Bentley - Bike
Email - BentleyBeal@gmail.com
The reasoning behind the Flexbike design
When I began looking at bicycles with suspensions, I began to wonder
if it were possible to make such a bike in a much simpler and
First, it seemed to me that there were far too many tubes, plates
and welds in a typical bike frame design. It
makes a bike frame complicated and expensive to manufacture. Anyone
who has studied physics can spot the stress points in a typical bike
frame and recognize the need for strengthening. But, sometimes
greater strength can be achieved through flexibility and stress
Second, it seemed to me that there were far too many parts in the
front and rear suspension, too many bars, levers, cantilevers, coil
springs, pivots points, pins, shocks, etc. The shock
absorbing front forks also seemed to be incredibly heavy.
Designers were simply adapting a completely stiff bike frame to make
it flexible in selected places then compensating for the problems
this caused. Perhaps a better approach would be to
make some areas of a one piece pivotless molded frame flexible,
and other areas inflexible. That way the frame would be simpler
and cheaper to build, have fewer stress points, and not require so
much additional hardware to make it flexible.
Third, the bikes that were made of advanced materials were made
exactly like the bikes that were made out of ordinary metal,
except they cost at least five time as much. I thought, why not start all over again and design
something completely different taking advantage of the properties
of advanced materials not simply trying to adapt them to a
conventional bike frame design.
Could the bike be simple and easy to manufacture yet light
weight and inexpensive? Would it be possible
to make a frame out of advanced composite materials, comprised of
molded piece, stiff where it needed to be stiff and flexible where
it needed to be flexible? Could the
frame be designed to distribute the stress over the entire frame
rather than let it build up at critical points?
I sat down at my computer and designed a bike that I thought
would satisfy these design goals. During
the design process I also wanted to make the bike as ‘minimalist’
and ‘artistic’ as possible, not that I consider myself an artist. The drawing below is a crude rendering of
one of three different Flexbike designs, and is the prototype I am
working on now.
The Flexbike design
The experimental Flexbike prototype
bike project is based on a patented design for a bicycle that has
pivotless semi flexible molded frame. The
frame is designed to be formed from advanced composite materials
such as carbon fiber, but could be stamped out of light weight
flexible material or perhaps cast if a suitable material could be
found. The frame parts are not hollow
like pipe, but solid like a modern ski or archery bow. In the areas in the frame where
flexibility is required, the frame cross section is flat. In the adjacent areas where stiffness is
required, the cross section is coved or upside down U shaped. The material can also vary in width and
thickness from one area to another. The
section of the frame just behind the lower bracket is where the
bike is most flexible. It is important
to realize the frame is designed molded or stamped in one piece
and involves no welding. The
composite materials can be molded into the frame in layers with a
different directionality in each layer. Molded
pieces can be glued to other frame members that may be formed in a
different fashion, perhaps a stamped metal top frame section
joined to a molded carbon fiber bottom frame section.
The design does have stabilizers
that superficially look like typical shock absorbers. These stabilizers do not, however,
support the weight of the bike. They
are there only
for stabilization and oscillation dampening, and thus can be made
lighter than ordinary bike shocks. There
is also a stabilizer in both the front and the rear of the frame
in the design shown above. The struts are designed
with an adjustable resistance valve mechanism.
The front and rear wheel brackets
are removable using a secured quick release cam mechanism. That
means the front and real wheels can be removed as a unit, wheels,
breaks and all, so you can change the tires easily or perhaps
store the bike in a duffel bag or hang it on the wall in pieces.
It also allows the front wheel to be clamped on in different
places, thus lengthening or shortening the bikes trail. The trail
is what controls the bikes degree of quickness when making turns.
The bow shaped front frame, which supports the riders weight on
the front of the bike, is optional and could be replaced by a
conventional fork if you don't like the look of it.
The bow under the saddle helps support the riders weight on
the back of the bike. This bow can be
quickly and easily removed and replaced by a stiffer or more
flexible bow with a different contour to adjust for the riders
weight and different riding conditions.
The Flexbike main page is viewable at www.flexbikeusa.com and www.flexbike.us and www.flexbike.org