From: lotto@laura.harvard.edu (Jerry Lotto)
Newsgroups: rec.motorcycles
Subject: Re: Countersteering a shafty
Date: 2 Sep 92 13:14:38 GMT
Organization: Chemistry Dept., Harvard University
In-reply-to: john@kennel.FIDONET.ORG's message of 31 Aug 92 22:14:52 GMT

>>>>> On 31 Aug 92 22:14:52 GMT, john@kennel.FIDONET.ORG (John Hamilton) said:
John> Monday August 31 1992 13:46, Paul Cantrell wrote to All:
PC> I think John is a little confused here. He's confusing countersteering
PC> with how the front wheel acts during a turn. Countersteering is when you

John> John is not confused.

No, John, you were just unclear.  Your article (the one Paul replied
to) certainly implied that the front wheel would be prevented from
turning in EITHER direction.  Actually, camber thrust would cause a
leaned motorcycle with a straight front wheel to turn.  In fact, rake
and trail can be selected so that this is the "optimal" steering
geometry.  On the other hand, that motorcycle would be inherently
unstable - you would have to work pretty hard to ride it in a straight
line.

John> And vice versa. Get someone to videotape you in a turn at onset of
John> counter-steer, slow it down on replay, and you will see for yourself.

That also depends on the magnitude of the countersteer.  If you are
negotiating a sweeper at speed and initiate the lean with a
countersteer, the deflection of the front wheel never preceeds the
lean.  In other words, you cannot see the countersteer front wheel
deflection.  The most aggressive countersteer deflection is only about
3 degrees.  The amount of lean (which will determine the turn radius)
is a function of the DURATION of a countersteer.  The cs MAGNITUDE
determines the rate of lean.

John> My only point was that the writer I responded to claimed a turn could be
John> made without countersteer. The only practical test would be to eliminate
John> the wheel's ability to turn past zero degrees to the opposite direction
John> of the intended turn

No, there are plenty of practical tests.  The one utilized in the
Photographic Analysis of Motorcycle Operator Control Responses
involved a light-weight "dial" extension off of the triple tree and a
vertically mounted movie camera to measure actual front wheel
deflection.  Since nothing was blocking the steering head, magnitude
and duration of the countersteer could both be measured on
photographic analysis.

BTW, the approach you suggest would be highly impractical because the
front wheel steering hub has to move about a degree in either
direction to accomodate weight shifts and surface imperfections.  That
degree is sufficient to countersteer.

John> are symmetrical). I contend that a practical turn of 90 degrees at 40 mph
John> cannot be made without countersteer at least once on entry to the turn.

You kind of stack the deck here, n'est pas?  If you call a turn which
is too sharp to make without countersteering "practical", you are then
right by definition.  It is also a function of the steering geometry
and motorcycle weight distribution.  Results would differ on a
GoldWing or a CB125TT trainer.  In either case, it certainly possible
to lean the motorcycle without an initial countersteer.  It just isn't
as efficient.

John> I still am looking for someone who claims otherwise to volunteer to have
John> a block put on their fork to stop countersteer (at least, any that would
John> cross zero degrees) and be filmed negotiating the test curve. :-)

The original film from the PA is probably still available from NPRSI
if you are interested.  The summary report is probably a lot cheaper
and is readily available from the Motorcycle Safety Foundation.  MSF
Instructors should all have their own personal copies.
--
Jerry Lotto <lotto@lhasa.harvard.edu>      "Have you hugged the curves today?"
Chemistry Dept., Harvard Univ.              MSFCI, HOGSSC, BCSO, AMA, DoD #18
Newsgroups: rec.motorcycles