[python] Re: Jetstream

Sometimes a little ignorance is bliss.  When I made the three pythons, I
wasn't worried about trail at all.  My three concerns were seat height,
pivot angle and BB location.  The BB location was indirectly located by:
a) making sure it was far enough from the front axle so it didn't cause
severe chain angles and auto-gear changing issues
b) making sure that the rider could actually reach the pedals due to the 26"
wheel size, so the BB was slowly raised and rotated back, which again
indirectly set the pivot angle.
c) and lastly, due to prior experience, I know that too high of a BB is not
comfortable or efficient.  This was self-remedied later by the fact that I
had to raise the seat.

I try to to over-think a bent, especially a radical one like a python.  The
easiest thing for me is to roughly duplicate the efoort of another, do a few
changes that I understand, and then see if I can figure out how it works.
Everything ends up being a compromise with something else.  I think there is
more than enough understanding for anyone to buid a completely rideable and
enjoyable python, BUT, after learning to ride it, then you have to decide
how you like to ride it, and if you find it lacking, what you need to change
to make it more what you want.  Few will ever have a "perfect" python,
especially someone like me with more . . . "spirited" riding preferences.  I
have learned to accept a bent as it is, and learn to adapt to it and then
try to get skilled enough to push it to it's maximum ability, and see if I'm
happy there.  If so, great, if not, I'll built another slightly modded, or
move on and build something else.  Cool thing about bents, and specifically
the python, is very basic mods can produce a very different riding
experience.

I tracked down as many ice racing movies as I could and put them all here:
http://www.youtube.com/group/iceracers
In the "Brantford Ice Races 2005", Marcel is shown a couple times on his
python, plus there is a couple shots of me on the tilting python delta.


| Ghislain Pillet wrote:
| > Hello Henry,
| > Congratulations for yours extensive works and the way you're unfolding
| > them to us !
|
| Its not quite there yet, but getting closer every weekend :-)
|
| > Looking at your JetStream design, as a python rider I'm puzzled about
| > the amount of negative trail induced by the distance between the pivot
| > and the fwd wheel ; the recommendation on the list being to try to
| > reduce it to the minimum.
|
| Well I guess I based it on the specs for 25hz PC2 which has a 10"
| -trail, and his riding report
| http://www.freelists.org/archives/python/10-2005/msg00017.html, put now
| that you bring it up, he does have a much larger front wheel, so I guess
| this is something that I missed when reading through the forum archives.
| Reading Dirk's notes I guess I thought bigger negative tail was better,
| so I thought I would ask the group: Is the smallest negative trail the
best?
|
| > About JetTrike, may I suggest you to not bury too quickly your
| > speculoos drive version, it should remind you what stability means.
|
| I am actually really struggling with this. I think the 100mm positive
| trail may not be enough. So I have been doing some research into trail,
| and plotting the results for comparison. I looked up the table in
| Bicycle Science and they seem to place it somewhere between 1/2 or 1/3
| across from zero to the intersection with the axle (see attached). Using
| these ratios, it would appear that the 100mm +trail with 57.5 pivot
| angle of the Speculoos is too far for the 504 wheel radius. Maybe 55mm
| or less would be better.
|
| Does anyone have any experience or suggestions.
|
| > As we, Python riders, know that going downill on Python, at speed,
| > (for me it is over 40km/h), is adventuring in unstable world where
| > Python can get definitely very lunatic, even on empty road with nice
| > surface, with no beam wind at all, and a totally relaxed mood !
|
| I haven't given up on the Speculoos version just yet, but I am pulling
| my hair out in exasperation. The trail is all wrong, maybe too much, it
| flops from side to side and upsets the rear balance.
|
| By contrast, it would appear that the python self-correcting would
| center and thus balance the trike with much less hassle, but maybe the
| grass just seems a bit greener over in that pasture right now.

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