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  #1  
Old 02-15-2017, 08:22 PM
lesizz lesizz is offline
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Why is it easier to balance on a moving bike than a non-moving one (revisited)?

Yes, TRAIL!

But why?

The real balance mechanism is the rider's brain. The brain has built into it a feedback servo system that works in the background (subconscious). When walking, a person's (or chihuahua's) brain will sense via physical senses when the body starts a micro-tilt in one direction, and compensate by using the muscular to offset that tilt with a forced tilt in the opposite direction.

Same thing with riding a bike, except that the response mechanism is the steering. A micro-tilt in one direction will be compensated by the brain with a micro-steer to do an offsetting tilt in the opposite direction. This is why if your front wheel loses traction, you crash. Period. Unless you do a lightning-fast forced recovery. If you are following another bike and your front wheel touches the bike in front, you crash. Probably.

The reason a positive trail bike can't be made to work by a human is that apparently our servo's are equipped to work with negative trail but not with the commanding adjustment in the opposite polarity. A driveless bike controlled by a computer could be programmed to work with any trail you would wish.
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  #2  
Old 02-15-2017, 08:47 PM
cochrane cochrane is offline
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Link to the article.
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  #3  
Old 02-15-2017, 09:21 PM
Musicat Musicat is offline
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In spite of Karen's article, the gyroscopic effect may be less important than is commonly thought:
Quote:
On the other hand, it has also been shown that the gyroscopic effect of a bicycle’s wheel is all but cancelled out by the weight of the rider’s body as well as the force pushing down on the front handlebars. One ambitious engineer, Dr. Hugh Hunt of the University of Cambridge, built a bike with a second front wheel. Theoretically, if gyroscopes were all that had to do with balance, spinning the second wheel in the opposite direction of the first would cancel out the gyroscopic forces, and make the bike un-rideable. Yet no matter how fast the second wheel was spun, the bike performed exactly the same. This, he concluded, demonstrated that while gyroscopes are part of a bicycle’s movement, their effect on stability is small enough that it is overshadowed by the force of the rider’s weight and movement.
also:
Quote:
Gyroscopic forces are not important for the stability of a bicycle...but they help us to control the bike when riding with no hands. More important than anything is "the trail". The front wheel makes contact with the pavement at a point that lies behind the point where the steering axis intersects with the pavement - and the distance between these is called the trail.
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  #4  
Old 02-16-2017, 12:03 AM
scr4 scr4 is offline
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Originally Posted by lesizz View Post
The reason a positive trail bike can't be made to work by a human is ...
Do you have a cite for this? (That a positive trail bike cannot be ridden by a human?)
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  #5  
Old 02-16-2017, 03:42 AM
watchwolf49 watchwolf49 is offline
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I tried the right hand rule but I got my thumb caught in the spokes ... Karen should have warned us about that ...
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  #6  
Old 02-16-2017, 04:29 AM
naita naita is offline
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Originally Posted by scr4 View Post
Do you have a cite for this? (That a positive trail bike cannot be ridden by a human?)
Here's a cite to the contrary:
Quote:
The common view is that this self-steering is caused by gyroscopic precession of the front wheel, or by the wheel contact trailing like a caster behind the steer axis. We show that neither effect is necessary for self-stability.
http://science.sciencemag.org/content/332/6027/339
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  #7  
Old 02-16-2017, 05:00 AM
snowthx snowthx is offline
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I thought a bike could not stand on it's own because it is two tired.
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  #8  
Old 02-16-2017, 05:34 AM
standingwave standingwave is offline
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Kinda related... From Smarter Every Day. What happens when the steering is reversed on a bicycle? Answer: It can't be ridden. At least not easily and not until you've forgotten how to ride a normal bike:

The Backwards Brain Bicycle: https://youtu.be/MFzDaBzBlL0

I don't think I ever truly understood countersteering until I was riding street motorcycles.It was just something I always took for granted.
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  #9  
Old 02-16-2017, 02:32 PM
Chronos Chronos is offline
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Most bicycle riders don't understand countersteering for the simple reason that it's not something that you do on a bicycle at all. I've done the experiments to verify it.
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  #10  
Old 02-16-2017, 03:36 PM
Irishman Irishman is offline
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Quote:
Originally Posted by lesizz View Post
The reason a positive trail bike can't be made to work by a human is that apparently our servo's are equipped to work with negative trail but not with the commanding adjustment in the opposite polarity. A driveless bike controlled by a computer could be programmed to work with any trail you would wish.
People can learn to ride negative trail bikes. The difficulty is that they are inherently more unstable than positive trail. Trail is self-correcting. As you start to move in one direction (turn), the trail follows the turn automatically. A negative trail bike is like trying to balance a broom on your nose. People can do it, but it takes a lot of practice to learn how to counter the small imbalances.

Compare balancing a pencil on your finger to holding the pencil by the tip and letting it hang down. It hangs down straight automatically, but balancing requires you to shift your finger around to compensate for small disturbances. That's positive vs negative trail.

Musicat, apparently you didn't follow the link at the top of the column to the follow up report, which says the same thing you did.

http://www.straightdope.com/columns/...-one-revisited

Quote:
Originally Posted by standingwave View Post
I don't think I ever truly understood countersteering until I was riding street motorcycles.It was just something I always took for granted.
Quote:
Originally Posted by Chronos View Post
Most bicycle riders don't understand countersteering for the simple reason that it's not something that you do on a bicycle at all. I've done the experiments to verify it.
Yes, when riding a bicycle, the forces are small enough to be overcome by your steering. Motorcycles are much heavier and require countersteering.

However, you can find countersteering if you ride a bicycle with no hands.

http://www.sheldonbrown.com/brandt/gyro.html
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  #11  
Old 02-16-2017, 05:03 PM
standingwave standingwave is offline
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Quote:
Originally Posted by Chronos View Post
Most bicycle riders don't understand countersteering for the simple reason that it's not something that you do on a bicycle at all. I've done the experiments to verify it.
Agree to disagree.
You may not realize that you intuitively countersteer every time you enter a corner. However, once you are aware of this concept it’s much easier to control and perfect.
To initiate countersteering, momentarily turn away from the direction you’re turning. This increases the lean of the bicycle into the turn. This method allows for greater steering control and makes it easy to affect a change in direction during the turn.
https://cyclingtips.com/2009/10/cornering-tips/

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  #12  
Old 02-16-2017, 05:47 PM
Chronos Chronos is offline
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Again, I've done the experiment. I positioned my hands on the handlebars such that they could only push, not pull, and then I removed my left hand (so I was pushing only on the right bar, and hence rotating it only counterclockwise). Result, I turned left, just as someone who'd never heard of countersteering would expect.
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Old 02-16-2017, 06:37 PM
Dr. Strangelove Dr. Strangelove is offline
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How did you eliminate the effect from shifting your body's weight? If you instinctively leaned into the turn and the handlebars pushed back slightly, you probably wouldn't notice.

I'm tempted to install a rotary encoder on my bike's steering and record some no-hands riding.
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  #14  
Old 02-16-2017, 07:46 PM
Xema Xema is offline
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Quote:
Originally Posted by Chronos View Post
I turned left, just as someone who'd never heard of countersteering would expect.
It's easy to mask countersteering if you want only small steering changes: the bicycle regularly tilts slightly from side to side, so you just wait until it tilts the way you want, and go with it.

But more pronounced direction changes require countersteering. If you push the right handlebar briskly forward, you will definitely lean left; you must then either do the opposite to continue along your former track, or accept the left lean (by turning the handlebars left) and watch yourself turn left.
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  #15  
Old 02-16-2017, 08:04 PM
Xema Xema is offline
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Here's Wiki on countersteering:
Quote:
When countersteering to turn left, the following is performed:

A torque on the handlebars to the right is applied.
The front wheel will then rotate about the steering axis to the right and the tire will generate forces in the contact patch to the right.
The machine as a whole steers to the right
Because the forces in the contact patch are at ground level, this pulls the wheels "out from under" the bike to the right and causes it to lean to the left.
The rider, or in most cases the inherent stability of the bike, provides the steering torque necessary to rotate the front wheel back to the left and in the direction of the desired turn.
The bike begins a turn to the left.

While this appears to be a complex sequence of motions, it is performed by every child who rides a bicycle. The entire sequence goes largely unnoticed by most riders, which is why some assert that they do not do it.
The Wiki article includes this interesting quote:
Quote:
Originally Posted by Wilbur Wright
I have asked dozens of bicycle riders how they turn to the left. I have never found a single person who stated all the facts correctly when first asked. They almost invariably said that to turn to the left, they turned the handlebar to the left and as a result made a turn to the left. But on further questioning them, some would agree that they first turned the handlebar a little to the right, and then as the machine inclined to the left, they turned the handlebar to the left and as a result made the circle, inclining inward.
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  #16  
Old 02-16-2017, 09:22 PM
Chronos Chronos is offline
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Pushing the right handlebar forward is turning the handlebars left.
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  #17  
Old 02-17-2017, 07:17 AM
thelikesofdave thelikesofdave is offline
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What about ski bikes? they work fine!

It is because you can steer into a fall thereby keeping yourself upright.

The gyroscope effect is mumbojumbo

Here is a ski bike that proves the point:
https://www.youtube.com/watch?v=mT6pDvkmtFM
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  #18  
Old 02-17-2017, 07:55 AM
scr4 scr4 is offline
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Quote:
Originally Posted by Chronos View Post
Again, I've done the experiment. I positioned my hands on the handlebars such that they could only push, not pull, and then I removed my left hand (so I was pushing only on the right bar, and hence rotating it only counterclockwise). Result, I turned left, just as someone who'd never heard of countersteering would expect.
If you were going straight and balanced, then suddenly turned the steering wheel to the left, the front wheel goes to the left, the center of mass will end up on the right side of the wheels, and you will fall down to your right.

What you actually did was to wait till you were already leaning to the left, and then turn the handlebar to the left. You can then maintain balance through a left turn by varying the amount of left steering input.

Counter-steering is far more obvious on a recumbent bike, where the rider's upper body is less mobile. It's also very obvious on long-wheelbase bikes like tandem bikes. So it was very obvious on my tandem recumbent bike. But even then, it wasn't something I did consciously. It's an automatic reflex for anyone who knows how to ride a bicycle.

Last edited by scr4; 02-17-2017 at 07:58 AM..
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  #19  
Old 02-17-2017, 09:30 AM
Chronos Chronos is offline
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If you're going straight and suddenly turn the handlebars left, the result won't be turning left or turning right. It'll be that you fall down.

If you manage to recover from the fall, it'll be by turning the other direction. In that sense, countersteering makes it necessary to steer the correct way. But steering the correct way doesn't require countersteering.
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  #20  
Old 02-17-2017, 09:40 AM
scr4 scr4 is offline
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Quote:
Originally Posted by Chronos View Post
If you manage to recover from the fall, it'll be by turning the other direction. In that sense, countersteering makes it necessary to steer the correct way. But steering the correct way doesn't require countersteering.
That is the correct way to steer a bicycle. You initiate a turn by creating a slight imbalance, so that you+bicycle are leaning towards the turn. It may not be a conscious or even visible amount of countersteer - often it's done by just waiting for the imbalance to occur and letting it build up to the desired amount.

Last edited by scr4; 02-17-2017 at 09:43 AM..
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  #21  
Old 02-17-2017, 09:42 AM
Quercus Quercus is offline
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I think the Dope Staff should update this article. It's pretty clear that for humans riding bicycles, gyroscopic forces are mostly insignificant. Evidence includes calculation of the forces, and practical demonstrations of various bicycle-like devices with no gyroscopic effect (ski-bikes and the test bicycle with an extra counter-rotating wheel in front) that are able to be ridden perfectly well with the same technique as standard wheeled bicycles. (The gyroscopic forces are strong enough to help balance a unattached wheel or hoop rolling by itself, but not enough to affect a bicycle with rider.)

The main reason one can balance on a moving bike is that with forward motion and steering, the rider can move the bicycle wheels back under their center of mass (quicker than bicycle falls over). Negative trail, where the geometry is such that the wheel naturally turns to correct a lean, helps the rider balance, but it's not completely necessary. Evidence for this is that bikes with positive trail can be ridden, but it's much harder.
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  #22  
Old 02-17-2017, 09:55 AM
Quercus Quercus is offline
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Quote:
Originally Posted by Chronos View Post
Again, I've done the experiment. I positioned my hands on the handlebars such that they could only push, not pull, and then I removed my left hand (so I was pushing only on the right bar, and hence rotating it only counterclockwise). Result, I turned left, just as someone who'd never heard of countersteering would expect.
Quote:
Originally Posted by Dr. Strangelove View Post
How did you eliminate the effect from shifting your body's weight? If you instinctively leaned into the turn and the handlebars pushed back slightly, you probably wouldn't notice.
I think Strangelove is probably right, here. It's really difficult for humans to consciously notice all the little tiny shifts of balance that happen and the unconscious corrections. And so it's really easy for humans to take advantage of a momentary lean without realizing it.

