| Pivot Angle [°]
|| Trail [cm]
|| Seat Height [cm]
|| BB-Seat Diff. [cm]
|| Ground Clearance [cm]
|| Wheelbase [cm]
|| Weight [kg]
|| BB-FWA [cm]
|| BB-EOS [cm]
|| Turning Circle [m]
|| Front Tubing [mm]
|| Wheel Size [inch]
|| CG [%]
|| 25.4x12.5 braced
|| 26" 26"
I started on this python 2 years after seeing Jurgen Mages' from scratch. Impossible to resist. My construction philosophy was to follow instructions as much as possible. Other than some of the materials I followed Jurgen Mages' design as closely as I could, so the end product is as close as I could get to a P3.
My background is not particularly technical, but I have had odd jobs that involved whacking things with hammers and welding. I have also done light machining of parts, but who has a milling machine in their garage? This project is appealing because all you need is basic hand tools, spme patience, and a cheap wirefeed welder. a lot of bicycle projects are intimidating because they require special machining, dipping stuff in high temp brine baths, vacuum bagging (lots of fun!) etc. Of course one could build a SuPeR python with all of this, but one can also build a really good bike without it. That is the appeal of this design.
I searched high and low on the internet for 10mm x 40mm steel tube for months, never located any. Finally settled on 1" x .25" x .065" 4130 steel tube from Aircraft Spruce for the front fork. Since it is much less wide than the 40mm wide tube suggested I also braced it with seat stays from a donor bike, also 4130 steel. So far it works. I have crashed many times (on my grass proving ground at the park) with no damage to the front, even when my shoe got stuck in there somehow.
Here is where I had to change the design. all I had available was a donor bike frame (my old commuter)of 4130 round steel tubing. But I wanted to use the same suspension as on the P3. I welded steel unistrut sections(from Home depot to the round tube to make flat vertical sides similar to square tube. Then welded a 3/16" steel plate to the bottom of the unistrut section to hold the rubber block shock absorber. It works! I hope to tidy up this part of the design on the next one.
I had an extra long steel mountain bike fork (heavy!) from the donor bike and that became the back end. I reinforced fork with another tube over the steerer tube, round tube again. I don't know if this is necessary or not but was trying to stay close to the design I welded steel plate to the sides where it contacted the unistrut to create the same bearing-surface-with-brass-plates that the P3 uses and it seems to be doing OK. there is room for panniers there, later after I'm through crashing in the park...
Rear derailleur is an older Shimano Deore, front is Shimano tiagra. The crank is Shimano tiagra triple (50-40-30) and the pedals are spd clipless mountain bike pedal, all from JensonUSA. I used bar end shifters (dura-ace on sale) and Bike Nashbar jailbreak levers (in my parts bin). Brake and derailleur cables are Jaguar, also from Jenson USA (I live on an island so I do a lot of internet shopping). the front brake is an Avid Disc brake (cable type) and the rear is a Cane Creek center pull type, which seems to be almost completely useless since the rear end of the bike is so light. Good to have a disc brake up front where all the stopping power is found because of the weight distribution.
wheels and tires
26" front and rear, street type, not knobbly mountain style. Font is 1.5" wide, rear is 1.4".
8/15/10 First Ride
with video and photo ops ( that's my son Kenji in the photo, me in the video). More like crab-walking than riding really, 12 falls in an hour, no injuries thanks to grass field proving ground (between Keiki soccer practice). Wondering if I may have built it upside down?
Ok, after riding several laps with both hands trailing on the ground over 2 hours, it seems like a long haul. Fell about 4 times. It is just like learning to ride all over again, no credit at all for 30+ years of experience.
I lowered the back rest a bit because it was digging into my shoulder blades (from my constant flailing about). went back and read Jurgen's account of learning to ride...apparently I'm right on track.
One lap ( 1/4mile?) without falling or putting hands down! Of course I'm still flailing my arms all over the place but, baby steps.
Many laps, able to semi-confidently put hands on the under seat brake/shifter handles. an actual in flight fall recovery! Amazing watching my body work this out. It has alsmost nothing to do with conscious thought, just keep riding till the body figures it out, and try to stay out of it's way.
But it feels OK, almost normal and getting more so. Totally lost it on the hill though...
I added a handlebar, the "moustache" type bolted to the front section just in front of the pivot. it helps me feel stabile a little but does not really steer. The brakes are in a better position and the bar end shifters are right at my fingertips so that is nice. Tried a steering damper and abandoned it, not useful. Riding around the neighborhood is better now,I have graduated from the grass soccer field. Still not ready for cars, panicky moments still happening. Some really great turns, almost graceful!
Modifications! I chopped the bike in half and cut out 2 sections then re-welded. This is the only bike I know of that still stands up when cut in half! I cut about 8 inches from the length of the bike and increased the pivot angle very slightly. Best I can measure it is now about 65 degrees. Also welded in bolt-ons for the fenders. The ride is improved significantly with the increased pivot angle and the turning radius is better. All in all more maneuverable and also better stability. It's comfortable now. I can see myself riding to work with this bike. Weight is up there (18.5kg, 40.8 lbs.) but in line with the P3 so not too bad.