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Re: [Phys-l] Bicycle question



The website I referenced earlier has a section under bicycle science
called "counter-intuitive." It agrees with some others writing on this
thread that motorcycle riders might first turn the handlebars in the
opposite direction they want in order to make the quickest turn. The
site I referenced implies this is also true of bicycles.

I am a bicycle commuter and have ridden a bicycle to work for about 35
years. I had to experiment with this, and this afternoon as I rode back
to work from lunch I made some observations. Note, below I separate
"leaning" from "steering." When I say "steer" I mean turn the
handlebars. When I say "lean" I mean shift my body position. Here's
what I found...

(1) When preparing for a turn, it is natural to begin leaning before you
begin steering. This is actually required. If you steer before you
lean then you initially end up turning the wrong direction and you have
to correct. I had not thought this through, and until today I did not
realize how much earlier I lean before I steer. Check it out, you
always begin to lean significantly before you begin to steer.

(2) Notice that I said "when preparing for a turn." Here I want to
emphasize "preparing" because that means there is some time involved.
Sudden emergency turns are a problem because you don't have the required
preparation time. An emergency turn in the shortest time is going to
require a non-intuitive maneuver.

(3) Notice that if you steer first (as you might do in an emergency) and
you steer away from the danger, this really eats-up precious avoidance
time because you initially go the wrong direction (toward the obstacle)
and then you have to correct and recover. Even if you don't throw
yourself directly into the obstacle you may subsequently hit the
obstacle because you wasted time with the wrong maneuver.

(4) Thus, even at slow speeds on a bicycle (in contrast to a motorcycle)
a good emergency maneuver seems to be an initial quick (but slight)
steer into the danger. I experimented with this and it seems absolutely
true, even at low speeds, but I also need a lot more riding experience
before I would be any good at this maneuver. If I do not lean, but do a
sudden (but slight) steer in the direction I don't want to go (i.e.
toward the obstacle), the bike *suddenly* leans in the correct direction
to avoid the obstacle. Once the lean has been forced, I immediately
compensate by reversing the steering to the direction I want to go. I
believe this process makes the desired turn more quickly because the
initial backwards (counter-intuitive) steering sets up the correct lean
much, much quicker than I could have accomplished without the
counter-intuitive steering. In addition to the need to train yourself
to do this, you also need to practice the recovery because my
inexperience at this procedure causes me to wobble more, and if it were
truly an emergency at 15 mph I might lose control due to my
inexperience.

So I am going to practice this some more to see if I can develop a
better emergency turning procedure that begins with a steer toward the
danger.

Here again is the website, and also a quotation from that site. The
quotation is about motorcycles, but it is in a section about bicycles,
and it seems absolutely true for my bicycle moving at slow speeds (5 to
15 mph).


* * * quotation from
http://www.losethetrainingwheels.org/default.aspx?Lev=2&ID=36 * * *


The significance of the bicycle's non-minimum phase behavior is that the
bicycle usually does the opposite of what the intuitive mind would and
might expect. As an example, if we want to steer right using handlebar
actions as opposed to leaning, we actually steer first in the opposite
direction, or to the left. Accident studies show that nontrivial numbers
of motorcycle deaths occur in the case of less experienced riders - as
when an obstacle or danger appears, the intuitive reaction is to steer
away. But, in doing so the motorcycle sets up a lean towards the
obstacle and the motorcycle invariantly impacts the object - and hence a
serious collision results.

The proper emergency steering action is called "counter-steering,"
whereby the skilled rider initiates a turn by turning towards the
hazard. This action sets up a lean away from the hazard, and thus the
rider can thereafter quickly and safely turn away from the hazard as a
proper lean has been established. In addition, skilled motorcyclists
will combine this action with an upper torso lean away from the hazard,
in that sense "intuitive," so as to as efficiently as possible extricate
themselves from the hazardous circumstance.

* * * end quote * * *


Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu