[python] Re: Jetstream

  • From: dirk.bonne@xxxxxxx
  • To: python@xxxxxxxxxxxxx
  • Date: Wed, 28 Feb 2007 13:25:26 +0100

Henry Thomas wrote:
> 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?
I used to believe that the neg trail must be as little as possible. I
relativate that a little now.

There is a borderline where the self centering force compensates the
"weight of front part + leg-feet weight (i.e. that what causes wheel
flop)".That is where the balance is.

On my python the trail is -140mm, and there is neither a noticeable flop
or noticeable self centering for small turning angles of the pivot. So
it happens that my python is very near to that border. Still, for larger
turning angles I can feel the front part going "uphill", and I need to
excert force to maintain that angle - i.e. self centering wins in the
end, I never experience wheel flop.

If you choose a larger neg trail this "going uphill" behavior is
obviously going to be larger.

Now, what is "best", I cannot say.

Speaking for myself, I definitely prefer the borderline area, where
there is only little force feedback when pedaling and/or steering.
Because I do not particularly like the python having a "strong will of
its own", like has been described by other pythonauts. But OTOH I
believe I could also get use to a large self centering force.

I guess a lot of it is due to what one is used to.

only adding to the confusion :-D

Dirk

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