[python] Re: [python]
- From: Dirk Bonné <dirk.bonne@xxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Fri, 20 Aug 2010 11:14:15 +0200
Hello Howard,
I am very glad to hear that! Amazing how fast you are able to change
pivot angles on your bike. I had pivot problems myself on the pythoon,
and it took me weeks of grinding theeths to make a change.
May be if the pivot angle gets decreased, the axis line gets better
positioned? Anyway,have some photos/some geonmetry numbers to look at?
So we can see what happened to the bike?
About wheel-flop (or the opposite: self centering): I always found that
smallest self centering effect is best. It should just be large enough
to counteract wheel flop. It should be so that the front part does not
want to tend to turn into the curve more than it does. That way you get
a very agile bike where everything is in balance. On the "pythoon," this
balance is tipped toward self-centering (more centering than flop).
Still okay but not as good as it has been on the "baby python". On the
"baby python" even sharp-turning was practically effortless (except for
slow-ultra-short-turns where the front part is swung to its max
deflection), making it quick in reacting - I had only to overcome the
inertia of the front part. It was ideal to swing through these stupid
bars I meet on bicycle roads.
On the flevo (positve trail), without the rubber damper installed, you
had wheel flop when turning into the curve, you had to stop it from
turning, and pull the front part up again. And that is because there is
no self centering to compensate the wheel flop. But it was still (well)
rideable, and damn quick in the curves, slower to get out of it again ;-)
I have no idea if trikes and bicycles are different.We have none that
tried 50 or 55 degrees on a 2wheel-python yet, afaik.
Dirk
On 20.08.2010 09:18, Howard Stevens wrote:
>
> 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.
>
> 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
>
> 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
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