Hi, 
I am designing a special bicycle where the center of gravity is low
because  the rider is positioned near the ground, and between the two
wheels.
Can you explain to me how this affects stability and steering agility;
movement of the bodys center of gravity obviously plays a role here.

Hi Fredrikfen,

I believe that you have described what I have seen here in Aus. May I
ask where you reside?

My limited understanding of physics suggests that stability is gained
from a lower point of gravity. And that is exactly what you are
designing. The "bikes" I have seen shows the rider prostrate between
the forward and aft wheels, almost lying down. The other advantage of
this design is that any jolting bumps are absorbed via the suspension
attached to the wheels beyond the extremity of the rider's body. No
bone shaking jolts to endure. The bumps are encountered forward and
aft of the rider.

As for steering, I guess it would be the same as any bike. As long as
you have unhindered vision, the weight distribution should remain
constant.

I trust that our fellow physicists and mathematicians here can
enlighten both of us with correct formulas.

Please describe a bit more, as your idea is very interesting.

Phil

Thank you for quick response. I live in Norway,
The bicycle I am working with is supposed to be a "job-commuter", with
low wind drag and the posibillity to sit shielded from rain and snow.
Therefore the low profile. 

When riding a bike the rider constantly shifts his/her center of
gravity to nuteralize the force of gravity and centrifugal forces.
The ground is the reaction surface of the wheels right? so I guess
"the closer the rider is to the ground, the less body movement is
needed to adjust the vehicles of gravity? And the bike is less likely
to tip over in any direciton?

Vehicle stability is dependent on the the horizontal displacement of
the center of gravity to the pivot point of our bicycle.  If your
bicycle tips at 5 degrees and the center of gravity is high, the
offset is greater than if the center of gravity is low.  This is due
to the moment produced from the gravity acting on the center of
gravity.

Example:
Assume a bicyle with cg at 4 feet above tire contact with ground is
tilted 5 degrees: Offset from the center of gravity to the tire/road
reaction force is 4*tan 5=0.350 feet, or 4.2 inches.  The moment is
the weight of the system * this offset.
Now assume the different bicycle with the cg only 2 feet above center,
same tilt: 2*tan 5=0.175 feet, or 2.1 inches.  Assuming that the
system weight is the same, the moment is now cut in half for the same
amount of tilt.

In other words bicycle frame geometry is not as simple as it looks!
www.sheldonbrown.com is a good site for bicycle theory you can contact
Sheldon for more info.

I remember from patent law seminars I attended that the two areas that
get the most patent applications in the USA are bicycles and
toothbrushes. If you have hopes of patenting something new, please
check all applicable "current art" (the legal term for ANYTHING
ANYWHERE that describes what you propose).

My advice would be to hire a top-notch patent law lawyer to research
this for you before you commit any appreciable money or resources to
the project. It'd be a shame if your idea already existed in prior
art, even if it hasn't been developed. That'd mean you couldn't patent
the idea. You could manufacture it, of course--assuming it weren't
covered by a current patent--but so could anyone else.

G'luck,
dtc

Thank's, all of you!

Your comments were quite helpful.
bravedog; your answer was to-the-point, good!

As for patents, I think I may have something underways. I'll patent
here in Norway firstly (where law is simpler), and then I will
evaluate local production or selling the ideas to taiwanese, chinese,
or even american(?) bicycle manufacturers.

:)

- Fredrik -