Posted by Charlie Gary on May 12, 2005, 2:24 pm
Nomen Nescio wrote:
> The physics of motorcyle dynamics has to be a complex subject being
> that one-track vehicles came on the scene quite late in human
> history. The modern bicycle predates the automobile by only a
> quarter century, or so.
> Marilyn Vos Savant and others have attempted to explain how a two
> wheeler stays upright and turns. See:
> http://www.wiskit.com/marilyn/bicycle.html
> My question is directed specificly to the aspect of rider position,
> as the physics has to be the same regardless of whether one sits in
> the usual way or hangs off to the side of the machine with is knee
> almost touching the roadway.
> When I want to make a turn, I push on the handle bar and shift my body
> weight to the opposite side. For example, if I want to turn right, I
> push on the right grip and my body moves to the LEFT while the
> machine takes a lean to the RIGHT. In essence, my body stays upright
> and essentially vertical to the roadway while the motorcycle assumes
> a lean underneath me. I think what happens is a push to the right
> turns the bar a little to the left. Gyroscopic precession then
> causes the bike to fall to the right a little and assume a circular
> path with the center approximately at the intersection of the
> extended centerlines of the front and rear axles. My body weight
> shift must be equal to its centrifigal force and is irrelevant to the
> motorcycle otherwise. This would explain the next paragraph.
> Racers however, appear to be hanging off their machines. Is there a
> good reason? Perhaps it has to do with the knee as a gauge as to how
> much lean the bike can stand before it slides out. Certainly there
> are no centrifigal forces felt by the rider as there are in a car,
> because the lean assumed by the motorcycle resolves all gravity and
> centrifigal forces vectorly to a point "down" with respect to the
> rider's senses. This is just like flying a coordinated turn in an
> airplane. You just get "heavier" but do not have a sensation of side
> force as you do in car. It also occurs to me that hanging off the
> bike cannot change its lean angle for a particular radius turn
> because the mechanics are the same: intersection of radii.
> Therefore it can make no difference in the resolved forces whether
> the rider sits upright during a turn or hangs off the bike. Am I
> correct? If so, the bike doesn't care, so there must be another
> reason why racers do what they do.
> Its interesting to note that when a motorcycle is at walking speed,
> it has to be manhandled and steered tiller-wise like a car, but once
> at any kind of stable speed, its "steering" is automatic as
> determined by little pushes and shifts of body weight as I described.
> Any attempt to turn the handle bar as you would a trike will
> immediately destabilize the bike as every rider knows. The reason
> why pushing on the handles is okay must be that simultaneously the
> body weight is shifted to the opposite side, maintaining balance.
> That makes it all the more difficult to explain why shifting the body
> off the bike on the side of the turn and lowering the knee to the
> pavement doesn't dump the machine.
Gravity pulls the bike toward the center of the turn.
Centrifugal force pushes the bike out.
Hanging in toward the center moves the center of gravity in and down,
allowing for a faster corner speed given the same lean angle.
And if you are really staying upright while your bike leans in the corner,
you're not doing yourself any favors. Lean with the bike, but keep your
head upright.
--
Later,
Charlie
Posted by The Family on May 12, 2005, 2:35 pm
Wow! this is pretty complex. Let's cut to the chase....
Assuming you ride a motorcycle, the next time you're out riding, find
an empty area of roadway, parking lot, etc. Something that allows
you to make some reasonably tight turns at a moderate speed.
Then, start a figure eight pattern, or something you are comfortable
with, at a slower speed. Gently increase the speed, trying not to
allow your torso to remain perpendicular to the surface(as you des-
cribed as upright), but leaning into the turn.
As you gain more confidence, and moderate speed, begin to lean
more heavily into the turns, even to the point where you are mildly
sliding off of the seat into the turn.
But, be very careful, the bike will want to fall into the turn. If your
speed in not adequate you may have problems. Just experiment
with the shifting of your weight into the turn a little.
When you begin to experience the sensation of the bike falling into
the turn, you will see the reason.
