Tilting System

Camber Thrust

Tilting the wheels of a car so that they lean into a corner (like on a motorcycle) is most beneficial because it creates “camber thrust.” Tires can develop cornering force in two ways: slip angle and camber thrust. Slip angle cornering force is developed by turning the wheel in the desired direction of travel. When the wheel is turned the rubber on the car’s contact patch with the road deforms. This deformed patch of moving rubber creates a lateral force on the tire, causing the car to turn. Camber thrust, on the other hand, is generated when a rounded-profile tire is tilted into the desired direction of travel. The rounded edge of the tire causes the tilted wheel to want to follow an elliptical path, creating lateral force which causing the car to turn.

Because slip angle cornering thrust is developed from the deformation of the tire rubber, it generates a lot of heat. This heat degrades the tire over time. Camber thrust, on the other hand, does not deform the tire as much as slip angle thrust and thus does not create as much tire-degrading heat.

 

Tilting Approach 1: Lean Entire Vehicle with Driver’s Weight

The easiest way to create a tilting vehicle is to soften up the suspension and allow the driver to lean the vehicle by shifting his weight.

This method is used by the following vehicles:

• Piaggio MP3
• Honda Gyro
• Yamaha Tricity
• Peugeot Metropolis
• 4MC Four Wheeled Motorcycle
• Brudeli Leanster
• Tilting Motor Works
• Harley Davidson Penster
• Too Kool Cycles TRT
• TreMoto
• CarvX
• D-Art
• Sway Motorsports Electric Trike

Obviously the downside to this method is that the softer suspension required to allow the driver to lean the vehicle can cause the vehicle to have worse road-holding capability.

 

Tilting Approach 2: Lean Only the Suspension with Power Assist

The third method for tilting a car is to lean the suspension by itself with a power assist while leaving the car un-leaned. A system called the “Sacli Suspension” allows this to happen by creating two separate suspension systems that are linked in series. The “inboard” suspension controls up-and-down motion while the “outboard” suspension controls roll.

The first downside of this method is that it results in a much more complex suspension geometry, making it extremely difficult design and optimize.

The second downside of this method is that the driver doesn’t tilt with the car, so there is no sensation of leaning into the corner. Simply put, it isn’t as fun.

 

Tilting Approach 3: Lean Entire Vehicle with Power Assist

The second method is to tilt the entire vehicle using a power assist like a hydraulic ram or electric linear actuator.

This method is used by the following vehicles:

• Heikki Naulapää’s Aprilia Magnet
• Vandenbrink Carver
• Nissan Land Glider
• Toyota i-Road
• Nathaniel Salzman‘s Project Streetliner

This is the method I plan to use for my car. There is no need to re-invent the wheel (literally) so I’m going to base my design heavily on the cars mentioned above.

Here is a CAD build-up of the Aprilia Magnet showing the suspension geometry – pause it at 11 seconds:

Here is a cardboard model of a similar suspension geometry created by Nathaniel Salzman: