And John says,
adding weight at the rear contact patch won't change the flick at all ... because the "flick" is anchored at the rear patch.
Yes, the tire contact points are anchored to the ground in the sense of a hinge. And I think that's a useful point of view. But the forces that cause the "flick" or roll, will be affected by the distribution of mass. And yes, I sortof see your point of view.
But as you pointed out, the CoG is a single point in space that is affected by gravity or acceleration. And that is not the same as the hinge point. The forces of acceleration act on that singular center of gravity. The turning, or rolling, or torque effect of that is a function of the distance between the two points. Adding weight (or mass as I like to think of it) at the rear contact point *will* move that single point, the CG, lower and to the rear. Thus, the center of gravity will change. The point of rotation, which is the hinge point or contact point, will not. For emphasis, will not. My point is that the relation between the forces from acceleration acting on the mass of the bike and the geometry, will change due to the change of CG. Anytime you add mass (or weight) to a point other than the exact center of gravity will change the center of gravity.
The good thing about this thread is that it has got me thinking, and more aware of what really happens. If I ride straight ahead but weaving left and right, I can sense, can feel that longitudinal roll center. And it is not at the contact points. Now this is subjective as can be, and I'm not looking at my actual ground track. But If you do it just right, kindof like "lazy eights" in an airplane, that roll center becomes apparent. At least to me.
I used to fly a Piper Pawnee -- a cropduster. In that airplane the motor is at the front with a hopper and fuel tank behind, leaving the pilot seat way behing the CG. In most light aircraft, the CG is real near the pilot's seat, so it took a while to get used to my whole body swinging back and forth with the rudders. But the important thing there is to be able to feel that center of rotation. Some call it "seat of the pants" flying. And in an airplane, free to move in all axes, all rotations occur around the center of gravity.
I've also got to thinking about the notion of the unladen CoG. On a bicycle there are numerous techniques for cornering. I have long had this tendency to like to power my way out of a turn, but it is so easy to hit a pedal in a steep bank (or lean). I've gone ass over teakettle a couple of times doing that. Some say to coast through turns but that's no fun. So I've adopted a technique of leaning my body to the inside of the turn so the bike frame will stay more upright. That sortof works but is not real comfortable.
Likewise, you can plant yourself on the saddle and clamp your thighs and then your body mass becomes closely coupled to the bike. That's more motorcycle style. Otherwise if you stand on the pedals (or pegs), letting the bike move around below you, and just use countersteering technique (no leaning now), the bike will move underneath you in quite a different way. This latter case, I think, is about as close as you can come to experiencing the unladen CG as you can get -- unless you're riding freestyle.
And again, I hope this is a contribution and not more fodder for wattless controversy.
respectfully.........
)
