# [python] Re: [python]

• From: "dirk@xxxxxxxxxx" <dirk@xxxxxxxxxx>
• To: python@xxxxxxxxxxxxx
• Date: Fri, 20 Aug 2010 11:46:13 +0200 (CEST)

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Howard Stevens <hstevens94@xxxxxxxxx> hat am 20. August 2010 um 09:18
geschrieben:

> Hey Dirk!
>
> I made some modifications and it was most interesting. First I reduced the
> pivot angle to about 55degrees which reduced the PSI considerably and
> improved the ease of turning. Then I reduced it further to 50 degrees and
> the PSI ceased altogether! Hooray!! Also the steering was even easier and
> the wheel tilting was moderate...I would hardly call it wheel-flop at all.
> This is not what I expected...I thought that the less the pivot angle, the
> more difficult the steering would be, but it was easier! So it seems you
> have solved my problem! I think the geometry and mathematics of all this is
> not simple, for many factors come into play, and to varying extents on
> different cycles. As you said, the pivot angle was quite significant and so
> is the position of the pivot. I also suspect that the Cof G of the
> bike/trike is also important as the percentage of the total load on the
> front wheel and pivot would also affect the centreing forces and therefore
> the PSI. Perhaps bicycles and triicycles also behave differently...does
> anyone have any ideas on this?. I have about 35% of the weight on the front
> wheel and that seems ok even on steep ascents, but of course on gravel a
> steep ascent will lead to wheel slipping. I haven't found much problem with
> loading the trike, and suspect that it would make no difference at all, if
> it is placed directly over the rear axle.
>
hmmm. in that case, the lower angle combined with the different pivot placement
maybe means that the pivot axis meets your body roughly at the same place like
the normal configuration?

> In my particular case it seems that it was necessary to decrease the pivot
> angle to counteract the PSI induced by the forward position of the pivot.
> Perhaps it also counteracted a PSI tendency because only 35% of the weight
> is on the front wheel. Another possible factor could be the amount of
> negative trail with different pivot angles and wheel sizes. It is starting
> to sound a bit like rocket science!!!
> Cheers Howard
>
changing one thing changes everything. there is no perfect world, just a sweet
spot somewhere :-)

> Hi M Channon or is it McHannon!  Yes, your python pivot is pretty much where
> mine is, so it is interesting that you don't get PSI.  I'm not sure what PIS
> is....your not taking the piss outa me are you?  Cheers Howard

PSI (pedal steering interference) = PIS (pedal induce steering)

at some point we had a discussion about which of the two sounded better. we
agreed onto this:

http://en.openbike.org/wiki/PSI

regards,
DirkS
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