Three Wheeled Motorcycles : A Question of Science

To stay upright single-track vehicles like motorcycles depend on the gyroscopic effects of wheels in motion and constant corrective steering inputs which together result in an elegant balancing of forces. But once the wheels stop turning, if you don’t put a leg out, you will fall.

There is however, another solution.

One of the most unusual threads to emerge over the past decade of motorcycle design has been the return of the three-wheeler. A strange and unnatural looking vehicle at first glance, the three-wheeled motorized cycle has been with us almost from the beginning. The first car, Karl Benz’ Patent Motorwagen, was a three-wheeler. Bicycles in 1880’s Paris were fitted with two rear wheels to make them practical delivery vehicles for postal and grocery delivery. Motorcycles evolved from bicycles, starting about the same time, so people experimented with tricycle layouts right away.

Over the past century, the motorized tricycle has seen some modest success, largely as a low-speed, light commercial transport. Notable in the genus’ family history is the 1966 Ariel 3, a scooter fitted with two rear wheels that hinged with the rest of the chassis, allowing the scooter to lean in corners like a regular bike while the rear wheels remained horizontal. The Ariel 3 was a failure but Honda bought a licence for the patented layout, beginning a leaning three wheel dynasty that continues to this day with the Honda Gyro, Japan’s takeout delivery vehicle of choice.

Throughout most of the 20th century, three-wheeled motorcycles remained a curio, typically nothing more than home-brewed or limited-production aftermarket conversion kits for conventional motorcycles by small companies, often using car parts on the rear end. In the late 1970’s, the All Terrain Cycle (ATC) hit the dirt with the promise of making the exploding motocross market safe for kids and grandpa, only to end with nearly 1,000 deaths , and the voluntary ban on ATC production by the major manufacturers.

The scandal of the ATC hinged on one inconvenient fact: three-wheeled vehicles are inherently unstable in parabolic (turning) motion. While the unassisted single-track motorcycle flops on its ear at a standstill, the laws of physics turn decidedly in their favour once they roll along, transforming the motorcycle into a paragon of predictable handling at virtually any speed. By contrast, vehicles with three points of contact are balanced at rest and low-speed, but become prone to tipping when loads change suddenly, such as high-speed cornering, especially downhill.

A three-wheeler in parabolic motion produces an undesirable combination of high torque forces on both the roll and yaw axis that are only too happy to overcome gravity and toss you into a ditch. Sidecar riders know this, which is why they have to adopt counterbalancing body postures when cornering to prevent a roll over, particularly on inclines. Even still, it takes little force for the inside wheel to “unstick”, or lose contact with the ground, which causes the center of the vehicles’ roll axis to move further to the outside of the turn, overloading the remaining two wheels.

Reverse trikes such as the Can-Am Spyder and Polaris Slingshot have some significant handling advantages over their ATC predecessors. Because they have two wheels up front, they generate substantially more grip when it is needed most, such as during changes in direction and under braking.

However, the sole rear wheel travels along the centre of the roll axis, and so can act as a pivot point during high energy turns, levering the inside wheel off the ground and flipping the vehicle . This is all mathematically predictable, so can be engineered out by using sophisticated electronic counter-measures without which high-powered, high center of gravity three-wheeler is incapable of executing predictable, safe, high-speed turns without flipping. It is a reality of the laws of physics.

Single-track vehicles enjoy an elegant relationship with the laws of physics that allow them to be used safely by anyone in a wide range of conditions, which is how children can pilot an old bicycle around a corner with little training.

Presented in 2007, Canada’s Bombardier Recreational Products (BRP) launched the Can-Am Spyder forward tricycle. It looked a lot like the snowmobiles that the company was famous for it did not lean when cornering. The rider sits astride the Spyder and operates handlebars as on a motorcycle, but all of the wheels are always perpendicular to the ground.

In 2015 Honda threw its hat in the ring with the Neowing concept, a leaning three wheeler powered by a hybrid system including an inline four cylinder gasoline engine and a battery powered electric motor. Yamaha upped the game with the Niken, a leaning three wheeler billed as a “corning master”.

With these products it seems highly likely that the world’s largest motorcycle manufacturers will pursue this market. It makes sense, and suggests that the holy grail of motorcycling sensation and added safety have been discovered.

According to BRP, the company has sold over 100,000 Spyders. “We are pleased with the platform as it is” said Can-Am’s Brian Manning, when asked if new entrants from Honda and Yamaha might inspire BRP to try to lean in. “Those are different products.”

Motorcyclists looking for the leaning sensation, but with a little more assurance, are not being tempted by the scooter derived MP3 and its imitators. Perhaps the bigger, bolder and more performance oriented Niken will attract them.

Evidence suggests that, for now at least, leaning is not what the marketplace is asking for.