On Oct 23, 8:54 pm, wrote:
Joseph Santaniello writes:
A while ago there was a thread discussing no-handed riding and the
role gyroscopic forces play in bike turning.
I hypothesized that gyroscopic forces were not that important, and
several things were pointed out to me that almost convinced me. A
good dose of insomnia allowed me to think about this for several
hours and I am now convinced that gyroscopic forces are virtually
irrelevant for riding bikes, hands or no-hands.
It was postulated that a clown-bike with tiny wheel would be
difficult to ride no hands due to the small gyroscopic forces.
Since I don't have a clown-bike to play with, this remains a
mystery. But I have observed little kids riding small wheel (10")
bikes at below walking pace. I have also spun some 12" wheels in my
hand a various speeds to feel what sort of gyroscopic forces are
there. Not much. A little kid with a sense of balance not as
developed as an adult can ride one of these bikes. I do not believe
a kid could keep one of these bikes upright by manual correction
alone. These small bikes are stable by themselves, and since the
gyroscopic forces are so low, there must be something else at work
here. This isn't proof or anything, this is just what got me
thinking.

You should have seen the demo at InterBike where an engineer built a
front wheel with a forward rotating flywheel (brass disk) between
the spokes driven by a small motor at about the speed you expect from
a 27" wheel at 10-15mph. He rode this bicycle no-hands at below 2mph,
steady as a rock, up and down the isles. Without the flywheel
turning independently, the bicycle was as difficult to ride no-hands
as any other bicycle with wheels that size.

That sounds like fun! That seems to indicate that the gyroscopic
forces counter the "flop" tendency and keep a bike from turing too
much. I wonder if his gizmo would make a chopper bike rideable no
hands...


I finally pulled out a big plywood board (much to the chagrin of my
wife who imagines there are myriad things I could be better spending
my time on) and propped it up at an angle and put a bike on it to
simulate what happens when a bike is in a turn. It was suggested
that in a turn a pendulum hung from the top-tube would hang parallel
to the seat tube. When riding no hands in a constant radius turn,
this cannot be the case, and I suspect that it is not the case with
hands on the bars either. Experiments with my plywood board show
that when force is applied straight down through the bike the
steering remains straight no matter what the angle of the board
(simulated angle of lean). In a turn, the steering cannot be
straight, otherwise it wouldn't be called a turn, it would be called
a crash. So in a turn (a no-handed one in particular) something has
to be holding the steering at a non-straight angle. The only thing
it can be is that the center of mass is moved to the side of the
plane that is the centerline of the bike. This makes the steering
flop into the turn. The combined force of gravity and the
acceleration of the turn act from the center of mass through the
contact patches of the tires. Since the center of mass is not in
the plane of the bike's centerline, this means that the combined
force is not parallel to the seat tube and thus a pendulum hanging
from the top- tube could not be parallel with the seat tube. Riding
with hands on the bars I suspect is the same. But a rider could
force the bike to be in the same plane, but then they would need to
hold the steering at the proper angle manually. This would no doubt
require quite a bit of skill, and I believe in practice to be
virtually impossible. But perhaps it is just this skill which
separates the good from the great.

Please discover why one should use paragraphs. You must have come
across this in school.

Who says I went to school? Ok, I'll try. ;-)


So what does all that mean? It means that "flop" from an off-center
center of mass is what makes a bike turn, and thus while gyroscopic
forces make help the initial turn of the steering due to induced
lean, it is an unnecessary component that is ultimately irrelevant
to turning a bike.
The whole COM argument was brought about by thinking about how a
radio controlled motorcycle I used to have worked.

I think your research came up with the wrong result.

An easily repeatable exercise of coasting down a smooth road at more
than 20mph riding no-hands, is to shake one knee from side to side
while resting the other one against the top tube for stability. I
think there is where you will see the effect the best. In addition,
shimmy on a bicycle cannot occur without gyroscopic forces of the
front wheel.

I did that very same exercise today on my ride while I was polishing
my theory. I don't argue that gyroscopic forces do not turn the
steering from leaning the bike. I argue that the steering would turn
anyway even if the gyroscopic forces were not there, and that the same
force that would do this turning is the force that holds a bike with
no hands in a constant arc turn.

Joseph