Hello all, After seeing Juergen's great site and hearing from Dirk, I started doing some looking into the math of bike stability with the intent of building a Python. I bought some extra tubes I needed, so now on to design. After some research, I programmed a small bit which gives the self-stable speed range (if any) of an idealized bike (fixed weight, ridden no-hands, thin "metal" wheels). The effect of real tires would depend on the pivot trail and angle, and I hope to do that at some point. For large trail, it is negligible. For small trail, the offset of the contact patch changes the effective steering angle as the bike leans. It appears, so far, that a few factors definitely allow a self-stable python. The most important is small-ish negative trail, no more than -4cm. A longer wheelbase, with rear mass CG more forward, a more horizontal pivot angle and several others can add stability. I'll try to compile it soon so others can try it out. I noted that the "height" of the pivot is not the real factor, it is the angle and trail it creates. Actually, steeper angles -with the same trail- give a wider stable speed range. Think of the pivot moving up around the wheel until it approaches that of a Flevo. It appears that if the pivot was directly in front of one's crotch (!) it would add self-stability, but as it got higher up it would seem to make leg-steering awkward. It does seem to be the large angle which gives the straightening "feel" users report, but it is the large negative trail which makes them unable to roll by themselves. With an angle of ~45deg. and ~4cm trail, a python should roll on its own around 4m/s. Of course, inherently unstable bikes are ridable, it is just the amount of learning and attention required. I'm still working on the script and understanding the meanings of the stability matrix equations, hopefully I'll be able to contribute something more concrete soon. I want to use the seat from my old recumbent trike, which fit well, I just need to make up my mind about the final geometry. Cheers, Ray Schumacher http://rjs.org ============================================================ This is the Python Mailinglist at freelists.org Listmaster: Juergen Mages jmages@xxxxxx ============================================================