Is Counter-Steering the Only Way to Change Direction on a Motorcycle?

[Erunanethiel]

At high speeds the self correction that steers a bike into the direction of lean goes away and instead the bike tends to hold a lean angle without counter-steering used to change the lean angle. The mathematical models call this "capsize" speed, where the modeled bike falls inwards at very slow rate, so slow that it's imperceptible. The mathematical models may not take into account that the contact patch shifts inwards due to deformation, which would counter the slow inwards falling. The actual effect reported by motorcycle racers is that once leaned, a bike at high speeds tends to hold the lean angle, and the rider has to counter-steer to make any change in lean angle, and that weight shifting has no perceptible effect. The amount of effort to counter-steer increases as speed increases, and at these high speeds, it takes a significant amount of counter-steering effort to change lean angle.

Why does self correction that steers the bike go away at high speeds? Isn't it due to gyroscopic effects from the wheels? Or is it because of the camber thrust?

 

[rcgldr]

Why does self correction that steers the bike go away at high speeds? Isn't it due to gyroscopic effects from the wheels? Or is it because of the camber thrust?

It's due to gyroscopic effects becoming dominant at high speed. At "normal" speeds, the steering geometry results in self corrective steering that tends to return a bike to a vertical orientation, but at high speeds, the tendency is to hold the current lean angle. At "normal" speeds, a small amount of counter-steering is needed to overcome the steering geometry to hold a lean angle, while at high speeds, virtually no rider input is needed to hold a lean angle. At high speeds, a rider has to use counter-steering to make any change in lean angle.

Wiki has a section about the mathematical model. Start at

https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics#Lateral_motion_theory

and skip down to the eigenvalues section. Note the graph which shows a "capsize" speed around 8 m /s. Turns out this was wrong for the bike being modeled as it was noted as being "very stable" at 8.33 m/s (30 kph) on a large treadmill test. The actual "capsize" speed would be higher than what the graph shows. The model uses "knife edge" tires, as opposed to the actual tires used on the bike, so the actual "capsize" speed is higher. The effect is real though. I only had one personal experience with high cornering speeds, and it's true that if you ease off the handlebars, nothing happens. At lower speeds, if I ease off the handlebars, the bike tends to return to a vertical orientation, which is what the steering geometry (trail) is supposed to accomplish. At lower speeds, I have to apply a small amount of counter-steering input in order to hold a lean angle and prevent the bike from returning to vertical orientation. I always counter-steer to control lean angle and never rely on weight shifting, and I didn't experiment with weight shifting at high speeds, but motorcycle racers report that weight shifting is useless at high speeds.

> Camber thrust

There's are conflicts in what camber thrust means. It's basically a relationship between contact patch deformation and the lateral force at the contact patch. This would be one of the differences with a mathematical model based on knife edge tires with no contact patch deformation and the real word. My understanding is the contact patch deformation increases the speed at which "capsize" mode occurs. Wiki article:

https://en.wikipedia.org/wiki/Camber_thrust

 

[Erunanethiel]

Is it possible to create another thread about this? All the people have answered greatly, but the way I asked the original question caused the thread not being able to yield the answer I was looking for.

If there are moderates that can inform me if I can create a new thread asking the same question but in a different and more specific way, please let me know. Thank you very much to all the people who have helped me in this thread and epically to Rcgldr who also helped me via messages.

 

[GeorgeX45]

As a motorcycle rider you might start from the way that you initiate a turn. At low speeds, when the rotational inertia of the wheels is low, you turn the front wheel to the right to turn right. At high speeds, when the rotational inertia of the wheels dominates the behaviour of the motorcycle, you turn the front wheel to the left to turn right. When turning the rider moves on the motorcycle to lower the centre of gravity which it is suggested increases the traction (see the book by John Surtees) although this may have more to do with preventing the motorcycle from flipping outwards by reducing the turning moment about the tyre contact patch - watch what happens when the contact is lost and the motorcycle starts to slide versus being high sided.

 

[rcgldr]

As a motorcycle rider you might start from the way that you initiate a turn. At low speeds, when the rotational inertia of the wheels is low, you turn the front wheel to the right to turn right. At high speeds, when the rotational inertia of the wheels dominates the behaviour of the motorcycle, you turn the front wheel to the left to turn right. When turning the rider moves on the motorcycle to lower the centre of gravity which it is suggested increases the traction (see the book by John Surtees) although this may have more to do with preventing the motorcycle from flipping outwards by reducing the turning moment about the tyre contact patch - watch what happens when the contact is lost and the motorcycle starts to slide versus being high sided.

A bicycle or motorcycle has to be leaned inwards in order to keep from falling outwards during a turn. Regardless of speed, counter-steering to setup the initial leaning motion is always needed. The unicycle guys understand this, since there's no steering reaction to lean as there is with a bike.



Getting back to the bicycle / motorcycle there are three speed ranges that affect how a bike behaves while turning.

There's a moderate speed where the bike is self stable, and the bike's steering geometry tends to return the bike to a vertical orientation if the bike is leaned. At moderate speeds, the rider has to apply a small amount of counter steering to hold a lean angle and prevent the bike from returning to vertical. On many bikes, braking while leaning causes an inwards steering torque on the front tire, and the rider has to counter-steer to keep the front tire from steering inwards.

At speeds below the self stable speed, a bike tends to fall inwards due to insufficient inwards steering, and the rider has to compensate by steering further inwards to maintain balance and lean angle.

At speeds above the self stable speed, called "capsize" mode, a bike with knife edge tires would tend to fall inwards at an extremely slow rate. With real tires, a bike tends to hold a lean angle with no perceptible tendency to fall inwards or straighten up. At these speeds, only counter-steering inputs can change lean angle.

Although motorcycle racers hang off a bike when turning for a variety of reasons, it's not needed when riding in a street situation.

 

[A.T.]

Recent video on counter-steering: