thumb|[[Vandenbrink Carver (1F1T)]]

thumb|Tripendo recumbent tricycle, a tilting three-wheeler (2F3T)

thumb|[[Yamaha Niken from 2018]]

thumb|[[University of Wisconsin–Milwaukee|UWM PantherTrike, a narrow-track, tilting, recumbent, human-powered trike (1F3T)]]

A tilting three-wheeler, tilting trike, leaning trike, or even just tilter, is a three-wheeled vehicle and usually a narrow-track vehicle whose body and or wheels tilt in the direction of a turn. Such vehicles can corner without rolling over despite having a narrow axle track because they can balance some or all of the roll moment caused by centripetal acceleration with an opposite roll moment caused by gravity, as bicycles and motorcycles do. These types of vehicles have also been described as "man-wide vehicles" (MWV). "Free" and "passive" usually mean that the vehicle tilts as a bicycle or motorcycle, and the rider must control the tilt angle indirectly by steering the vehicle.

  • direct and indirect usually refer to how active control is applied. The rider on a "free-tilting" and "passive-tilting" trike usually can apply a steer torque directly, which then controls the tilt angle indirectly, as on bicycles and motorcycles. The rider on a "free-to-caster" trike, on the other hand, can apply a roll torque directly, which then controls the steer angle indirectly.
  • highside and lowside are expressions already commonly used in the motorcycle world to describe ways in which the bodies of these vehicles may collide with the ground.

Benefits and drawbacks

The potential benefits of tilting, compared to the rigid alternative, include:

  • The ability to balance the moment caused by lateral acceleration in a turn, due to high speed, tight radius, or both, with a counter moment caused by gravity, means these vehicles do not have to be low, wide, and/or slow. Also, since stability no longer depends on the axle track, the center of mass does not have to be located near the wide axle and instead can be located anywhere between the front and rear axle to optimize other performance characteristics such as ride quality or braking performance.
  • Leaning into a turn, as bicycles and motorcycles do, means that the net acceleration experienced by the vehicle and rider can always be aligned with the midplane of the vehicle. Riders may find this more pleasant than the alternative, and vehicle components, such as the frame, wheels, and tires, can avoid large side loads.
  • A narrow axle track means that the vehicle does not require as much pavement and may experience less aerodynamic drag because of a smaller cross-sectional area.
  • Depending on how the tilting is implemented, a tilting vehicle can be oriented independent of cross slope, such as from the crown in a road or a soft shoulder.

The drawbacks of tilting, compared to the rigid alternative, include:

  • The tilting mechanism, free or controlled, requires more constructive elements compared to two-wheeled (motor-) cycles, while independent suspension of rigid three-wheelers may be more complex
  • Control of the tilting either requires some kind of automated control system or different behavior from the rider, such as countersteering.

Configurations

Wheel layout

As with tricycles in general, the two main wheel layouts are:

  • delta, with one wheel in front and two wheels in back. Notable examples include the Ariel 3, MEV Tilting Trike, Honda Canopy, Vandenbrink Carver, and CLEVER.
  • tadpole, with two wheels in front and one wheel in back. Notable examples include the Piaggio MP3, Yamaha Tricity, and Toyota i-Road.

Twinned Wheel Rule: In many countries aligned to EU regulations an arrangement of two wheels on the same axle is treated as one wheel provided they are spaced no further apart than between contact patch centers. This has the effect of allowing vehicles complying with this dimensional limit to be classified as motorcycles. Therefore, such vehicles would be subject to all the technical prescriptions applicable to motorcycles rather than motorised tricycles or four-wheeled vehicles.

Steered wheels

Rear-wheel steering tends to be directionally unstable, and so the vast majority of trikes employ front-wheel steering. A notable exception is the Toyota i-Road. In the case of two wheel steering, some accommodation is usually made to account for the different radii of their paths, such as Ackermann steering geometry.

Driven wheels

Either the front or rear wheel(s) may be driven, but driving a wheel near its power source is usually simpler than driving a wheel at the other end of the vehicle, driving a single wheel is usually simpler than driving a pair of wheels, and driving a wheel that remains aligned with its power source is simpler than driving a wheel that tilts or steers relative to its power source. Two common drive configurations are:

  • Drive two non-tilting wheels in the rear. Notable examples include the Ariel 3, MEV Tilting Trike, Honda Canopy, Vandenbrink Carver, and CLEVER.
  • Drive one tilting wheel in the rear. Notable examples include the Piaggio MP3, Yamaha Tricity, and Toyota i-Road.

Less common drive configurations include:

  • Drive two tilting wheels in the rear.
  • Drive one tilting wheel in the front. One example is the Rose-Hulman Ragnarök pictured below.

Seating

As with tricycles in general, seating may be upright, as on the Piaggio MP3, or recumbent, as on the MEV Tilting Trike. If the vehicle is designed to accommodate a second rider, the seating is usually arranged in tandem to maintain the narrow profile, as on the CLEVER.

Enclosure

The rider may be fully exposed, as on the Tripendo, behind a fairing or windscreen, as on the Piaggio MP3, under a canopy, as on the Honda Canopy, or fully enclosed, as on the Vandenbrink Carver.

Power

Power may come from the rider, as on the Tripendo, from batteries and electric motors, as on the Toyota i-Road, or from conventional internal combustion engines, as on the Yamaha Tricity.

