Did you ever play with a spinning bicycle wheel? The wheels used in physics demonstrations often has a heavier rim but the principles should be easily seen with a normal bicycle wheel.
At no point has anyone in the thread tried to support gyroscope effects being significant in bike riding. The OP just mentions having seen references to the idea and the “counter proofs” of bikes with extra counter rotating wheels, but this is just to give context to his question about how a counter rotating wheel would change anything.
Nope—countersteering applies to motorcycles and bicycles alike. This is uncontroversial in vehicle dynamics circles. The effect is much more perceptible on a motorcycle than on a bicycle because motorcycles are so much more massive than bicycles, but the equations of motion are identical between bicycles and motorcycles—it would be remarkable if they weren’t.
Oh hey, an area where I have some level of expertise! See my comments in this old thread. Or go right to the data.
In short, there is definitely a short countersteer before each turn. I have not analyzed every bit of the dynamics, but I posit that countersteering is always required, and is simply ingrained in learning to ride a bike. It’s just not very apparent most of the time due to the low mass of the bike compared to the rider. The weight shift induces the countersteer, rather than the opposite (as with a heavy motorcycle).
And my experiments conclusively proved the opposite. The only “countersteer” before a turn on a bicycle is the last oscillation of the continual slight back-and-forth inherent in “straight” forward motion.
If you’re going straight on a bike, and adjust your grip such that each hand can only push, not pull, on the handlebar, and then let go with your left hand (so that you’re pushing the right bar forward), you will turn to the left.
How do you know the handlebars didn’t push on you?
The countersteer was subtle. Even with the rotary encoder, it was hard to notice in shallow turns, because it only takes a very small amount to initiate such a gradual lean.
You should be able to steer the bicycle somewhat without touching the handlebars at all…
I never claimed (not having performed detailed calculations or experiments) gyroscopic torque has absolutely zero effect on the response of a bicycle; it probably makes it easier to ride but does not seem to be absolutely essential?
I attempted to gather data while riding hands-free (I got to be reasonably good at this in college, and can easily ride a few miles through twists and turns without touching the handlebars). However, the data was inconclusive. The turns were too shallow for any induced countersteer to be obvious. The turns themselves barely showed up.
If I had access to a giant, smooth, empty parking lot, I could collect better data, but I didn’t manage to find a good place near me.
How fast? Counter-steering only takes over above a certain speed.
Folly- Motorcycle and bicycle rider
…I do know the handlebars pushed on me. Because I pushed on them, and Newton’s Third Law. But they only pushed on the part of me that was in contact with them.
I mean before you pushed on them.
You are suggesting that because you have arranged things so that when you move the handlebars from (say) 0° to 5°, that there could not have been a period where they were at -1°, since you were only ever applying force in the positive direction. But this ignores the possibility that shifting your weight caused the handlebars to push back, and that the amount was too small for you to notice.
I am surprised this has not been posted (unless I missed it…I searched for it here).
Bikes are quite surprising. Gyroscopic forces (conservation of angular momentum) have only a little to do with keeping them upright (and probably not for the reasons you think).
Bottom line: It is still a bit of a mystery.
It’s required at all speeds; it’s just that at very low speeds, the steering input forces and displacements are so subtle that it’s easy to not notice them. Check out the plot halfway down this page: for a bicycle at about 13 MPH, the countersteer input torque on the bars is just 0.25 N*m, which works out to a push of about 0.5 N (about 1.8 ounces) on one of the handlebars. The countersteer movement of the handlebars is just 0.5 degrees, and it’s over in a fraction of a second before you turn the bars back toward the direction the bike ends up leaning.
Thanks to the self-stabilizing steering geometry, the countersteer still happens even when your hands aren’t on the bars. When traveling upright in a straight line, leaning your body off to one side causes the bike to lean to the other side. This should not be surprising to anyone.
But I’ve been fiddling with the numbers in a spreadsheet lately, trying to verify what I’ve long suspected (that the bike lean and rider lean cancel each other out perfectly, leaving the rider+bike center of mass parked directly above the contact patches), and came to a surprising conclusion: for the range of masses and mass distributions of a typical rider and bicycle or motorcycle, the above-described weight shift causes the entire rider+bike system to lean in the direction the bike (not the rider) is leaning. The final outcome is still the same: the bike’s self-stabilizing steering geometry steers the bars in the direction the bike is leaning (this is the self-induced countersteer), getting the contact patches out from under you and back under the bike - at which point the whole rider+bike system is leaning in the direction of the rider, and now the rider’s intended turn finally begins.
My surprising conclusion - that the rider+bike system ends up leaning in the direction opposite to which the rider hangs off - is related to the mass moments of inertia of the rider and bike with respect to rotation around an axis defined by the two tire contact patches, and also to the heights of the centers of mass of the rider and the bike. Basically, if the bike/motorcycle’s center of mass is positioned significantly below that of the rider, then body english will initially make the whole system lean in the direction of the bike, unless the mass distribution is really bizarre (e.g. concentrate half the mass of the bike at the height of the handlebars and the other half down at ground level, leaving the center of mass at the original height but creating a weirdly large mass moment of inertia).
OK. I’ll buy that it’s only noticeable above a certain speed.
And I still maintain that the tiny steerings you’re referring to there are not part of the turn at all, since you also get such tiny steerings when driving “straight”.
I assume that a bike with a fixed front wheel, where the front wheel doesn’t steer at all, would be more or less unrideable.
That’s quasi-reasonable. But it just puts this in the same category as, say, airplane wings: while the physics is unambiguous, the accounting of behavior to some physical effect becomes very fuzzy. The behavior of wings is variously assigned to Bernoulli, Coanda, turbulence, simple momentum transfer, etc. In reality it’s just F=ma, but there are many special-case effects that can overlap in any given circumstance and they become impossible to separate.
If you want to lump these tiny steerings into “general bicycle self-stability”, sure, but that doesn’t mean a different accounting would find the same thing. It also leaves open the question of why explicit countersteering is necessary for sharp turns but not shallower ones.
I’d like to do some experiments on riderless bikes given a shove. A couple questions I’d like answered: does a countersteer show up in those cases as well? And does the magnitude of the shove correspond to the new velocity of the bike, or did the bike extract additional momentum from the Earth the way a ridden bike does?
Yes, it’s totally unstable. Though I’m curious what happens with a riderless bike that can turn right but not left. My guess is that it either tips over or finds itself on a stable right-bearing path with some probability, but I’d like to see the experiment.
Not necessarily true. See the video I posted in #93 above. They show stable bikes with steering in the rear (and other unlikely setups that work).
Or even a ridden bike. Would you be able to turn left at all? If you started a turn to the right, would you be able to bring the bike back up to go straight?
This experiment needs to be performed with younger people with less brittle bones than I have.
Fair enough, but I was imagining starting with a bike with a fixed rear wheel, and welding the front handlebars into a fixed position, meaning neither of them can steer.
The rear wheel turning would certainly change how it handles, but it is still allows the direction to change to keep the contact patch under the center of gravity. I noted that video had an example of a ridden bike, but not a riderless bike with rear steering. Just as adding weight to the front wheel behind the fork makes it unstable riderless, while it is still possible to ride, I’d assume that the rear steering also needs a human to overcome the instabilities created in that situation.
Watch the video (it is not long). They have contraptions like you describe that are riderless and stable.