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utopia · 26-07-2019, 10:53 AM

I still disagree that the bike rotates about the centre of gravity when cornering.
Apart from the requirement for the contact patch to move sideways to allow this to happen, the tyre would also have to lift off the ground in order for the C of G to remain at the same height when the bike leans into a corner, and this clearly doesn't happen.
I don't believe that the contact patch moves sideways due to cornering forces either. Instead I think the lateral displacement of the tyre track after going through a puddle is generated by the trail of the front wheel. This initially shifts the front wheel contact patch sideways, and the castor effect then pulls it back in line, giving the straight-line steering stability observed to extreme in choppers with long forks and therefore increased trail.

Furthermore, I don't think it is entirely correct to state that the centrifugal/centripetal forces act solely through the C of G.
Every single element of mass contained in the motorcycle, from the sidestand at the bottom to the camera on top of the riders helmet experiences these forces. It is merely an expediency for the sake of calculation that they can be resolved into a single resultant that can be considered to act through the C of G.

There has been some talk about countersteering, but this is not really relevant to the discussion about the forces acting during the turn, it merely relates to the forces which initiate the turn in the first place.
However, while we're on the subject, countersteering does not actually involve turning the bars in the opposite direction at all. That is to say, there is no actual contra rotation of the steering. Instead, a force is applied in the contra direction but this causes the front wheel to lean.
The front wheel doesn't first turn the wrong way and then react to its "mistake" by leaning. It is one "holistic" process and involves no actual turning of the steering at all.

Finally in response to the "just get on and ride the thing" attitude .. yes, I kinda agree in many respects.
However I don't think the two ways of doing it are mutually exclusive.
That is to say, whether or not one claims to ride by feel alone, the physics is still going on and an analysis of how it operates can only compliment and enhance the riders' experience.

Oh and just to nit-pick slightly .. strictly speaking, a vector has direction and magnitude, where that magnitude is proportional to its length. Sorry, I am being a bit pedantic there, but science sometimes demands such pedantry.
Similarly, Newton said that a body will continue in a state of rest or uniform motion IN A STRAIGHT LINE unless acted upon by an external force.

If all the above sounds like I'm a know-it-all, I apologise and assure you that this is not the case.
I'm just as likely to sometimes talk cobblers as the next bloke.
But I hope my two-pennorth furthers the discussion.

26-07-2019, 10:53 AM	#34
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	I still disagree that the bike rotates about the centre of gravity when cornering. Apart from the requirement for the contact patch to move sideways to allow this to happen, the tyre would also have to lift off the ground in order for the C of G to remain at the same height when the bike leans into a corner, and this clearly doesn't happen. I don't believe that the contact patch moves sideways due to cornering forces either. Instead I think the lateral displacement of the tyre track after going through a puddle is generated by the trail of the front wheel. This initially shifts the front wheel contact patch sideways, and the castor effect then pulls it back in line, giving the straight-line steering stability observed to extreme in choppers with long forks and therefore increased trail. Furthermore, I don't think it is entirely correct to state that the centrifugal/centripetal forces act solely through the C of G. Every single element of mass contained in the motorcycle, from the sidestand at the bottom to the camera on top of the riders helmet experiences these forces. It is merely an expediency for the sake of calculation that they can be resolved into a single resultant that can be considered to act through the C of G. There has been some talk about countersteering, but this is not really relevant to the discussion about the forces acting during the turn, it merely relates to the forces which initiate the turn in the first place. However, while we're on the subject, countersteering does not actually involve turning the bars in the opposite direction at all. That is to say, there is no actual contra rotation of the steering. Instead, a force is applied in the contra direction but this causes the front wheel to lean. The front wheel doesn't first turn the wrong way and then react to its "mistake" by leaning. It is one "holistic" process and involves no actual turning of the steering at all. Finally in response to the "just get on and ride the thing" attitude .. yes, I kinda agree in many respects. However I don't think the two ways of doing it are mutually exclusive. That is to say, whether or not one claims to ride by feel alone, the physics is still going on and an analysis of how it operates can only compliment and enhance the riders' experience. Oh and just to nit-pick slightly .. strictly speaking, a vector has direction and magnitude, where that magnitude is proportional to its length. Sorry, I am being a bit pedantic there, but science sometimes demands such pedantry. Similarly, Newton said that a body will continue in a state of rest or uniform motion IN A STRAIGHT LINE unless acted upon by an external force. If all the above sounds like I'm a know-it-all, I apologise and assure you that this is not the case. I'm just as likely to sometimes talk cobblers as the next bloke. But I hope my two-pennorth furthers the discussion.