balance

Dan who? said:

Excellent video but I am not convinced that gyroscopic effect is the
main source of stability at normal speeds. A bike will turn into a
lean even if it isn't moving. Hold a stationary bike by the seat
and lean it one way and the front wheel will turn into the lean.
This is because of the geometry of rake and offset which creates a
small moment about the steering axis. When walking a bike it is
easy to steer it this way while holding the seat. Gyroscopic effect
may help but it is not the primary factor at normal bicycle speeds.

If you ride no-hands, then try riding slowly and swing one knee
quickly from side to side. That causes gyroscopic steering, the same
as when leading a bicycle while walking, by holding only the saddle.
Quickly moving the saddle from side to side will just as quickly steer
the bicycle that way. That is not from trail and side load.

Jobst Brandt

Quoted message said:

Dan who?

It's Dan Merrick, though I don't think it matters.

Quoted message said:

Quoted message said:

Excellent video but I am not convinced that gyroscopic effect is the
main source of stability at normal speeds. A bike will turn into a
lean even if it isn't moving. Hold a stationary bike by the seat
and lean it one way and the front wheel will turn into the lean.
This is because of the geometry of rake and offset which creates a
small moment about the steering axis. When walking a bike it is
easy to steer it this way while holding the seat. Gyroscopic effect
may help but it is not the primary factor at normal bicycle speeds.

If you ride no-hands, then try riding slowly and swing one knee
quickly from side to side. That causes gyroscopic steering, the same
as when leading a bicycle while walking, by holding only the saddle.
Quickly moving the saddle from side to side will just as quickly steer
the bicycle that way. That is not from trail and side load.

Jobst Brandt

I have no doubt that I may be wrong but when you specify low speeds
doesn't that nearly eliminate gyroscopic effect?

Anyway, since my earlier post, I went down to the garage and spun the
front wheel of my bike both forward and then backwards while tipping the
whole bike to one side and then the other while keeping the steering
axis fairly plumb. (note that if I spun the wheel backwards and tilted
the bike, I could get a reverse steer) From this simple investigation it
seems that gyroscopic effect is significant but I also believe that the
lateral force/steering axis moment due to rake and offset as
demonstrated by tilting a stationary bike while holding the seat is
significant.

I also noted that if I held the bike fore-and-aft level and off the
ground, it would steer right if tipped right even if the wheel was not
turning.

It seems that there are at least three things working here:
Steering, rake, offset geometry moment
Gyroscopic moment
Static gravitational moment

There probably is no simple answer as to which is the primary influence
since it will depend on many variables such as speed, geometry, mass
distribution, phase of moon, etc.

In article
<[email hidden]>,

Ben C said:

Michael Press said:

In article
<[email hidden]>,

Ben C said:

On 2007-01-20, ddog <[email hidden]> wrote:
>
> david wrote:
>> > Can somebody please explain why a moving bicycle is easier to balance
>> > than a stationary one.
>
> Momentum is an additional force to keep you balanced.

Momentum isn't a force.

I will attempt to explain.

Momentum is the product of force and velocity.

Wrong.

I know, slip of the tongue etc. I meant to say "mass and velocity".

Quoted message said:

Remainder of the message has been excised for safety.

You are wise to take such precautions, but I think the remainder was
mostly all right.

There you go thinking again. The remainder is rife with
error. Did you read
David L. Johnson's reply?
<[email hidden]>

David did you the favor of reading it all and
commenting. What do you do? You do not reply to him, on
the points he raised. You do not thank him. You treat
him as if he never said anything.

--
Michael Press

On 2007-01-22, MkTm <[email hidden]> wrote:
[snip]

Quoted message said:

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics

wiki> Gyroscopic effects

wiki> The role of the gyroscopic effect in most bike designs is to help
wiki> steer the front wheel into the direction of a lean. This
wiki> phenomenon is called precession and the rate at which an object
wiki> precesses is inversely proportional to its rate of spin. The
wiki> slower a front wheel spins, the faster it will precess when the
wiki> bike leans, and visa-versa.

Isn't this the wrong way round? It's also "vice-versa" not "visa-versa".
The reference cited in the original article
(http://socrates.berkeley.edu/~fajans/pub/pdffiles/SteerBikeAJP.PDF)
says nothing of the kind (but is a good paper).

wiki> The rear wheel is prevented from precessing as the front wheel
wiki> does by friction of the tires on the ground, and so continues to
wiki> lean as though it were not spinning at all.

This sounds suspicious.

wiki> Hence gyroscopic forces do not provide any resistance to tipping.
wiki> At low forward speeds, the precession of the front wheel is too
wiki> quick, contributing to an uncontrolled bike's tendency to
wiki> oversteer, start to lean the other way and eventually oscillate
wiki> and fall over. At high forward speeds, the precession is usually
wiki> too slow, contributing to an uncontrolled bike's tendency to
wiki> understeer and eventually fall over without ever having reached
wiki> the upright position.

This sounds like rubbish. Gyroscopic forces would be higher at higher
forward speeds, surely?

On 2007-01-22, Michael Press <[email hidden]> wrote:
[snip]

Quoted message said:

There you go thinking again. The remainder is rife with
error. Did you read
David L. Johnson's reply?
<[email hidden]>

David did you the favor of reading it all and
commenting. What do you do? You do not reply to him, on
the points he raised.

I did reply to the points he raised! I don't know what you're talking
about.

The chief misunderstanding was in the interpretation of the word
"Impulse". I think we cleared that up OK, but if David L. Johnson or
yourself have any more useful comments to make then please go ahead and
make them.

Ben C said:

On 2007-01-22, MkTm <[email hidden]> wrote:
[snip]

Quoted message said:

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics

wiki> Gyroscopic effects

wiki> The role of the gyroscopic effect in most bike designs is to help
wiki> steer the front wheel into the direction of a lean. This
wiki> phenomenon is called precession and the rate at which an object
wiki> precesses is inversely proportional to its rate of spin. The
wiki> slower a front wheel spins, the faster it will precess when the
wiki> bike leans, and visa-versa.

Isn't this the wrong way round? It's also "vice-versa" not "visa-versa".
The reference cited in the original article
(http://socrates.berkeley.edu/~fajans/pub/pdffiles/SteerBikeAJP.PDF)
says nothing of the kind (but is a good paper).

wiki> The rear wheel is prevented from precessing as the front wheel
wiki> does by friction of the tires on the ground, and so continues to
wiki> lean as though it were not spinning at all.

This sounds suspicious.

wiki> Hence gyroscopic forces do not provide any resistance to tipping.
wiki> At low forward speeds, the precession of the front wheel is too
wiki> quick, contributing to an uncontrolled bike's tendency to
wiki> oversteer, start to lean the other way and eventually oscillate
wiki> and fall over. At high forward speeds, the precession is usually
wiki> too slow, contributing to an uncontrolled bike's tendency to
wiki> understeer and eventually fall over without ever having reached
wiki> the upright position.

This sounds like rubbish. Gyroscopic forces would be higher at higher
forward speeds, surely?

http://en.wikipedia.org/wiki/Precession

The period of precession is inversely related to the period of spin.

Dan who? said:

Quoted message said:

Quoted message said:

Excellent video but I am not convinced that gyroscopic effect is
the main source of stability at normal speeds. A bike will turn
into a lean even if it isn't moving. Hold a stationary bike by
the seat and lean it one way and the front wheel will turn into
the lean. This is because of the geometry of rake and offset
which creates a small moment about the steering axis. When
walking a bike it is easy to steer it this way while holding the
seat. Gyroscopic effect may help but it is not the primary factor
at normal bicycle speeds.

Quoted message said:

Quoted message said:

If you ride no-hands, then try riding slowly and swing one knee
quickly from side to side. That causes gyroscopic steering, the
same as when leading a bicycle while walking, by holding only the
saddle. Quickly moving the saddle from side to side will just as
quickly steer the bicycle that way. That is not from trail and
side load.

Quoted message said:

I have no doubt that I may be wrong but when you specify low speeds
doesn't that nearly eliminate gyroscopic effect?

.... just DO IT! If you can't ride no-hands, take your front wheel out
and spin it in your hands. Even at low speeds it will respond when
its rotational axis is changed.

If you hang it from a string attached to one end of the axle and spin
the wheel, you'll notice another effect. The wheel will precess about
the vertical axis inversely to the speed of wheel spin. That is, as
it slows its spin its rotation about the vertical axis (steering)
speeds up. This is a clue to why lean steer works at low speeds.

Quoted message said:

Anyway, since my earlier post, I went down to the garage and spun
the front wheel of my bike both forward and then backwards while
tipping the whole bike to one side and then the other while keeping
the steering axis fairly plumb. (note that if I spun the wheel
backwards and tilted the bike, I could get a reverse steer) From
this simple investigation it seems that gyroscopic effect is
significant but I also believe that the lateral force/steering axis
moment due to rake and offset as demonstrated by tilting a
stationary bike while holding the seat is significant.

I think that has been explained in other posts.

Quoted message said:

I also noted that if I held the bike fore-and-aft level and off the
ground, it would steer right if tipped right even if the wheel was
not turning.

There are two effects that have been explained. Don't confuse them
all over again.

Quoted message said:

It seems that there are at least three things working here:
Steering, rake, offset geometry moment
Gyroscopic moment
Static gravitational moment

Merge that into two effects.

Quoted message said:

There probably is no simple answer as to which is the primary
influence since it will depend on many variables such as speed,
geometry, mass distribution, phase of moon, etc.

For practical folks who do these things it is simple. For example.
walk your bicycle holding it by the saddle and notice which way it
steers when leaned statically and when moving, noting where gravity
is. When moving in a curve and leaning a bicycle adds curvilinear
acceleration go gravity so "down" is a different direction than when
standing. I suspect that is where the complexity lies for some
observers.

The excellent video of stunt riding that Carl Fogel posted:

http://www.glumbert.com/media/bikerobatics

demonstrates that clearly.

Jobst Brandt

In article <[email hidden]>,

Ben C said:

On 2007-01-22, MkTm <[email hidden]> wrote: [snip]

Quoted message said:

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics

wiki> Gyroscopic effects

wiki> The role of the gyroscopic effect in most bike designs is to
help wiki> steer the front wheel into the direction of a lean. This
wiki> phenomenon is called precession and the rate at which an
object wiki> precesses is inversely proportional to its rate of
spin. The wiki> slower a front wheel spins, the faster it will
precess when the wiki> bike leans, and visa-versa.

Isn't this the wrong way round? It's also "vice-versa" not
"visa-versa". The reference cited in the original article
(http://socrates.berkeley.edu/~fajans/pub/pdffiles/SteerBikeAJP.PDF)
says nothing of the kind (but is a good paper).

wiki> The rear wheel is prevented from precessing as the front wheel
wiki> does by friction of the tires on the ground, and so continues
to wiki> lean as though it were not spinning at all.

This sounds suspicious.

wiki> Hence gyroscopic forces do not provide any resistance to
tipping. wiki> At low forward speeds, the precession of the front
wheel is too wiki> quick, contributing to an uncontrolled bike's
tendency to wiki> oversteer, start to lean the other way and
eventually oscillate wiki> and fall over. At high forward speeds,
the precession is usually wiki> too slow, contributing to an
uncontrolled bike's tendency to wiki> understeer and eventually fall
over without ever having reached wiki> the upright position.

This sounds like rubbish. Gyroscopic forces would be higher at higher
forward speeds, surely?

Gyroscopic forces just don't play much of role in keeping a bike
upright. That's been shown empirically. Time to move on.

Peter Cole said:

Ben C wrote:

[snip]

Quoted message said:

Quoted message said:

wiki> Hence gyroscopic forces do not provide any resistance to tipping.
wiki> At low forward speeds, the precession of the front wheel is too
wiki> quick, contributing to an uncontrolled bike's tendency to
wiki> oversteer, start to lean the other way and eventually oscillate
wiki> and fall over. At high forward speeds, the precession is usually
wiki> too slow, contributing to an uncontrolled bike's tendency to
wiki> understeer and eventually fall over without ever having reached
wiki> the upright position.

This sounds like rubbish. Gyroscopic forces would be higher at higher
forward speeds, surely?

http://en.wikipedia.org/wiki/Precession

The period of precession is inversely related to the period of spin.

You're right, thanks for that, that is what the Wikipedia article is
talking about.

"don Gabacho" (clip) By itself, a bicycle can still not balance itself.
^^^^^^^^^^^^^^^^^^^
Do you recall that the OP asked about the difference between balancing a
moving bike and a stationary bike? The bungee cord put the bike in motion,
and after that was out of the picture. It did NOT supply any balancing
corrections.

Boiling down all that has been said: Leaning the bike provides steering
corrections. A rolling bike responds to these steering corrections better
than a stationary bike. Hence, as a bike starts to fall, the feedback that
counters the fall is greater at higher speeds.

Quoted message said:

Dan who?

Answered in previous post

Quoted message said:

There are two effects that have been explained. Don't confuse them
all over again.

OK

Quoted message said:

Quoted message said:

It seems that there are at least three things working here:
Steering, rake, offset geometry moment
Gyroscopic moment
Static gravitational moment

Merge that into two effects.

OK

Quoted message said:

Jobst Brandt

MkTm said:

The Wiki article I linked to earlier had a link to a video of a
riderless bike coasting along seemingly without a care and even able to
take some abuse along the way.

"Seemingly" is the key word.

Obviously there are mechanisms, not merely bikes, which can be designed
to enhance
balance and its duration. Just the same there is no bike that can
balance itself any more than it can upright itself---just as there is
no watch that can mark time eternally much less start itself.

Thank you everbody for your thoughts.

david said:

Can somebody please explain why a moving bicycle is easier to balance
than a stationary one.

david said:

Thank you everbody for your thoughts.

So do you know now?

Quoted message said:

david said:

Can somebody please explain why a moving bicycle is easier to balance
than a stationary one.

David L. Johnson said:

Absent Husband said:

david said:

Can somebody please explain why a moving bicycle is easier to balance
than a stationary one.

Maybe you can work this out for yourself!!

Think about - what is the difference between a moving bike and a
stationary one (ie. what two big round things are doing something
different in each case??). That might start you on the right track,
yes?? 😉

If you're going to make snide remarks, it's better to be right. There has
been considerable discussion about the gyroscopic effect of the wheels,
but the bottom line is that that is not what allows you to balance on a
bike. People have designed bikes with counter-rotating wheels to cancel
the gyroscopic effect, and the bike is still ridable. You can also
balance quite well while barely moving, in which case there is essentially
no gyroscopic effect. Lots of us can balance on a bike while it is not
moving forward at all (called a track stand). Actually, that practice
shows what we really do, in that you can't do a track stand without the
front wheel being turned at a significant angle. Then, pushing forward on
the pedals tilts the bike to one side, pushing back (on a fixed gear)
tilts it to the other. You do the same thing while riding by turning the
wheel slightly and/or leaning -- you don't even notice it, usually.

People often ride bikes several hours without falling or stopping. If
you do not believe that the centrifugal force from the rotating wheels
helps to keep you upright then I suggest you try to trackstand for a
couple of hours with your feet off the ground.

Believe your physics if you want, but I'd prefer to believe mine.

EJ in NJ

On 2007-01-23, Ernie Willson <[email hidden]> wrote:
[snip]

Quoted message said:

People often ride bikes several hours without falling or stopping. If
you do not believe that the centrifugal force from the rotating wheels
helps to keep you upright then I suggest you try to trackstand for a
couple of hours with your feet off the ground.

Believe your physics if you want, but I'd prefer to believe mine.

The fact that balancing on a moving bike is easier than trackstanding
doesn't imply that gyroscopic forces are involved.

Leaning a forwards-moving bike left makes it turn left but turning left
makes it lean back to the right (centrifugal force), tending to correct
the left lean. This provides a degree of stability, which is enough to
keep the bike upright in conjunction with rider input.

All this would work if the wheels were replaced with skis or equipped
with counter-rotating flywheels.

As someone (A.Muzi I think) pointed out, it's not trivial. The big
unknown IMO is exactly what the rider does, since it's unconscious.

Ernie Willson said:

Quoted message said:

Quoted message said:

> Can somebody please explain why a moving bicycle is easier to
> balance than a stationary one.

Quoted message said:

Quoted message said:

Quoted message said:

Maybe you can work this out for yourself!!

Quoted message said:

Quoted message said:

Quoted message said:

Think about - what is the difference between a moving bike and a
stationary one (ie. what two big round things are doing something
different in each case). That might start you on the right track,
yes?

Quoted message said:

Quoted message said:

If you're going to make snide remarks, it's better to be right.
There has been considerable discussion about the gyroscopic effect
of the wheels, but the bottom line is that that is not what allows
you to balance on a bike. People have designed bikes with
counter-rotating wheels to cancel the gyroscopic effect, and the
bike is still ridable. You can also balance quite well while
barely moving, in which case there is essentially no gyroscopic
effect. Lots of us can balance on a bike while it is not moving
forward at all (called a track stand). Actually, that practice
shows what we really do, in that you can't do a track stand without
the front wheel being turned at a significant angle. Then, pushing
forward on the pedals tilts the bike to one side, pushing back (on
a fixed gear) tilts it to the other. You do the same thing while
riding by turning the wheel slightly and/or leaning -- you don't
even notice it, usually.

Quoted message said:

People often ride bikes several hours without falling or
stopping. If you do not believe that the centrifugal force from the
rotating wheels helps to keep you upright then I suggest you try to
trackstand for a couple of hours with your feet off the ground.

Quoted message said:

Believe your physics if you want, but I'd prefer to believe mine.

I take it you jut joined this discussion because you seem to have
missed what keeps a bicycle upright. If all else fails, you might
look at:

http://www.sheldonbrown.com/brandt/gyro.html

Jobst Brandt

Try this:

Replace your skewer with something longer that you can easily hold on to
both ends of, then have a friend spin your wheel. It doesn't even have
to be very fast to feel significant effects. While the wheel is
spinning, try to tilt your hands from side to side. After doing this I
doubt you'll argue any more that gyroscopic effects make it
significantly easier to stay balanced.

Kevin

Ben C said:

On 2007-01-23, Ernie Willson <[email hidden]> wrote:
[snip]

Quoted message said:

People often ride bikes several hours without falling or stopping. If
you do not believe that the centrifugal force from the rotating wheels
helps to keep you upright then I suggest you try to trackstand for a
couple of hours with your feet off the ground.

Believe your physics if you want, but I'd prefer to believe mine.

The fact that balancing on a moving bike is easier than trackstanding
doesn't imply that gyroscopic forces are involved.

Leaning a forwards-moving bike left makes it turn left but turning left
makes it lean back to the right (centrifugal force), tending to correct
the left lean. This provides a degree of stability, which is enough to
keep the bike upright in conjunction with rider input.

All this would work if the wheels were replaced with skis or equipped
with counter-rotating flywheels.

As someone (A.Muzi I think) pointed out, it's not trivial. The big
unknown IMO is exactly what the rider does, since it's unconscious.

In article <[email hidden]>, [email hidden] says...

Quoted message said:

David L. Johnson said:

Absent Husband said:

david wrote:
> Can somebody please explain why a moving bicycle is easier to balance
> than a stationary one.
Maybe you can work this out for yourself!!

Think about - what is the difference between a moving bike and a
stationary one (ie. what two big round things are doing something
different in each case??). That might start you on the right track,
yes?? 😉

If you're going to make snide remarks, it's better to be right. There has
been considerable discussion about the gyroscopic effect of the wheels,
but the bottom line is that that is not what allows you to balance on a
bike. People have designed bikes with counter-rotating wheels to cancel
the gyroscopic effect, and the bike is still ridable. You can also
balance quite well while barely moving, in which case there is essentially
no gyroscopic effect. Lots of us can balance on a bike while it is not
moving forward at all (called a track stand). Actually, that practice
shows what we really do, in that you can't do a track stand without the
front wheel being turned at a significant angle. Then, pushing forward on
the pedals tilts the bike to one side, pushing back (on a fixed gear)
tilts it to the other. You do the same thing while riding by turning the
wheel slightly and/or leaning -- you don't even notice it, usually.

People often ride bikes several hours without falling or stopping. If
you do not believe that the centrifugal force from the rotating wheels
helps to keep you upright then I suggest you try to trackstand for a
couple of hours with your feet off the ground.

Believe your physics if you want, but I'd prefer to believe mine.

And it is also much easier to balance on one roller-blade when moving than when standing still. Would you also argue
that this effect results from the gyroscopic effect of those tiny little wheels?

Mike

Quoted message said:

Quoted message said:

It seems that there are at least three things working here:
Steering, rake, offset geometry moment
Gyroscopic moment
Static gravitational moment

Merge that into two effects.

Quoted message said:

Jobst Brandt

Dear Jobst,

I see on this page:
http://www.sheldonbrown.com/brandt/gyro.html
That you wrote:

There are three effects that interact when walking the bicycle, hand on
saddle only. They are:
1) Gravitational force of leaning, bearing on the trail of the wheel.
2) Inertial force of the center of mass of the wheel and handlebar
acting on steering when the bicycle is rapidly tilted.
3) Gyroscopic moment about the inclined axis of the fork when the frame
is tilted about its horizontal long axis.

These are the three effects that I had in mind although I may not have
stated them very clearly. So, is it two or three?