Quote:
Originally Posted by utopia
.....I think that there is more than one mechanism which can initiate a turn but that by far the main one is countersteering.
This causes gyroscopic precession of the front wheel with the result that it wants to tip into the turn by rotating about a horizontal axis at 90deg to the wheel spindle.
However, the front wheel cannot rotate in this manner because it is constrained by the tyre's contact with the ground and therefore it rotates about the contact patch instead.....
....ps. actually, gyroscopic precession forces wont be about a horizontal axis but one which is mutually at 90deg to both the wheel spindle and the steering axis .. but it would have got too wordy to include that bit in the above text)
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I’m struggling with your description of countersteering that produces gyroscopic precession of the front wheel rather than turning of the forks?
I think in terms of steady state, then action and corresponding reaction with imbalance of forces or moments producing accelerations (Change of speed and/or direction of travel).
Can you expand on that please?
Quote:
Originally Posted by utopia
Other inputs to the bike, like weight shifting or weighting one peg (essentially the same outcome via different methods) also contribute to the initiation of a turn, but these are supplementary to the main, countersteering input.
I guess what I'm saying is that although forces may want to act about their centres of rotation (spindle) or of mass (C of G) etc, the resultant outcome of these forces is that rotation must occur about the tyre's contact patch, because that is the only available option (as long as the wheels are on the ground.
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Shifting weight can also create a turn because a bike isn’t rigid, it has a hinge behind the front forks. Movement of the rider generates equal and opposite forces in the bike as it’s a closed system.
If you jerk your body weight sideways it causes the steering to turn slightly because it pulls the headstock to left or right (Slightly) relative to the contact patch. That is easily demonstrated when pushing a bicycle. If you couldn’t do this you couldn’t ride a bicycle “no hands”.
If you had vertical forks with no trail you wouldn’t be able to do this, but the bike would be pretty unrideable as there’d be no self centring of the steering either.