--On Friday, November 1, 2002 9:15 AM -0500 Kevin Hawkins
<[EMAIL PROTECTED]> wrote:
That's right, there's no such thing as body steering. Now, don't tell that
to all of the road racers out there.
Actually, what's perceived as body steering is actually displacing your
weight to one side of the motorcycle which effectively changes the Center
of Gravity (CG). This change in CG affects the amount/type of inputs
required at the bar to achieve "the turn".
Now, what about peg pressure to help lever the bike over? :^) Inside
pressure, outside pressure?
I've heard all of these arguments and all of Keith's stuff, although I've
not ridden the no BS bike.
I cannot agree with Keith. My evidence is: when riding my motorcycle, I set
the trottle lock on a stretch of roadway. I then took my hands off of the
bars altogether. I was able to, with some agressive peg wieghting and body
english, cause the bike to travel back and forth in the lane. Further, I
was able to get it to go into a shallow turn.
Now, I doubt I could have made it corner worth a damn, that requires inputs
from the steering head. My test proves that body steering DOES have an
effect, however minor, on motorcycle control. The effects of body steering
are so weak compaired to handlebar inputs, that it appears to be
non-existant.
The deal with Keith's no BS bike is psychological, in part. Since you have
your hands on handle bars, which don't work, it blows all your reflexes and
mental state. Thus you conclude that the bike simply cannot be moved
without use of the bars.
Now, for all you safety guys who are right now hitting reply to tell me how
dangerous my test was, bugger off. It's my damn life. :-)
Any of you ride bicycles as a kid? Ever ride 'no hands'? Could you steer
the bike?
There isn't any difference between a bicycle's steering and a motorcycle's
steering in terms of basic function. The difference comes in magnitude.
Motorcycles are bigger and heavier and travel much faster. The heavier
wheels spinning faster creates considerably more gyroscopic stability. This
stability makes it harder to cause the bike to destabilise. You have to
destabilise the bike to get it to turn. By destabilise, I mean you move the
center of gravity out away from the line that passes through the contact
patches of the two wheels. When that happens, a resultant force is created
which causes the bike to fall in that direction. The front wheel and
steering assembly deflect as a result of that fall and cause the bike to
begin to swerve in that direction. Eventually, either the bike regains
stability by moving the contact patches back below the center of gravity or
the bike swerves tighter and tigheter until it crashes.
When we steer by handlebars, we are pushing directly on the contact patch.
When you countersteer, you push the contact patch out from under the
center of gravity (COG) causing the bike to fall in the opposite direction.
Then, the bike begins to swerve in that direction, deflecting the front
wheel into the fall. When we pull out of the turn, we push the contact
patch back under the COG thus stabilizing the bike which goes straight.
When we steer by body language, we are moving the COG out from over the
contact patch. It is the same mechanism, but the work needed to move the
COG far enough to make a significant deflection is considerably greater
than the work needed to move the contact patch out from under the COG.
Gyroscopic forces in the spinning wheels fights the displacement of the COG
(and the contact patch, for that matter). With body steering, you have a
much less powerful tool to overcome the inherent stabilty of the moving
bike. With the handlebars, being connected directly to the axel of the
front wheel, you have a very powerful tool to overcome the stability.
Thusly:
1) Body steering becomes less effective as speed (and mass of the wheels)
increases.
2) Handlebar steering becomes less effective at speed, but it is so
powerful you dont' notice it. At speed, due to the forces at work, a
smaller displacement is needed for the same turn. However, greater force on
the bars is needed to effect that displacement. It kinda all comes out in
the wash.
The bicycle is a great tool for learning motorcycle dynamics. Since it is
so much lighter, one can test priciples at lower speeds. Ride a bicycle
through a puddle at a great enough speed to require countersteering. Right
after the puddle, countersteer agressivly and look at the tracks left on
the pavement. You will see the front wheel track displace to the outside of
the turn (moving the contact patch from underneath the COG), then it will
pass through the rear wheel path to the inside of the turn (the bike
falling and the front wheel deflecting to 'catch' the bike). It will stay
to the inside until the you pull the bike out of the turn at which point it
will be on the outside of the new turn until stability is reached.
So, in practice, Keith is right. Body steering is so weak as to be nearly
useless at high speed. But to say that it has no effect or is impossible is
false. I would wager that I could make the no BS bike swerve back and forth
with body steering alone. Can I ride the twisties with body steering only?
No. Does body steering have an effect? Certainly. In fact, the fact that it
is so weak compared to handlebar steering can be used to great effect to
'fine tune' one's lean angle.
Now, here is a fun trick to learn a bit more about this stuff. Take a soda
straw or something like that and tape it to the steering head of your bike
in such a manner as it forms a pointer to a ruler or guage of some sort
taped to the tank (or glove box [obligatory GTS content]). Ride in a safe
manner! Watch the position of hte pointer as you manuver the bike around.
The deflections of the pointer are not always what you would expect.
If you countersteer a bike and block the handlebars from swinging back the
other way to swerve, it would fall right now. Whee!
I'm done now, but boy to I feel better for getting that off of my chest.
Take care,
Mike
--
Michael Weaver (706)542-6462 [EMAIL PROTECTED]
Engineering Services EITS
University of Georgia, Athens Ga. )O(
Public PGP key: http://www.arches.uga.edu/~weaver/pgp.html