I mean, do the physics, Chronos. If a perfectly upright bicycle was rolling forward and the front wheel was steered to the left, the front of the bicycle would move to the left, putting the center of gravity on the right side of the wheels. And there's no possible source of torque to keep everything from falling over to the right.
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  #23  
Old 02-17-2017, 09:59 AM
scr4 scr4 is offline
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Originally Posted by Quercus View Post
The main reason one can balance on a moving bike is that with forward motion and steering, the rider can move the bicycle wheels back under their center of mass (quicker than bicycle falls over). Negative trail, where the geometry is such that the wheel naturally turns to correct a lean, helps the rider balance, but it's not completely necessary. Evidence for this is that bikes with positive trail can be ridden, but it's much harder.
Exactly!

Too much trail can also be a problem because it tries to over-correct for the lean - usually referred as "wheel flop." The rider is constantly having to fight against it.
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  #24  
Old 02-17-2017, 11:24 AM
Xema Xema is offline
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Originally Posted by Xema View Post
If you push the right handlebar briskly forward, you will definitely lean left
As Chronos has noted, I got this wrong - should be "If you push the left handlebar briskly forward ..."
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  #25  
Old 02-17-2017, 11:29 AM
Xema Xema is offline
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Originally Posted by Chronos View Post
If you're going straight and suddenly turn the handlebars left, the result won't be turning left or turning right. It'll be that you fall down.
True, for certain values of "suddenly".

If you do this just a bit less suddenly, you have initiated a turn to the right.
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  #26  
Old 02-17-2017, 02:00 PM
EdelweissPirate EdelweissPirate is offline
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Originally Posted by Chronos View Post
If you're going straight and suddenly turn the handlebars left, the result won't be turning left or turning right. It'll be that you fall down.

If you manage to recover from the fall, it'll be by turning the other direction. In that sense, countersteering makes it necessary to steer the correct way.
This is exactly the definition of countersteering. Turning the bars initiates a fall and then that fall is "caught" by the lateral acceleration of a turn in the opposite direction.

Quote:
Originally Posted by Chronos View Post
But steering the correct way doesn't require countersteering.
Oh, but it does. This is a settled question in the field of vehicle dynamics.

The classic experience that drives this home to most people is finding oneself an inch or so from the curb or the edge of the pavement. It's very hard to move away from that edge. If one could initiate a lean (and thus a turn) without countersteering, it would be easy: just do it. But it's hard because there's no room for the required countersteer toward the curb that initiates the turn away from the curb or rut. One must instead edge away slowly, which is regular turning but with very small-amplitude countersteering.

One can countersteer weakly by shifting one's weight, which is how one initiates a turn when riding hands-free.

Chronos, I agree with Dr. Strangelove and Quercus: your experiment, laudable though it may have been, was likely contaminated by subconscious weight-shift countersteering. And Quercus raises an important point: if countersteering wasn't responsible for shifting your center of mass out of vertical alignment with your tire contact patch, what was?

I don't mean to go all Clever Hans on you, but human beings are terrible data acquisition devices. A subconscious hip-shimmy seems more likely than the discovery of an previously unknown steering mechanism for two-wheeled vehicles.
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  #27  
Old 02-17-2017, 02:13 PM
EdelweissPirate EdelweissPirate is offline
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Originally Posted by Quercus View Post
I think the Dope Staff should update this article. It's pretty clear that for humans riding bicycles, gyroscopic forces are mostly insignificant.
I concur. While the article contains a prominent link to an updated article (and a less-wrong one to boot), we're still left with a staff report that gives the wrong answer. While Karen's mea culpa in the updated article is just fine, wouldn't it make more sense to delete this article and append its text to the corrected version?

Failing that, an explicit disclaimer at the top of this article would be helpful. Currently, we've just got "please see the update to this article," which doesn't really convey that the current article is just wrong. Something like: "Correction: this staff report contains a major error; see this link for a more accurate answer."

I'm sure someone can come up with a more succinct blurb. But as it stands, this article is less "ignorance fought" than "ignorance promulgated."
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  #28  
Old 02-17-2017, 08:51 PM
Chronos Chronos is offline
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The classic experience that drives this home to most people is finding oneself an inch or so from the curb or the edge of the pavement. It's very hard to move away from that edge. If one could initiate a lean (and thus a turn) without countersteering, it would be easy: just do it. But it's hard because there's no room for the required countersteer toward the curb that initiates the turn away from the curb or rut. One must instead edge away slowly, which is regular turning but with very small-amplitude countersteering.
Which proves nothing, because there's also no room for steering away.

