[python] Re: wheel flop vs pedaling induced steering
- From: Dirk Steuwer <dirk@xxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Tue, 8 Jan 2008 21:06:55 +0100
Am Samstag 05 Januar 2008 20:03:26 schrieb Jürgen Mages:
> Hi Dirk,
>
> > Had some time to study the PX.5 pictures. btw: should this one -
> > http://www.flickr.com/photos/python_uploads/2073763738/ - be named
> > PX.5 as well?
>
> That is the PX.4 and it had a lower steering pivot angle than the PX.5.
> The PX.4 was not rideable due to excessive wheel flop.
>
> > So you cleverly moved the seat forward, while having the drivers back
> > still leaning against the rear part of the bike. So it is in essence
> > a normal python with increased trail and b>>a-distance Do you think,
> > this is somewhat related to the position of the hip joint in front of
> > the pivot, as on of your pictures suggests? Or isit related to the
> > added weight of the front part, because it is longer?
>
> The PX.5 was rideable but felt awquard. I blamed it on the PSI-effect
> because it felt like PSI, but it could also have been wheel flop: I
> remember that pushing this bike was pretty difficult.
>
Theory:
The more b>>a, the less PSI. I presume the force of the cyclist onto the pedal
is the starting point of this effect.
But, the seat get the resulting force on the opposing side (diagonally
across), reducing PSI.
In the case of the PX.5 however, the Seat is on the pivot, reducing this
leaver to zero, so no corrective force here.
Also, if b>>a, the front part - in case of the px.5 - is longer, since "b" is
done by extending the frame. This adds more wheight and gives the CoG of the
front a longer leaver to create Wheel Flop. Also, the bigger the wheels, the
higher the CoG of the front, and the bigger is the Wheel Flop Effect.
So this leaves us in a race condition, where we cannot optimise one thing,
without worsening the other...
If a python has smaller wheels, b>a can be optimised with a frame, no longer
than that needed for bigger wheels anyway. Also, the CoG of the front part
should be lower, putting less force into the WF effect.
Is there evidence that small-wheeled pythons suffer from less P/SI and WF?
Do they allow for more tolerance in pivot angle choice, bevore WF and P/SI
effects start to occur?
Hec, i wish i could test a few different designs to get a better feel for
this :-)
BTW: I uploaded a first graphic related to this discussion:
http://en.openbike.org/wiki/Pedal/Steering_Interference
Somehow, the picture got lost during the domain transfer...will see..
Regards,
Dirk
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