Thanks,
Gary
> The physics of motorcyle dynamics has to be a complex subject being that
> one-track vehicles came on the scene quite late in human history. The
> modern bicycle predates the automobile by only a quarter century, or so.
> Marilyn Vos Savant and others have attempted to explain how a two wheeler
> stays upright and turns. See:
> http://www.wiskit.com/marilyn/bicycle.html
> My question is directed specificly to the aspect of rider position, as the
> physics has to be the same regardless of whether one sits in the usual way
> or hangs off to the side of the machine with is knee almost touching the
> roadway.
> When I want to make a turn, I push on the handle bar and shift my body
> weight to the opposite side. For example, if I want to turn right, I push
> on the right grip and my body moves to the LEFT while the machine takes a
> lean to the RIGHT. In essence, my body stays upright and essentially
> vertical to the roadway while the motorcycle assumes a lean underneath me.
> I think what happens is a push to the right turns the bar a little to the
> left. Gyroscopic precession then causes the bike to fall to the right a
> little and assume a circular path with the center approximately at the
> intersection of the extended centerlines of the front and rear axles. My
> body weight shift must be equal to its centrifigal force and is irrelevant
> to the motorcycle otherwise. This would explain the next paragraph.
> Racers however, appear to be hanging off their machines. Is there a good
> reason? Perhaps it has to do with the knee as a gauge as to how much lean
> the bike can stand before it slides out. Certainly there are no
> centrifigal forces felt by the rider as there are in a car, because the
> lean assumed by the motorcycle resolves all gravity and centrifigal forces
> vectorly to a point "down" with respect to the rider's senses. This is
> just like flying a coordinated turn in an airplane. You just get
"heavier"
> but do not have a sensation of side force as you do in car. It also
occurs
> to me that hanging off the bike cannot change its lean angle for a
> particular radius turn because the mechanics are the same: intersection
of
> radii. Therefore it can make no difference in the resolved forces whether
> the rider sits upright during a turn or hangs off the bike. Am I correct?
> If so, the bike doesn't care, so there must be another reason why racers
do
> what they do.
> Its interesting to note that when a motorcycle is at walking speed, it has
> to be manhandled and steered tiller-wise like a car, but once at any kind
> of stable speed, its "steering" is automatic as determined by little
pushes
> and shifts of body weight as I described. Any attempt to turn the handle
> bar as you would a trike will immediately destabilize the bike as every
> rider knows. The reason why pushing on the handles is okay must be that
> simultaneously the body weight is shifted to the opposite side,
maintaining
> balance. That makes it all the more difficult to explain why shifting the
> body off the bike on the side of the turn and lowering the knee to the
> pavement doesn't dump the machine.
Posted by M. J. Freeman on May 12, 2005, 2:58 pm
rec.motorcycles.tech:
> Gravity pulls the bike toward the center of the turn.
And here I thought gravity pulled everything here on the surface
toward the center of the Earth.
Apparently gravity has a second job, running around to race tracks
and pulling riders laterally. Must be cutbacks in the pay given laws
of physics. And he's got all those little gravitons to feed, too.
> Centrifugal force pushes the bike out.
Centrifugal force doesn't exist. This is why clay pigeon throwers
stop their rotation with the arm parallel to the firing line and not
perpendicular to it.
> Hanging in toward the center moves the center of gravity in and
> down, allowing for a faster corner speed given the same lean
> angle.
Well, this at least is true.
--
Michael J. Freeman mike_freeman@SPMBLOKmac.com
'99 GSF1200S (The Evil Bandit) Cincinnati, OH, USA
"Insanity runs in the family... it practically gallops"
Posted by Charlie Gary on May 12, 2005, 4:10 pm
M. J. Freeman wrote:
> rec.motorcycles.tech:
>> Gravity pulls the bike toward the center of the turn.
> And here I thought gravity pulled everything here on the surface
> toward the center of the Earth.
OK, so my simplification eluded someone.
Gravity pulls the bike down to the ground, towards the center of the turn.
> Apparently gravity has a second job, running around to race tracks
> and pulling riders laterally. Must be cutbacks in the pay given laws
> of physics. And he's got all those little gravitons to feed, too.
>> Centrifugal force pushes the bike out.
> Centrifugal force doesn't exist. This is why clay pigeon throwers
> stop their rotation with the arm parallel to the firing line and not
> perpendicular to it.
Must teach different stuff in the science classes where I grew up.
>> Hanging in toward the center moves the center of gravity in and
>> down, allowing for a faster corner speed given the same lean
>> angle.
> Well, this at least is true.
Posted by M. J. Freeman on May 12, 2005, 5:56 pm
rec.motorcycles.tech:
> OK, so my simplification eluded someone.
> Gravity pulls the bike down to the ground, towards the center of
> the turn.
The center of the turn is in the ground? They keep moving these damn
tracks, don't they?
>> Centrifugal force doesn't exist. This is why clay pigeon
>> throwers stop their rotation with the arm parallel to the firing
>> line and not perpendicular to it.
>
> Must teach different stuff in the science classes where I grew up.
Different in this case meaning "bogus."
Check out this physical tutorial for kids, it should help you out:
http://www.glenbrook.k12.il.us/gbssci/phys/Class/circles/u6l1d.html
--
Michael J. Freeman mike_freeman@SPMBLOKmac.com
'99 GSF1200S (The Evil Bandit) Cincinnati, OH, USA
"Insanity runs in the family... it practically gallops"
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> that one-track vehicles came on the scene quite late in human
> history. The modern bicycle predates the automobile by only a
> quarter century, or so.
> Marilyn Vos Savant and others have attempted to explain how a two
> wheeler stays upright and turns. See:
> http://www.wiskit.com/marilyn/bicycle.html
> My question is directed specificly to the aspect of rider position,
> as the physics has to be the same regardless of whether one sits in
> the usual way or hangs off to the side of the machine with is knee
> almost touching the roadway.
> When I want to make a turn, I push on the handle bar and shift my body
> weight to the opposite side. For example, if I want to turn right, I
> push on the right grip and my body moves to the LEFT while the
> machine takes a lean to the RIGHT. In essence, my body stays upright
> and essentially vertical to the roadway while the motorcycle assumes
> a lean underneath me. I think what happens is a push to the right
> turns the bar a little to the left. Gyroscopic precession then
> causes the bike to fall to the right a little and assume a circular
> path with the center approximately at the intersection of the
> extended centerlines of the front and rear axles. My body weight
> shift must be equal to its centrifigal force and is irrelevant to the
> motorcycle otherwise. This would explain the next paragraph.
> Racers however, appear to be hanging off their machines. Is there a
> good reason? Perhaps it has to do with the knee as a gauge as to how
> much lean the bike can stand before it slides out. Certainly there
> are no centrifigal forces felt by the rider as there are in a car,
> because the lean assumed by the motorcycle resolves all gravity and
> centrifigal forces vectorly to a point "down" with respect to the
> rider's senses. This is just like flying a coordinated turn in an
> airplane. You just get "heavier" but do not have a sensation of side
> force as you do in car. It also occurs to me that hanging off the
> bike cannot change its lean angle for a particular radius turn
> because the mechanics are the same: intersection of radii.
> Therefore it can make no difference in the resolved forces whether
> the rider sits upright during a turn or hangs off the bike. Am I
> correct? If so, the bike doesn't care, so there must be another
> reason why racers do what they do.
> Its interesting to note that when a motorcycle is at walking speed,
> it has to be manhandled and steered tiller-wise like a car, but once
> at any kind of stable speed, its "steering" is automatic as
> determined by little pushes and shifts of body weight as I described.
> Any attempt to turn the handle bar as you would a trike will
> immediately destabilize the bike as every rider knows. The reason
> why pushing on the handles is okay must be that simultaneously the
> body weight is shifted to the opposite side, maintaining balance.
> That makes it all the more difficult to explain why shifting the body
> off the bike on the side of the turn and lowering the knee to the
> pavement doesn't dump the machine.