Quote:
Chronos, I agree with Dr. Strangelove and Quercus: your experiment, laudable though it may have been, was likely contaminated by subconscious weight-shift countersteering. And Quercus raises an important point: if countersteering wasn't responsible for shifting your center of mass out of vertical alignment with your tire contact patch, what was?
So you're saying that countersteering was the only possible way I could have shifted my weight, and that my shifting my weight was what caused the countersteering. Which one do you assert caused the other?
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  #29  
Old 02-17-2017, 11:09 PM
scr4 scr4 is offline
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Originally Posted by Chronos View Post
So you're saying that countersteering was the only possible way I could have shifted my weight, and that my shifting my weight was what caused the countersteering. Which one do you assert caused the other?
What do you mean by "shifting my weight was what caused the countersteering"? I didn't think anyone claimed that.
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Old 02-18-2017, 07:13 AM
Chronos Chronos is offline
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EdelweissPirate said it right there: Subconscious weight-shift countersteering.
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  #31  
Old 02-18-2017, 08:35 AM
scr4 scr4 is offline
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Well, obviously it is possible to affect steering or weight shift without touching the handlebars, otherwise nobody could ride a bicycle hands-off. But weight shift requires external force, so it's not as simple as "move your upper body to the right to shift your weight to the right."

I think the only available force is the traction of the tires: when you move your upper body to the right, you are really bending your body, and pushing with your feet/tires towards the right. This is a very weak mechanism, and obviously not a dominant control mechanism for a bicycle - if it were, it would be just as easy to take a bicycle, lock its handlebars, and balance on it (stationary) without using your hands.

ETA: thinking about it more, it's possible that when riding hands-off, the lateral force (generated by bending your body) is not shifting your weight, but actually generating steering input through trail. (Bend your body to the right, which pushes tires to the right, and trail converts this lateral force into a rightward steering input.) This explains why some bicycles are much easier to ride hands-off than others.

Last edited by scr4; 02-18-2017 at 08:37 AM..
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  #32  
Old 02-18-2017, 08:46 PM
Dr. Strangelove Dr. Strangelove is offline
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Originally Posted by Chronos View Post
Which one do you assert caused the other?
It works both ways. Just as how on a fixie bike, your legs can drive the pedals or the pedals can drive your legs.

If you wish to turn right hands-free, you must tilt both your body and the bike to the right. But first you must tilt your body, and due to good old Newton, that means applying force to the bike to the left. Due to trail, this will manifest as a subtle turn to the left.

One way of looking at it is that the angular force along the bike's axis and the steering input are tied together. How is it that a bike leaning into a turn stays upright? Answer: centrifugal force counteracts the force of gravity on the bike and rider. How is it that the bike experiences centrifugal force? Answer: it's traveling on a curved path. Why is the bike traveling on a curved path? Answer: the front wheel is steered in that direction.

So there's a direct relationship between the two, but it's not limited to already being in a turn. If you wish to make a right turn, you must first get the bike tilted in that direction. And if you're currently upright, then you must apply a torque along the axis. Applying a torque to the right requires first steering left.

This can be done gently, even imperceptibly: a very tiny input starts the tilt, and after that you lag the amount you need to stay upright. For instance, say you steer left by 0.5°. The bike starts tilting over, and once it's 10° over it requires a 5° steering input to counteract gravity. But you've only steered by 4.5°, and so the bike tilts farther. It hits 20°, which requires a 10° input, but you're only applying 9.5°. And so on, until you reach the desired angle.

If you wish to turn quickly, this can be done all at once. You apply an aggressive countersteer until you are at the desired level, and then you apply steering appropriate for the turn. This is more difficult since the transition is harder, but the principle is the same. And it's utterly necessary for anyone doing "serious" bicycling, like BMX.

All of this is symmetrical. If you ride hands-free, then you must first tilt in the appropriate direction to make a turn. And tilting in that direction requires first accelerating the bike in the opposite direction, which will naturally cause some countersteer. But it's going to be a very subtle effect.

You might imagine that you could do it purely with weight shifting. If you simply locked the handlebars from turning left at all, you could get the bike tilted over without the countersteer. But you still applied a countersteer force; it just happened to be blocked. And most likely you fell on your ass before doing anything, because it would be impossible to ride such a bike in a straight line.

I have a rotary encoder on order. Hopefully it's precise enough to show the effect. Might be a few weeks before I have the time to set it up, though.
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  #33  
Old 02-19-2017, 04:35 PM
Melbourne Melbourne is offline
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Originally Posted by scr4 View Post
If you were going straight and balanced, then suddenly turned the steering wheel to the left, the front wheel goes to the left, the center of mass will end up on the right side of the wheels, and you will fall down to your right.

