Quote:
Originally Posted by Ken Fry
I think Sendler's answers here are already quite good. This might be simpler... maybe:
The bike, of course "knows" nothing, but the whole system functions as a feedback loop.
The bike knowing how much to countersteer and knowing how hard the wind is pushing are interrelated: the sideward component of the crosswind causes a countersteering force: the more the wind force, the greater the countersteering effect. (The bike is designed to do what a rider would otherwise have to do.)
The bike stops countersteering when equilibrium is established. A cross wind from the left causes countersteering to bank the bike to the left. The bank to the left, however causes countersteering (from gravitational effects)* to tend to lift the bike back up to vertical. Equilibrium is established when the two tendencies are balanced.
Obviously, for this to work, the bike has to be well-designed (from this perspective), and the rider has to avoid tensing up and applying a white knuckle grip. There have been bikes that will oscillate (all the way up to tank slappers) at the slightest provocation, so motorcycling handling dynamics are not as simple as they might appear.
* You can see this effect if you straddle a bike and tilt it to the right. The handlebars steer to the right without your input.
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I do not dispute the effects that both you and sendle discribe.
So we have all accepted that the wind force from the left is causing the bike to roll to the right, about a roll axis; which is at the ground level along a line that goes between the contact patches of the front and rear wheels.
The issue can be reduced to the sum of the moments in the wind direction [to the right or clockwise] and the sum of the moments to the left [oposite to the wind direction and to the left, or counterclock wise].
The moments to the right [clockwise] are due to the wind, gravity and a small amount of prosesion caused by the rear wheel that cuases a yawing moment about the vertical axis to the right.
The moments to the left [counterclockwise ]are due to trail and procesion as the front wheel is rotated about the steering axis.
It is my contention that the sum of the moments in the clockwise direction
[due to wind and gravity]; without rider steering input, will always be greater than the sum of the moments in the counterclockwise direction [due to trail and prosesion].
Therefore bikes are not self corecting