On low gears

On Sat, 7 Feb 2009 20:32:21 -0800 (PST), Frank Krygowski
wrote:

On Feb 7, 10:52*pm, wrote:

As for the bobbing and jiggling, the pedestrian walking next to the
~85 RPM rider looks enormously smoother to me.

Hmm. I see exactly the opposite. At 4:45 into the video, the ped's
head visibly moves up and down. It's quite obvious, comparing to the
white line with the black field under it just behind the ped. That
means the ped's body mass moves up and down, too. And unlike the
oscillating motion of the rider's legs, the energy isn't recoverable
in the crank mechanism.

Our brains normally tune out the up and down motion of walking, but
it's not hard to spot. When I walk side by side with my wife, her
shorter stride causes her to rise and fall with a different frequency
than I do. When I've looked at her face steadily while walking, I've
seen the "beat" phenomenon similar to that when tuning instruments -
out of phase motion, then in phase, then out of phase.

In any case, lifting and dropping anything a couple inches every
second eats energy. Doing it with well over 100 pounds of fat, muscle
and bone eats lots of energy.

- Frank Krygowski

Dear Frank,

I agree that we see opposite things. Are you saying that we raise and
lower our bodies "a couple of inches" with every step? That seems
extreme for the slight rise and fall on the flats, and implausible for
heading uphill.

Meanwhile, how much loss do you see in the rider's legs as they bend
and straighten far more than a pedestrian's legs?

The legs stop moving the instant the muscles stop contracting--there's
no flywheel effect on the reciprocating chunks of bone and muscle, and
it takes effort to bend and straighten them.

Again, the video, starting at about 4:50:
http://www.youtube.com/watch?v=FgIL6eHHgZU

A couple of inches of rise and fall? You may not be taking the camera
angle into account. Darned little downward component in the side view,
since he's going uphill--have a look around 6:30.

What about the continual erratic sideways back-and-forth hunting for
balance and the continual heaving on the handlebar? You can't see the
straining, but it's there.

Lose the special high seat, and things get even worse.

Cheers,

Carl Fogel

On Feb 8, 9:37*pm, wrote:

A common claim is that the rider is supported by the bicycle and
doesn't jiggle and bob as much as a pedestrian, so the bicycle must
still be more efficient.

That claim doesn't seem to be supported by this video:
http://www.youtube.com/watch?v=FgIL6eHHgZU

At ~4:50, a yellow-shirted pedestrian starts walking up Fargo Street
at ~48 RPM, next to a rider using ultra-low gearing at ~85 RPM.

At ~6:00, they reach the camera and can be seen from the side.

Even at a glance, the pedestrian looks smooth and relaxed compared to
the rider.

I think you're confusing "low frequency" with "relaxed." A man
climbing a ladder can look relaxed, too, but it's damned tiring after
a couple stories!

The rider's legs bend and straighten far more, knees rising much
higher, high-stepping. The pedestrian would have to goose-step or run
in place to match that inefficient motion, which again doesn't matter
at speeds on gentler slopes, where the bicycle's other advantages far
outweigh the losses.

I can't understand why you can't see the raising and lowering of the
pedestrian's mass in the video. That _must_ incur significant energy
waste.

Start the video again, at 4:30 where that same pedestrian's head is
aligned with the black and white object just left on our screen. The
ped's head - and therefore body - obviously rise and fall with each
step, as seen by comparison with that white "line," whatever it is.
The rider's head absolutely does not rise and fall anywhere near as
much.

At about 6:00, I can't possibly tell that the ped is "smoother" than
the cyclist, regarding motion of their trunks. Why? Because the
cameraman is bobbing so much that the picture's too unsteady!

Again, this is what I'm seeing. It seems to be opposite what you're
seeing. I don't know why, but it indicates we're not likely to agree
on other details.

And BTW, the up and down reciprocation of the rider's legs causes no
net change in potential energy, since one goes up as the other goes
down. And the interconnected cranks remove the necessity for
expending extra muscular work to change the leg's direction. That was
a shortcoming of treadle drive systems on things like the American
Star high-wheeler bike, one they share with uphill walkers.

IOW, that motion is not "inefficient."

- Frank Krygowski

On Sun, 08 Feb 2009 16:19:19 -0500, "(PeteCresswell)"
wrote:

Per :
Any details available about whether riders using ultra-low gears on
Fargo would climb the same hill faster or slower while simply pushing
the same bike?

That one's got me going.

Got a few pretty steep paved hills around here.

Also have a heart rate monitor embedded in my GPS.

Sounds like the only thing to do is a few climbs of a given hill
at a certain speed both ways - and record the heart rates each
way.

Dear Pete,

Whatever the results, I appreciate your effort!

With the right hill and gearing, the heart rates from your monitor,
and the time from one mark to another from a wris****ch, I think that
you'd be in business.

The hard part is finding a hill steep enough to reduce a rider to true
walking speeds.

I suppose that you could just handicap yourself by using gears that
yield a 1-to-1 ratio of pedal travel to tire travel and force creeping
speeds.

For what it's worth, a 20x38 with a 175 mm crank and a 2124 mm rear
tire produces a 1.017 overall ratio. If the tire is only 2090, you get
1.000 to 1.

I'd be fascinated to hear what happens with any gearing on a hill that
slows the bike something like 3~4 mph, even though that's mcuh faster
than this video's second run, starting at around 4:50 with 8.6"
gearing:
http://www.youtube.com/watch?v=FgIL6eHHgZU

The bike is moving at ~2 mph and has the equivalent of 0.624-to-1
gearing. That's roughly a 20x61 gear, so low that the pedal moves
noticeably farther than the tire.

Cheers,

Carl Fogel

On Sun, 8 Feb 2009 19:16:14 -0800 (PST), Frank Krygowski
wrote:

On Feb 8, 9:37*pm, wrote:

A common claim is that the rider is supported by the bicycle and
doesn't jiggle and bob as much as a pedestrian, so the bicycle must
still be more efficient.

That claim doesn't seem to be supported by this video:
http://www.youtube.com/watch?v=FgIL6eHHgZU

At ~4:50, a yellow-shirted pedestrian starts walking up Fargo Street
at ~48 RPM, next to a rider using ultra-low gearing at ~85 RPM.

At ~6:00, they reach the camera and can be seen from the side.

Even at a glance, the pedestrian looks smooth and relaxed compared to
the rider.

I think you're confusing "low frequency" with "relaxed." A man
climbing a ladder can look relaxed, too, but it's damned tiring after
a couple stories!

The rider's legs bend and straighten far more, knees rising much
higher, high-stepping. The pedestrian would have to goose-step or run
in place to match that inefficient motion, which again doesn't matter
at speeds on gentler slopes, where the bicycle's other advantages far
outweigh the losses.

I can't understand why you can't see the raising and lowering of the
pedestrian's mass in the video. That _must_ incur significant energy
waste.

Start the video again, at 4:30 where that same pedestrian's head is
aligned with the black and white object just left on our screen. The
ped's head - and therefore body - obviously rise and fall with each
step, as seen by comparison with that white "line," whatever it is.
The rider's head absolutely does not rise and fall anywhere near as
much.

At about 6:00, I can't possibly tell that the ped is "smoother" than
the cyclist, regarding motion of their trunks. Why? Because the
cameraman is bobbing so much that the picture's too unsteady!

Again, this is what I'm seeing. It seems to be opposite what you're
seeing. I don't know why, but it indicates we're not likely to agree
on other details.

And BTW, the up and down reciprocation of the rider's legs causes no
net change in potential energy, since one goes up as the other goes
down. And the interconnected cranks remove the necessity for
expending extra muscular work to change the leg's direction. That was
a shortcoming of treadle drive systems on things like the American
Star high-wheeler bike, one they share with uphill walkers.

IOW, that motion is not "inefficient."

- Frank Krygowski

Dear Frank,

We still see different things, so I'll leave that to anyone else to
pursue.

We also seem to be discussing different things about leg motion.

Bending and straightening legs is what I'm talking about. The more you
bend and straighten them, the more power is required, just as with the
sidewalls of tires.

Cheers,

Carl Fogel

On Feb 8, 7:37 pm, wrote:

I predict that when a hill is so steep that the pedal travels as far
as the tire, the bicyclist will be more efficient if he gets off and
pushes.

Time lost dismounting and remounting the bike means the pusher will
have to walk a bit faster than the rider to complete the steep climb
at the same time. This is theoretical to Carl but is well-known
practical issue for mountain bikers.

On Sat, 7 Feb 2009 20:32:21 -0800 (PST), Frank Krygowski
wrote:

On Feb 7, 10:52*pm, wrote:

As for the bobbing and jiggling, the pedestrian walking next to the
~85 RPM rider looks enormously smoother to me.

Hmm. I see exactly the opposite. At 4:45 into the video, the ped's
head visibly moves up and down. It's quite obvious, comparing to the
white line with the black field under it just behind the ped. That
means the ped's body mass moves up and down, too. And unlike the
oscillating motion of the rider's legs, the energy isn't recoverable
in the crank mechanism.

Our brains normally tune out the up and down motion of walking, but
it's not hard to spot. When I walk side by side with my wife, her
shorter stride causes her to rise and fall with a different frequency
than I do. When I've looked at her face steadily while walking, I've
seen the "beat" phenomenon similar to that when tuning instruments -
out of phase motion, then in phase, then out of phase.

In any case, lifting and dropping anything a couple inches every
second eats energy. Doing it with well over 100 pounds of fat, muscle
and bone eats lots of energy.

- Frank Krygowski

Dear Frank,

I'm not sure which theory this article supports (or neither or both),
but it may be worth a look:
http://www.pubmedcentral.nih.gov/art...?artid=2075334

The lazy devils didn't make the subjects walk up a 32% grade, much
less push a bicycle, but you and I are used to such wretched excuses
for proper research.

I'm not sure if I follow this first chart:

http://www.pubmedcentral.nih.gov/art...ure &id=fig01

But I _think_ that it's showing up-and-down movement (0.01 to 0.12
meters) for three gaits (normal, flat, and bouncy, averaged for the
six subjects (, at six speeds (1..6 km/h).

The flat gait (light grey triangles) stayed under 20 mm at all speeds.
(I think this was the gait where the subjects tried to minimize
bobbing.)

The normal gait (black circles) rose slightly with increased speed,
from ~10 mm to ~40 mm. (I think this was just walking normally.)

The bouncy gait (grey squares) drifted downward with increased speed,
from ~120 mm at 1 km/h to just under 80 mm at 6 km/h. (I think that
this was a deliberately exaggerated bobbing.)

(Of course, the bounce might be bigger going up a 32% grade.)

There are more charts about efficiency and speed and so forth.

Interesting conclusion:

"Thus, we were able to deduce that not only do humans move up and down
in normal walking to save energy via a pendulum-like mechanism
(Cavagna et al. 1976; Ortega & Farley, 2005) but also to make their
muscles work efficiently."

I hasten to add that the quote above doesn't mean that the efficiency
gained by moving up and down in normal walking is necesssarily more
efficient than sitting on a bicycle seat. But it does seem to run
counter to the common claim in these threads that it's inefficient.

Some posters familiar this kind of article might take a peek and
explain it further. An obvious enticement is the chance to point out
anything that I've misunderstood.

The whole study may be invalid for RBT because 5 of the 6 subjects
were women.

Cheers,

Carl Fogel

On 8 Feb, 17:04, Frank Krygowski wrote:

Now, ISTM that a major advantage of bicycling is that for extended
aerobic efforts, our muscles can put out more work (i.e. greater power
for a given time) if they operate in a mode of lower force, higher
contraction speed. *This is the reason racers don't pedal at 60 rpm.


Correct. High contraction forces limit blood flow so fatigue sets in
early. After about 4 to 6 minutes a positional change or gradient
reduction is required or a reduction of output power is encountered.
In the UK most of those 1 in4 or steeper are short enough to roll into
sitting, then stand, then sit, powering over the top from a standing
position. The decent then permits a full recovery to the vascular
system of the legs, as long as they are kept turning at a lessor load.

On Feb 8, 10:26*pm, wrote:
On Sun, 08 Feb 2009 16:19:19 -0500, "(PeteCresswell)"
wrote:

Per :
Any details available about whether riders using ultra-low gears on
Fargo would climb the same hill faster or slower while simply pushing
the same bike?

That one's got me going.

Got a few pretty steep paved hills around here.

Also have a heart rate monitor embedded in my GPS.

Sounds like the only thing to do is a few climbs of a given hill
at a certain speed both ways - and record the heart rates each
way.

Dear Pete,

Whatever the results, I appreciate your effort!

With the right hill and gearing, the heart rates from your monitor,
and the time from one mark to another from a wris****ch, I think that
you'd be in business.

The hard part is finding a hill steep enough to reduce a rider to true
walking speeds.

Of course, the test described doesn't really answer the question posed
at the top of the post.

To answer that question, you'd need an ultra-low-gear bike, and you'd
have to compare pedaling it and pushing it. I don't think anything
else would be conclusive.

- Frank Krygowski

On Feb 8, 10:32*pm, wrote:
On Sun, 8 Feb 2009 19:16:14 -0800 (PST), Frank Krygowski



wrote:
On Feb 8, 9:37*pm, wrote:

A common claim is that the rider is supported by the bicycle and
doesn't jiggle and bob as much as a pedestrian, so the bicycle must
still be more efficient.

That claim doesn't seem to be supported by this video:
*http://www.youtube.com/watch?v=FgIL6eHHgZU

At ~4:50, a yellow-shirted pedestrian starts walking up Fargo Street
at ~48 RPM, next to a rider using ultra-low gearing at ~85 RPM.

At ~6:00, they reach the camera and can be seen from the side.

Even at a glance, the pedestrian looks smooth and relaxed compared to
the rider.

I think you're confusing "low frequency" with "relaxed." *A man
climbing a ladder can look relaxed, too, but it's damned tiring after
a couple stories!

The rider's legs bend and straighten far more, knees rising much
higher, high-stepping. The pedestrian would have to goose-step or run
in place to match that inefficient motion, which again doesn't matter
at speeds on gentler slopes, where the bicycle's other advantages far
outweigh the losses.

I can't understand why you can't see the raising and lowering of the
pedestrian's mass in the video. *That _must_ incur significant energy
waste.

Start the video again, at 4:30 where that same pedestrian's head is
aligned with the black and white object just left on our screen. *The
ped's head - and therefore body - obviously rise and fall with each
step, as seen by comparison with that white "line," whatever it is.
The rider's head absolutely does not rise and fall anywhere near as
much.

At about 6:00, I can't possibly tell that the ped is "smoother" than
the cyclist, regarding motion of their trunks. *Why? *Because the
cameraman is bobbing so much that the picture's too unsteady!

Again, this is what I'm seeing. *It seems to be opposite what you're
seeing. *I don't know why, but it indicates we're not likely to agree
on other details.

And BTW, the up and down reciprocation of the rider's legs causes no
net change in potential energy, since one goes up as the other goes
down. *And the interconnected cranks remove the necessity for
expending extra muscular work to change the leg's direction. *That was
a shortcoming of treadle drive systems on things like the American
Star high-wheeler bike, one they share with uphill walkers.

IOW, that motion is not "inefficient."

- Frank Krygowski

Dear Frank,

We still see different things, so I'll leave that to anyone else to
pursue.

We also seem to be discussing different things about leg motion.

Bending and straightening legs is what I'm talking about. The more you
bend and straighten them, the more power is required, just as with the
sidewalls of tires.

You can't say "more power is required" if the forces are different!

Pedal forces are less than the rider's weight. Power is (essentially)
force times distance divided by time. And I think whether the power
produced is greater or less is close to the heart of our (so far)
inconclusive discussion...

.... although I'm afraid I've lost track of the precise question we're
trying to answer. I note that "faster" is different from "more
efficient," and "more efficient" is fairly meaningless for most
aerobically limited human effort.

What was the question, again?

- Frank Krygowski

In article
,
wrote:

On Feb 8, 7:37 pm, wrote:

I predict that when a hill is so steep that the pedal travels as far
as the tire, the bicyclist will be more efficient if he gets off and
pushes.

Time lost dismounting and remounting the bike means the pusher will
have to walk a bit faster than the rider to complete the steep climb
at the same time. This is theoretical to Carl but is well-known
practical issue for mountain bikers.

As a cyclocrosser, I would encourage you lazy mountain bikers to
practice dismounts and remounts

http://video.google.ca/videoplay?docid=4499489874611202316

Note footage of cyclocrossers carrying bicycles up stairs.

Also, at 3 minutes is some nauseating footage of riders traversing some
barriers on level ground. At 4:35 or so, a pair of riders, one after the
other, traverse a pit of pea gravel. The first rider (an experienced
MTBer and CXer) rides the pit, the second rider runs.

Hm. I should really re-upload some of that old video in higher quality.

--
Ryan Cousineau http://www.wiredcola.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing, we coach them."