What you actually did was to wait till you were already leaning to the left, and then turn the handlebar to the left. You can then maintain balance through a left turn by varying the amount of left steering input.

Counter-steering is far more obvious on a recumbent bike, where the rider's upper body is less mobile. It's also very obvious on long-wheelbase bikes like tandem bikes. So it was very obvious on my tandem recumbent bike. But even then, it wasn't something I did consciously. It's an automatic reflex for anyone who knows how to ride a bicycle.
Alternatively, you turned the stearing wheal to the left, the front wheel goes to the left, the center of mass ends up on the rights side of the wheels, and you maintained ballance by leaning to the left.

If it takes both actons to execute a turn, and they have to happen simultainously, it can't matter which one is "first".


People on heavier bikes may choose to counter-steer to throw the bike over, but it's not the only meathod of doing so.
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Old 02-19-2017, 04:44 PM
Melbourne Melbourne is offline
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Originally Posted by Quercus View Post
I think Strangelove is probably right, here. It's really difficult for humans to consciously notice all the little tiny shifts of balance that happen and the unconscious corrections. And so it's really easy for humans to take advantage of a momentary lean without realizing it.

I mean, do the physics, Chronos. If a perfectly upright bicycle was rolling forward and the front wheel was steered to the left, the front of the bicycle would move to the left, putting the center of gravity on the right side of the wheels. And there's no possible source of torque to keep everything from falling over to the right.
Actually, the centre of balance of your body is in a different position than the centre of balance of the system, which allows you shift the relationship between the centre of balance of the system, and the centre of balance of the earth.

And if there was indeed "no possible source of torque", the bicycle would be stationary. The brakes and the motor may both be used when turning a motorcycle, and I suggest that the same is true of a bicycle.
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Old 02-19-2017, 05:45 PM
EdelweissPirate EdelweissPirate is offline
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Originally Posted by Chronos View Post
Which proves nothing, because there's also no room for steering away.
I didn't say it proved anything, only that many people found the experience compelling.

I'm not sure I follow your point about there being no room for steering away. That might be true in the case of a curb, but this happens whether the thing you're steering away from is a "positive" feature (a curb that sticks up) or a "negative" feature (such as an abrupt drop-off in the pavement). What's limiting the room for steering away from a negative feature if, as you suggest, no movement toward the feature whatsoever is necessary to steer away from it?

Quote:
So you're saying that countersteering was the only possible way I could have shifted my weight, and that my shifting my weight was what caused the countersteering. Which one do you assert caused the other?
You're right; we've been imprecise in our choice of terminology. For lack of a better term, let's use "body english" to mean a motion that changes the angle of the bicycle relative to the plane of the road without moving the system's center of mass. We can then use "weight shift" to mean the state of having the system's center of mass no longer directly above the tire contact patch.

I'm suggesting that you used subconscious body english to lean the bike. As a result of this motion, trail caused the bike to steer opposite the direction of the intended turn. Momentum then tilted you back the other way (high-sided, in the parlance of our sport) such that the center of mass was no longer directly over the tire contact patch and you began turning normally.

The reason I believe this is what happened is because this is what conventional vehicle dynamics says is happening, and it jibes with my personal understanding of the dynamics. I find Chronos' knuckle-steer experiment uncompelling, and I gather he feels the same way about my account. Fair enough.

But really, Chronos, if you think you've legitimately found something that doesn't agree with the currently accepted theory, you've got a a paper to publish, don't you?

If you're not just playing devil's advocate, then, how is it that you move the center of mass out from directly above the contact patch without countersteering?
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  #36  
Old 02-19-2017, 05:49 PM
EdelweissPirate EdelweissPirate is offline
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Originally Posted by Melbourne View Post
And if there was indeed "no possible source of torque", the bicycle would be stationary. The brakes and the motor may both be used when turning a motorcycle, and I suggest that the same is true of a bicycle.
I understood Quercus to mean that there was no possible source of torque about the bicycle's axis of travel, not that there was no torque at the brake disc or the rear wheel. That said, I think turning from a steady-state travel is complicated enough without adding in acceleration or deceleration.
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  #37  
Old 02-19-2017, 05:53 PM
EdelweissPirate EdelweissPirate is offline
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Originally Posted by Dr. Strangelove View Post

I have a rotary encoder on order. Hopefully it's precise enough to show the effect. Might be a few weeks before I have the time to set it up, though.
Oooh! That's exciting!

I think your post articulated the argument I'm trying to make better than I did. Do keep us posted on your adventures with the encoder!
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  #38  
Old 02-19-2017, 06:37 PM
Chronos Chronos is offline
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Quote:
But really, Chronos, if you think you've legitimately found something that doesn't agree with the currently accepted theory, you've got a a paper to publish, don't you?
I maintain that it's not the currently-accepted theory, in that a theory must be well-tested, and so far as I can tell, this whole countersteering thing is barely tested at all. Most of what passes for "proofs" of countersteering is silliness like welding the fork of a bike in place and then finding that it's impossible to steer. I agree that my own experimental test is simplistic, but it agrees with the intuitive notion of steering, and I've yet to see anyone show any more sophisticated experiment that doesn't.
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  #39  
Old 02-19-2017, 09:04 PM
Xema Xema is offline
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Do you agree with the following?
1. Normal straight-line progress on a bike is a continuous process of noticing that the bike is starting to tilt left or right, then turning the front wheel to that side to counteract the tilt.
2. A normal turn requires that the bike lean in the direction of the turn, and that the rider maintain the lean until the turn is complete, at which point the upright position of #1 must be re-established.
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  #40  
Old 02-20-2017, 06:37 AM
Chronos Chronos is offline
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I'd quibble that the driver doesn't usually notice the slight tilts in #1, and instead corrects for it through a combination of automatic human balance reflexes and automatic trail stabilization effects, but other than that, sure.
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  #41  
Old 02-20-2017, 08:14 AM
Xema Xema is offline
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So it follows that to turn you must establish and maintain a lean - yes?
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  #42  
Old 02-20-2017, 08:47 AM
scr4 scr4 is offline
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I suggest another test: Next time you have some snow on the roads, ride straight, then turn. Inspect the tire tracks. I think you'll find that the front tire track first moves to the opposite direction of the turn.

The same test may be possible on a dry road by first riding through a puddle.
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  #43  
Old 02-20-2017, 08:15 PM
Irishman Irishman is offline
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Originally Posted by Xema View Post
It's easy to mask countersteering if you want only small steering changes: the bicycle regularly tilts slightly from side to side, so you just wait until it tilts the way you want, and go with it.

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Originally Posted by scr4 View Post
That is the correct way to steer a bicycle. You initiate a turn by creating a slight imbalance, so that you+bicycle are leaning towards the turn. It may not be a conscious or even visible amount of countersteer - often it's done by just waiting for the imbalance to occur and letting it build up to the desired amount.

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Originally Posted by Quercus View Post
I think Strangelove is probably right, here. It's really difficult for humans to consciously notice all the little tiny shifts of balance that happen and the unconscious corrections. And so it's really easy for humans to take advantage of a momentary lean without realizing it.
Quote:
Originally Posted by Xema View Post
Do you agree with the following?
1. Normal straight-line progress on a bike is a continuous process of noticing that the bike is starting to tilt left or right, then turning the front wheel to that side to counteract the tilt.
2. A normal turn requires that the bike lean in the direction of the turn, and that the rider maintain the lean until the turn is complete, at which point the upright position of #1 must be re-established.
Quote:
Originally Posted by Chronos View Post
I'd quibble that the driver doesn't usually notice the slight tilts in #1, and instead corrects for it through a combination of automatic human balance reflexes and automatic trail stabilization effects, but other than that, sure.

I think this is at least partially a disagreement on terms. Deliberate countersteering may not be occurring, even though some countersteer occurs through the same automatic balance reflex that we don't consciously track every wiggle of the handlebars, we just ride.

In order to lean, one must push against something - the bike seat and/or pedals. The bike then pushes against the ground. If the force is moving outside of the contact patch to the left, our reflexes will give the subconscious left twist of the handlebars, and then reverse the turn to follow the imbalance created by the lean.

Whereas to ride motorcycles, countersteering is much more pronounced and thus deliberate.
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  #44  
Old 02-21-2017, 12:28 PM
Quercus Quercus is offline
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Originally Posted by EdelweissPirate View Post
I understood Quercus to mean that there was no possible source of torque about the bicycle's axis of travel, not that there was no torque at the brake disc or the rear wheel. That said, I think turning from a steady-state travel is complicated enough without adding in acceleration or deceleration.
More precisely, looking at torque around the axis through the points where the tires contact the ground.


I don't think there's a lot of disagreement at this point is there? To turn left on a bicycle, there has to be a lean to the left (otherwise the rider falls over to the right when the front of the bicycle tracks left). That left lean can be produced through a temporary right turn of the handlebars ('countersteering') as part of the turn (typically not consciously noticed by the rider), or possibly an unsteered left lean caused by random bumps. And of course a combination of the two can also create a left lean (including a slight temporary overcorrection to a right lean).

Now, I'm not sure if at this point there's anyone who disagrees that countersteering happens (unconsciously or not) the vast majority of time someone turns on a bike.



But there's no fundamental difference between the dynamics of a motorcycle and bicycle. Motorcycles are heavier, probably a relatively lower center of gravity, and possibly a wider contact patch (but maybe not enough to make a difference given the greater weight), but the steering mechanisms are the same.
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  #45  
Old 02-21-2017, 12:52 PM
Chronos Chronos is offline
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Yes, a lean can be created by countersteering, but that's not the only way it can be created, and I maintain that it's not even the typical way that it's created on a bicycle.
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  #46  
Old 02-21-2017, 01:07 PM
Irishman Irishman is offline
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I guess the question is when you start to lean, how much sideways force is being reacted by the ground against the tires? Is it small enough to be swamped by the friction? Or is it merely the case that it isn't noticed because it falls into the intuitive corrections you are already making via your internal balance system?
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  #47  
Old 02-21-2017, 04:57 PM
EdelweissPirate EdelweissPirate is offline
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Originally Posted by Chronos View Post
Yes, a lean can be created by countersteering, but that's not the only way it can be created, and I maintain that it's not even the typical way that it's created on a bicycle.
Then what is the typical way to initiate a turn on a bicycle? You reject countersteering as a primary mechanism, but I haven't heard you offer an alternative.

What's your theory of two-wheeled vehicle dynamics, and why do you claim it's a more common way to initiate a turn than countersteering?
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  #48  
Old 02-21-2017, 06:55 PM
EdelweissPirate EdelweissPirate is offline
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Originally Posted by Chronos View Post
I maintain that it's not the currently-accepted theory, in that a theory must be well-tested, and so far as I can tell, this whole countersteering thing is barely tested at all.
Hm. I'd refer you to Vittore Cossalter's Motorcycle Dynamics for an articulation of the currently-accepted theory.

Section 8.3 (pages 345-350 of the English second edition) has what you're looking for.

Fajans wrote a very straightforward paper describing these phenomena:

J. Fajans, Steering in bicycles and motorcycles. Am. J.Phys,, 68:654, 2000

Specifically, Fajans asserts that there are only two ways to steer a bicycle or motorcycle: countersteering and hip-throwing. But hip-throwing is just hands-free countersteering; turning right requires hip-throwing to the left, which in turn rotates the front wheel to the left. Momentum then causes the rider to fall to the right, and the right turn is initiated.

You seem to be skeptical about whether the field of vehicle dynamics actually exists and whether people in that field have bothered to do any actual work. But if this work existed, it would be directly applicable to mechatronics and robotics, yes? It turns out that control theory from vehicle dynamics is directly applicable to how two-wheeled single-track robots steer. In other words, yes, through countersteering. I would argue that the application to two-wheeled robotics control constitutes a pretty good test of the theory that comes out of vehicle dynamics.

If there's some other mechanism that supersedes countersteering—the "typical way" bicycles turn, according to you—the robotics researchers are neither using it nor publishing papers about it. You have a real opportunity here to shake up the status quo. What's your theory?

Last edited by EdelweissPirate; 02-21-2017 at 06:58 PM.. Reason: Clarity and a typo
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  #49  
Old 02-21-2017, 09:01 PM
Chronos Chronos is offline
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I maintain that a bicyclist initiates a turn (say, to the left) by turning the handlebars counterclockwise and shifting his weight to lean to the left. And I've yet to see any refutation of that hypothesis, just absurdities like the claim that it's impossible to lean without countersteering.
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  #50  
Old 02-21-2017, 09:48 PM
scr4 scr4 is offline
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Quote:
Originally Posted by Chronos View Post
I maintain that a bicyclist initiates a turn (say, to the left) by turning the handlebars counterclockwise and shifting his weight to lean to the left. And I've yet to see any refutation of that hypothesis, just absurdities like the claim that it's impossible to lean without countersteering.
How do you think the "shift his weight to lean to the left" works? What exactly is supplying the external force to move his weight to the left?

Since we don't have movable fins or feathers, the only way to push yourself to the left is by applying force through the tires. But how do you push sideways againt the ground, through the tires? Do you think every time you turn, you are pushing sideways on your pedals to move your center of mass?
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