Flexbike Information

Bentley - Bike Designer
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 cheaper way. 

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 redistribution. 

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.

US Patent Number 7,533,895

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