Tilting three-wheeler

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. 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 driven. In addition, there are a variety of feasible choices for which wheels tilt and which do not.
Because this is an emerging field with many different vehicle configurations, many different individual contributors, and not yet any clearly dominant technology, there is a great deal of potentially confusing terminology in use:
The potential benefits of tilting, compared to the rigid alternative, include:
The drawbacks of tilting, compared to the rigid alternative, include:
As with tricycles in general, the two main wheel layouts are:
Twinned Wheel Rule: In many countries aligned to EU regulations, an arrangement of two wheels on the same axle [not necessarily maintained co-axial], is treated as one wheel provided they are spaced no further apart than 460 mm (18 in) 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.
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.
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:
Less common drive configurations include:
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.
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 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.
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:
In the case where the two side-by-side wheels tilt, some mechanical linkage is necessary to coordinate their tilting. Implementations include:
Due to the tilting, there is not necessarily any side-to-side load transfer between the wheels in cornering, so the rule of thumb 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.
In all cases, the tilting mechanism may simply be lockable to facilitate keeping the vehicle upright when stopped or parked. 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.
Enclosures can protect rider(s) from the weather and allow for reduced aerodynamic drag.
Steering requires that the axle(s) of the front wheel(s) form a finite angle with the axle(s) of the rear wheel(s), i.e. not be parallel. This misalignment may be accomplished in a variety of ways, and usually the front wheel(s) rotate about a steering axis relative to the rest of the vehicle and the rear wheel(s). One notable exception, already mentioned above, is the rear-wheel-steered Toyota i-Road.
Some Tilting trikes are forced-tilted, such as the Carver, where the countersteering is not controlled by the operator. Some versions of the model 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.
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.
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 10 mph (16 km/h) 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 10 mph (16 km/h) to improve slow-speed performance where the steerable wheel(s) are progressively captured to the vehicle tilt action as vehicle speed decreases.