[python] Re: PC2 rideable - and test results
- From: "Sam v. Herwaarden" <sammelweis@xxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Sat, 8 Oct 2005 16:38:44 -0400
But a flatter angle does result in a larger turning circle, right? I
would personally find that quite important (though downhill stability
is, of course, a plus as well).
It's really very good that a research like this is done now - good to
know before I start building (long waiting period isn't all downsides
;)). None of the results actually really surprise me though, they all
make sense - the thing I'm really curious about is whether new tests
will actually confirm Dirk's calculations, that there is one most
stable point around 55 degrees after which stability starts to
decline.
I'm starting to doubt about the planned head angle for my carbon
python - I had in mind 68, but seeing these results, combined with the
idea that a carbon front fork is really light (at least it should be)
and I barely fit around the wheel with my legs (short fork) I think
something close to 60 might be better.
Sam
BTW, Jurgen, what does the python site favicon (browser title icon),
the swallow, stand for? ;) I only just noticed it.
On 10/8/05, Jürgen Mages <jmages@xxxxxx> wrote:
> Great tests - thanks a lot Tim.
>
> Low angles were preferred by all test riders. Some blind
> tests would have been interesting too, as you mentioned.
> But I think the direction is clear.
>
> The plot that Dirk made some time ago shows a maximum
> seat rising effect at angles around 53 deg.
>
> http://www.python-lowracer.de/pics/height_vs_aa.gif
>
> This means that the centering force is maximized.
>
> So the rule of thumb for python frame building might be:
>
> Get the pivot angle as low as possible. Try to reach the
> angle with max. seat rising. If wheel flop shows up then
> go higher with the angle until it disappears.
>
> As I have experienced with the PX.4 (pivot 55 deg) this can
> be tricky:
>
> The 55 angle felt very nice and tight turns were possible. But I had
> to adjust the bike for my inseam lenght. So I welded another BB
> right in front of the old one to get some 10 cm more.
>
> http://www.python-lowracer.de/modifications.html
>
> This was fatal, because the additional weight caused the front
> wheel to flop and I felt like sitting on a seesaw. So I had to
> incrementally rise the pivot angle until the wheel flop disappeared.
> This happened EXACTLY at 63 deg.
>
> So one has to consider both angle and weight of the front part.
> If you build the front part as light as possible then you can
> use lower pivot angles.
>
> Cheers,
> Jürgen.
>
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--
Waarom rijden er zo veel fietsers in auto's rond?
// Loesje
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