From: martin@adpgate.UUCP (Martin Golding)
Newsgroups: rec.motorcycles
Subject: Re: Countersteering a shafty
Date: 18 Aug 92 22:01:23 GMT
Article-I.D.: adpplz.1497
Organization: ADP Dealer Services R&D, Portland, OR


> ... [David said] you simply need to push on the gas tank with your knee
> to make the bike steer. This doesn't sound like counter-steering at all.

skao@booboo.tcs.com (Simon Kao) writes:
> To which I say: Yes, it is, but it's hidden from the user. That is to
> say, if you use your left knee to push against the tank, in order to
> balance yourself, you will unconciously lessen your push on the left
> handlebar, which is equivalent to pushing the right handlebar, which 
> results in countersteering to instigate a turn to the right.

To which I reply,

God, what an incredible heaping pile of bullshit that damned Dana dug up.
(Oh what a stink we generate, when we set out to excavate.)
I _still_ think he (it's HE, isn't it?) has too much time on his hands,
and thinks it's funny. Which it isn"t, yet, but it's getting closer.


Since I (and anybody on a bicycle, and most skilled people on the right
motorcycles) can steer with _no_ hands, shifting body weight obviously
works independently of countersteering.

If anybody thinks that hands-free steering is impossible on their particular
motorcycle, I'll be glad to demonstrate it for them. Particularly if they
have early model Ducati 900SS's, on which it may take me weeks to develope
my skills.

If anyone is not convinced that weight shifts affect direction, I refer
them to "swervies" from my post "games you can play on your motorcycle".


So, here's some physics:

In order to turn the motorcycle without falling over, you have to lean.
Like any other vehicle, the force acting on its center of mass must, when
projected, fall within a polygon bounded by the areas of support. On a
motorcycle, this is two or three inches across on a line between the wheels,
so you have to lean the bike against the centrifugal force when you steer.

Since your motorcycle is gyroscopically stabilized, forcing it to lean
will produce a near equivalent turn. (On my BMW, which has very little
righting force, I need no additional input once the turn has started. On
my Virago, which forces itself out of turns, I have to maintain the input
to maintain the turn. I suspect, without evidence, that motorcycles
which force themselves _in_ to a turn are undesirable.)

Your angle of lean can be established by adjusting the system's center of
mass by shifting your weight, or by adjusting the position of the area
of support by countersteering. (This moves the wheels out from underneath
the center of mass.) Either or both mechanisms are effective; your preference
will depend on total mass, your mass, leverage (handlebar length), your
personal riding experience and training, and all kinds of magical stuff
related to the front suspension, which are well beyond my understanding.

That with the total force acting on the center of mass projecting into the
area of support while leaned over the bike will actually _turn_ is either due
to the front wheel stabilizing some small angle displaced from the plane of
the rear wheel, or to the net sales of ice cream cones in your area. The
latter possibility would explain the reduced use of motorcycles in winter.


Martin Golding    | My opinions, mine, mine mine oh what the heck...
Dod #0236         |  here, you have them too.
[motcsd!]mcspdx!adpgate!martin
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