop begins to fall, the force of the air pushes and distorts the drop. If the force is less in any place, the drop expands in that area. If the force is high in one spot, that spot is pushed in.
A rain drop is wide and round at the front, tapering to a point at the back. The three wheel configuration allows the two front wheels to create the wide round surface of the vehicle. The single rear wheel allows the vehicle to taper at the back.
The disadvantage of a non-tilting three wheel configuration is instability - the car will tip over in a turn before it will slide, unless the centre of mass is much closer to the ground or the wheelbase is much wider than a similar four wheel vehicle. To improve stability some three wheelers are designed as tilting three wheelers so that they lean while cornering like a motorcyclist would do. The tilt may be controlled manually or by computer.
In at least some U.S. states, three wheeled cars are regulated as motorcycles with similar licensing requirements.
See also
- Tricycle (Motorized tricycles)
- Automobile (Replica of the Benz Patent Motorwagen built in 1886)
- Steam tricycle
- Three wheeler