A tilting three-wheeler, or tilting trike is a three-wheeled vehicle whose body and or wheels tilt in the direction of a turn, and is usually a narrow-track vehicle. 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. This also reduces the lateral acceleration experienced by the rider, which some find more comfortable than the alternative. The narrow profile can result in reduced aerodynamic drag and increased fuel efficiency. These types of vehicles have also been described as "man-wide vehicles" (MWV).
As with tricycles that do not tilt, there are a variety of feasible choices of how the wheels are arranged, which wheels are steered, and which wheels are drive. In addition, there are a variety of feasible choices for which wheels tilt and which do not.
Benefits and drawbacks
The benefits of tilting, compared to the rigid alternative, include:
- The ability to balance the moment caused 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 long 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:
- Any kind of tilting mechanism, whether free or controlled, invariably requires more complexity and either more weight and/or more cost.
- Control of the tilting either requires some kind of automated control system or different behavior from the rider, such as countersteering.
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.
Rear-wheel steering tends to be directionally unstable, and so the vast majority of trikes employ front-wheel steering. 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.
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.
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.
Any number of the wheels can tilt, and advantages to tilting wheels are that the wheels do not need to bear large side loads, and the tires mounted on them can generate camber thrust, which can reduce the need for a slip angle to generate cornering force. 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.
- 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. This tends to be employed on delta trike configurations.
Due to the tilting, there is not necessarily any side-to-side load transfer between the wheels in cornering, so the rule about tadpoles understeering and deltas oversteering does not necessarily apply. 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.
Active or passive tilt control
Tilting may be either passive, as with a bicycle or motorcycle, in which case countersteering is required, or active, where the rider or some other controller actively sets the lean angle directly. Vehicles for which the rider has direct control over the lean angle include the General Motors Lean Machine, in which the rider controlled lean with foot pedals, and the Tripendo, in which the rider controls lean by hand with a lever. An active controller may calculate a desired lean angle from some combination of lateral acceleration and steering input, and it may set a desired lean angle with some combination of mechanical, electrical, or hydraulic actuators. In any case, active tilting systems cannot simply counter the roll moment caused by gravity, as this has been shown to make a vehicle unsteerable.
- Unenclosed vehicles may employ passive tilt control because the rider can still put a foot down when stopped. The rider is responsible for controlling tilt just as they would on a two-wheeled bicycle or motorcycle.
- Enclosed vehicles, in which the rider cannot reach the ground, must provide come kind of active tilt control, either automatically or under rider control, to keep the vehicle upright when stopped.
In either case, the tilting mechanism may be lockable to facilitate keeping the vehicle upright when stopped or parked.
Tilting trikes that are forced-tilted, such as the Carver, are tilted without countersteering the control and are not balanced by the operator. Later versions of the Carver introduced automatic countersteer to increase tilt speed and reduce the force required to tilt the vehicle. Other forced-tilted vehicles may incorporate automatic countersteering. A prototype tilting multi-track free leaning vehicle was developed in 1984 that employs automatic countersteering and does not require any balancing skills.
Use of 'extra' wheel
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There is no general agreement on how much, or even what use to make of the third wheel on a tilting trike. Sometimes it does little more than a kickstand with a caster, employed at low speed. These vehicles are called free-leaners and they must be balanced and leaned into a turn with countersteering, just as with motorcycles or other single-track vehicles. Free-leaners can feel more comfortable because the net ground reaction force remains aligned with the midplane of the vehicle and riders to not experience lateral forces, as they do in non-tilting vehicles. Most motorcycles using this technology are scooters. According to the manufacturers' marketing these three-wheelers are more stable, have a better weight distribution and handle poor road surfaces better compared to a standard two-wheeled scooter.
Other tilting trikes use the third wheel to resist wind loads and force a faster lean to set up for a fast corner or emergency lane change. Opinion is divided on how best to control this benefit, and various electric and hydraulic systems have been employed to create specific tilting behaviour, with notable success on the Carver. An alternative is for the driver to control the tilt only, and the chassis steers automatically. This may be easier to learn for drivers.
Ariel 3 from 1970. (1F1T)
MEV Tilting Trike, patented in 2005. (1F1T)
Honda Canopy used for delivery service (1F1T)
CLEVER prototype without bodywork, June 2013. (1F1T)
Rose-Hulman Ragnarök (1F3T)
Toyota i-Road (2F3T)
Yamaha Tricity (2F3T)
Piaggio MP3 (2F3T)
Piaggio MP3 (2F3T) with roof and wagon
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Camber thrust is the ability of a tire to generate force when leaned over during a turn.
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The single front wheel layout naturally oversteers and the single rear wheel layout naturally understeers.CS1 maint: uses authors parameter (link)
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- Tilting Three Wheelers - Patents
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- Carver One
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