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A three-wheeler is a vehicle with three wheels. Some are motorized tricycles, which may be legally classed as either automobiles or motorcycles, while others are tricycles without a motor, some of which are human powered vehicles and animal powered vehicles.
Contents
Overview
Many three-wheelers which exist in the form of motorcycle-based machines are often called trikes and often have the front single wheel and mechanics similar to that of a motorcycle and the rear axle similar to that of a car. Often such vehicles are owner-constructed using a portion of a rear-engine, rear-drive Volkswagen Beetle in combination with a motorcycle front end. Other trikes include ATVs that are specially constructed for off road use.
Three-wheeled automobiles can have either one wheel at the back and two at the front, (for example: Morgan Motor Company) or one wheel at the front and two at the back (such as the Reliant Robin). Due to better safety when braking, an increasingly popular form is the front-steering "tadpole" or "reverse trike" sometimes with front drive but usually with rear drive. A variant on the 'one at the front' layout was the Scott Sociable, which resembled a four-wheeler with a front wheel missing.
Three-wheeler cars, including some cyclecars, bubble cars and microcars, are built for economic reasons: in the UK for tax advantages, or in the US to take advantage of lower safety regulations, being classed as motorcycles. As a result of their light construction and potential better streamlining, three-wheeled cars are usually less expensive to operate.
Three-wheeler transport vehicles known as auto rickshaws are a common means of public transportation in many countries in the world, and are an essential form of urban transport in many developing countries such as India and the Philippines.
Auto rickshaws are a form of novelty transport in many Eastern countries.
History
Early automotive pioneer Karl Benz developed a number of three-wheeled models. One of these, the Benz Patent Motorwagen, is regarded as the first purpose-built automobile. It was made in 1885.
In 1896, John Henry Knight showed a tri-car at The Great Exhibition.
In 1897, Edward Butler (inventor) made the Butler Petrol Cycle, another three-wheeled car.
A Conti 6 hp Tri-car competed in (but did not complete) a 1907 Peking-to-Paris race sponsored by a French newspaper, Le Matin.
Two front
A configuration of two wheels in the front and one wheel at the back presents two advantages: it has improved aerodynamics, and that it readily enables small lightweight motorcycle powerplant and rear wheel to be used. This approach was used by the Messerschmitt KR200 and BMW Isetta. Alternatively, a more conventional front-engine, front wheel drive layout as is common in four-wheeled cars can be used, with subsequent advantages for transversal stability (the center of gravity is further to the front) and traction (two driven wheels instead of one).
With two wheels in the front (the "tadpole" form or "reverse trike") the vehicle is far more stable in braking turns, but remains more prone to overturning in normal turns compared to an equivalent four-wheeled vehicle, unless the center of mass is lower and/or further forward. Motorcycle-derived designs suffer from most of the weight being towards the rear of the vehicle.
For lower wind resistance (which increases fuel efficiency), a teardrop shape is often used. A teardrop is wide and round at the front, tapering 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. Examples include the Aptera 2 Series and Myers Motors NmG.
Two rear
Having one wheel in front and two in the rear for power reduces the cost of the steering mechanism, but greatly decreases lateral stability when cornering while braking.
When the single wheel is in the front (the "delta" form, as in a child's pedal tricycle), the vehicle is inherently unstable in a braking turn, as the combined tipping forces at the center of gravity from turning and braking can rapidly extend beyond the triangle formed by the contact patches of the wheels. This type, if not tipped, also has a greater tendency to spin out ("swap ends") when handled roughly.
Lateral stability
The disadvantage of a three-wheel configuration is lateral instability - the car will tip over in a turn before it will slide. This can be prevented in 3 ways:
In the case of a three wheeled ATV, tipping can be avoided by the rider leaning into turns.
Tilting option
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, mechanically or by computer.
A tilting three-wheeler's body and or wheels tilt in the direction of the turn. Such vehicles can corner safely even with a narrow track.
Some tilting three-wheelers could be considered to be forms of feet forwards motorcycles, or cabin motorcycles, or both.
Wheel configurations
Several configurations are practical. Two front wheels and one rear, where all three wheels tilt, use the acronym 2F3T (i.e. two front three tilt). Other variations 1F1T, where only the front wheel tilts, an example being the Vandenbrink Carver, made in the Netherlands.
Active or passive tilt control
Tilting can be actively controlled by applying force between the paired wheels. A "free leaner" is balanced by steering, like a single track vehicle. This still leaves some advantages in traction, and the tilt can be locked for parking faster than a stand can be deployed.
Topology
Propulsion may be on one, two, or three wheels, tilted or not. Many possible arrangements require particularly flexible U-joints, which favours the other possibilities.
Use of 'extra' wheel
Any extra laterally spaced wheel can benefit the vehicle by providing stability gains if there is a mechanism to lock the laterally spaced wheels at any given moment relative to the road plane. In some countersteered vehicles this benefit is generally only available when stopped.
In other types where the tilt angle is directly controlled this additional stability is constant at all speeds.
In a countersteered vehicle a loss of traction will result in a fall whereas in a tilt controlled design a fall may not occur.
Various electric and hydraulic systems have been employed to modify TTW behaviour, with notable success on the Carver.
Due to the tilting, there is not necessarily any load transfer between the wheels in cornering, so the rule about tadpoles (2F or "reverse trike") understeering and Deltas (1F or standard trike) oversteering does not necessarily apply.
Battery
Three-wheeled battery powered designs include:
Solar
The world's fastest solar-powered vehicle, Ashiya University's Sky Ace TIGA, is a three-wheeler. It achieved 91.332 kilometres per hour (56.751 mph) at Shimojishima Airport, in Miyakojima, Okinawa, Japan, to win the Guinness World Record, on 20 August 2014. It took the record from another three-wheeler, Sunswift IV, designed and built at the University of New South Wales in Australia, by a margin of almost 3 km/h.
Steam
The world's first full-size self-propelled land vehicle was a three-wheeler. French Army Captain Nicolas-Joseph Cugnot's 1770 fardier à vapeur (steam dray), a steam tricycle with a top speed of around 3 km/h (2 mph), was intended for hauling artillery.
Another of the earliest preserved examples is the Long steam tricycle, built by George A. Long around 1880 and patented in 1883, now on display at the Smithsonian Institution.
All-terrain vehicles
Due to the incidence of injuries related to their use, a 10-year ban, entirely voluntary for manufacturers, was placed on the sale of new three-wheeled all-terrain vehicles in the United States in January 1988. However, it should be noted that more injuries were sustained by riders by not applying a proper riding technique, and lack of wearing proper safety gear such as helmets and riding boots. In a search conducted by the Consumer Product Safety Commission, it was determined that "no inherent flaw was found in the three wheel design".
Registration
In the U.S, the National Highway Traffic Safety Administration defines and regulates three-wheeled vehicles as motorcycles.
Driver's license requirements vary on a state-by-state basis. In other jurisdictions, such as British Columbia, Canada, and Connecticut, a three-wheeled vehicle with an enclosed passenger compartment or partially enclosed seat is considered an automobile.