- #1

- 8,873

- 633

In the Wikipedia article on counter-steering, it mentions a roll moment (torque) induced by precession:

https://en.wikipedia.org/wiki/Countersteering#Gyroscopic_effects

It states "The magnitude of this moment is proportional to the moment of inertia of the front wheel, its spin rate (forward motion), the rate that the rider turns the front wheel by applying a torque to the handlebars, and the cosine of the angle between the steering axis and the vertical." The Wikipedia article includes an example that calculates the precession related roll torque being about 12% of the total roll torque, most of which is due to lateral forces between pavement and contact patch. I don't understand how this is quantified, since it would seem that angular inertia about the roll axis would also be a factor, such as a 200 lb motorcycle versus a 400 lb motorcycle.

A classic example of gyroscopic precession is a gyro supported at one end of its axis, with gravity exerting a downwards roll torque, the gyro precessing about a vertical yaw axis, with an upwards counter-torque opposing gravity's downward torque so that the gyro remains horizontal (or nearly so) while precessing. The only torque exerted onto the gyro is the roll torque.

However, in addition to the downwards roll torque from gravity, say there is a yaw torque also applied that prevents precession. How much yaw torque would it take to stop the precession, and what would the reaction be? It would seem that if precession is prevented, then the gyro would simply drop due to the downwards roll torque from gravity, as if the gyro was not spinning, since the gyro's counter-torque to keep it horizontal is due to it's precession, and if the precession is prevented, there is no counter-torque.

https://en.wikipedia.org/wiki/Countersteering#Gyroscopic_effects

It states "The magnitude of this moment is proportional to the moment of inertia of the front wheel, its spin rate (forward motion), the rate that the rider turns the front wheel by applying a torque to the handlebars, and the cosine of the angle between the steering axis and the vertical." The Wikipedia article includes an example that calculates the precession related roll torque being about 12% of the total roll torque, most of which is due to lateral forces between pavement and contact patch. I don't understand how this is quantified, since it would seem that angular inertia about the roll axis would also be a factor, such as a 200 lb motorcycle versus a 400 lb motorcycle.

A classic example of gyroscopic precession is a gyro supported at one end of its axis, with gravity exerting a downwards roll torque, the gyro precessing about a vertical yaw axis, with an upwards counter-torque opposing gravity's downward torque so that the gyro remains horizontal (or nearly so) while precessing. The only torque exerted onto the gyro is the roll torque.

However, in addition to the downwards roll torque from gravity, say there is a yaw torque also applied that prevents precession. How much yaw torque would it take to stop the precession, and what would the reaction be? It would seem that if precession is prevented, then the gyro would simply drop due to the downwards roll torque from gravity, as if the gyro was not spinning, since the gyro's counter-torque to keep it horizontal is due to it's precession, and if the precession is prevented, there is no counter-torque.

Last edited: