Re: On low gears

On Sat, 7 Feb 2009 20:32:21 -0800 (PST), Frank Krygowski
<frkrygow@xxxxxxxxx> wrote:

On Feb 7, 10:52 pm, carlfo...@xxxxxxxxxxx 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
.

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