Tilting

Any number of the wheels can tilt, and advantages to tilting wheels are that the wheels do not need to bear large side loads, Configurations include:

  • One wheel in front and only the front tilts, referred to as 1F1T (i.e. one front one tilts). Notable examples include the Ariel 3, MEV Tilting Trike, Honda Canopy, Vandenbrink Carver, and CLEVER.
  • One wheel in front and all three wheels tilt, referred to as 1F3T (i.e. one front three tilt). An example can be seen in the Rose-Hulman Ragnarök pictured below and the UWM PantherTrike pictured above.
  • Two wheels in front and only the single rear wheel tilts, referred to as 2F1T (i.e. two front one tilt).
  • Two wheels in front and all three wheels tilt, referred to as 2F3T (i.e. two front three tilt). Notable examples include the Piaggio MP3, Yamaha Tricity, and Toyota i-Road.

In the case where the two side-by-side wheels tilt, some mechanical linkage is necessary to coordinate their tilting. Implementations include:

  • Some form of one or more parallelograms, such as on the Tripendo pictured above and the Mercedes-Benz F300 Life Jet Concept Vehicle pictured below. This has been employed on tadpole and delta trike configurations.
  • Some form a pair of swingarms, possibly connected by some form of bell crank. This tends to be employed on delta trike configurations.
  • Some form of crank, in which case the two wheels are not directly side-by-side. If the tilting mechanism has some limitation on tilt angle, then the lateral acceleration the vehicle can experience without rolling over will be a function of maximum tilt angle possible, axle track, and center of mass location. Actively controlled tilters are where the rider or some other controller actively sets the tilt angle directly. Vehicles for which the rider has direct control over the tilt angle include the General Motors Lean Machine, in which the rider controlled tilt with foot pedals, and the Tripendo, in which the rider controls tilt by hand with a lever. An active controller may calculate a desired tilt angle from some combination of lateral acceleration and steering input, and it may set a desired tilt angle with some combination of mechanical, electrical, or hydraulic actuators.
  • Free-tilting/passive-tilting vehicles possess no stability about their roll axis when stationary. To remedy this problem some free/passive tilters use tilt locks or restraints when at low speeds. Some use a brake applied to the tilting mechanism, some use progressive roll stability adjustments. Free/passive tilters possess self stability when moving forward with sufficient traction, as with bicycles and motorcycles, and if traction is lost the vehicle will likely lowside. Also, passive or active tilting systems cannot simply counter the roll moment caused by gravity, as this has been shown to make a vehicle practically unsteerable, although there is ongoing debate about whether it is truly unsteerable or not. A prototype tilting multi-track free leaning vehicle was developed in 1984 that employs automatic countersteering and does not require any balancing skills.

A larger range of tilting three-wheelers has appeared in the recent years and use manually controlled countersteering like a motorbike, such as the Piaggio MP3 or Yamaha Niken.

Free to castor

One vehicle variation is to control the steered wheel(s) indirectly by tilting them, along with the vehicle body, and this system is known as free to castor [FTC]. The directional control of a FTC wheel is not particularly strong, as demonstrated by the wheels on a shopping cart, and the castored wheel(s) will turn due to any applied side loading. If the steering axis is not vertical, however, the directional stability above about is very strongly controlled by the dynamic forces. If the castored wheel is attached to the front of a narrow tilting vehicle the castor will automatically place itself on the correct steer angle for the tilt and the speed of the vehicle. A system can be used below to improve slow-speed performance where the steerable wheel(s) are progressively captured to the vehicle tilt action as vehicle speed decreases.

Examples

<gallery>

File:Ariel 3 cropped.JPG|Ariel 3 from 1970. (1F1T)

File:Tilting trike.jpg|MEV Tilting Trike, patented in 2005. (1F1T)

File:Honda Canopy AnnaMillers Tokyo 2004-02-29.jpg|Honda Canopy used for delivery service (1F1T)

File:The CLEVER Vehicle Prototype at the University of Bath.JPG|CLEVER prototype without bodywork, June 2013. (1F1T)

File:Flevotrike.jpg|Flevotrike (1F1T)

File:Rose-Hulman Ragnarök.jpg|Rose-Hulman Ragnarök (1F3T)

File:Tilter_front.jpg|SynergEthic Tilter (1F3T)

File:University of Wisconsin-Milwaukee narrow-track, tilting, recumbent trike.jpg|University of Wisconsin-Milwaukee narrow-track, tilting, recumbent trike (1F3T)

File:I-road - Grenoble.JPG|Toyota i-Road (2F3T)

File:ヤマハ -TRICITY 発表会 (14569130633).jpg|Yamaha Tricity (2F3T)

File:Piaggio mp3.jpg|Piaggio MP3 (2F3T)

File:Piaggio MP3 Roof & Wagon.jpg|Piaggio MP3 (2F3T) with roof and wagon

File:Gilera Fuoco 500cc.jpg|Gilera Fuoco (2F3T)

File:Peugeot Metropolis 400i.JPG|Peugeot Metropolis 400i (2F3T)

File:Quadro350D 1.jpg| (2F3T)

File:1997 Mercedes-Benz F300 Life Jet Concept Vehicle.jpg|Mercedes-Benz F300 Life Jet Concept Vehicle, 1997. (2F3T)

File:Yamaha Niken - Mondial de l'Automobile de Paris 2018 - 004.jpg|2018 Yamaha Niken. (2F3T)

</gallery>

See also

  • Bicycle and motorcycle dynamics
  • Flexible sidecar
  • Tilting train
  • Tilting car

References

Bibliography

  • Poelgeest, A., Edge, K. A. and Darling, J., 2007. Development of a Steer Tilt Controller for a Three Wheeled Tilting Vehicle. In: ASME International Mechanical Engineering Congress and Exposition, 2007-11-01, Seattle, Washington.
  • Tilting Three Wheelers - Patents
  • The Design, Implementation and Analysis of Motorized Tilting Three-Wheelers. Thesis, Choa-Chin Weng. 18 July 2005. Chinese. English abstract.
  • Dynamic Stability of Three-Wheeled Vehicles in Automotive-Type Applications. Robert Q. Riley.
  • Carver One