[python] Re: Stability Theory (Was: rubber pivot)


On Saturday, February 5, 2005, at 08:07 PM, Jürgen Mages wrote:

Olaf,

this theory might be an eye opener.
Peter was the first to tell me, that the riders postion towards
the bike is possibly more important than the frame geometry.


Yes, there is a chance that in this type of bikes rider's position is more crucial than on other bikes.


E.g. I am always stunned to see how much more stable P1 is
at high speed than P3, although the geometry is almost
identical.
Once I reached 70 km/h coasting downhill with P1.
Exactly the same hill I rode with P3 one year later and
had to start braking at 50 km/h, because I could not let it
go.


Perhaps you could compare your riding position on the two bikes by taking photographs from the side.



Would it be possible for you to illustrate your idea with a
drawing or by comparing two different pictures?


Actually I could hardly find any pic that is shot exactly from the side. I think this is necessary if the findings should be of any value.

Nevertheless I collected a few pics here:

http://www.liggcykel.se/pythonfolder/pythonangles.html



olaf




Regards from Jürgen.


Hi all,

Here is a vague theory on scientifically shaky grounds:

When comparing how difficult or easy different pythons are to ride we usually compare angles and measures of the bike itself without relating them to the rider. Important for the experience is perhaps also where and how the rider is placed on the bike.

I have looked through python pictures taken from the side with rider mounted. There aren't many, but enough to see that there are differences in where the pivot is situated in respect to rider's >> body.

When turning a python you use the lower part of your body, the movement begins where the thigh bones connect to pelvis, the rest of the upper body is static. The movement is circular and the centre of this circle is in the middle of your body. Now if the bike doesn't fold right below that centre it will become heavy and unstable to execute this movement, increasingly so the further away from the centre you get. You and the bike aren't aligned.

So perhaps, and here comes the theory, it is important for stability and balance that the pivot is placed below the centre of leg movement AND that the seat and pivot angle are aligned so when drawing a line from the pivot showing the extension of the pivot angle, it should continue upwards through the middle of the riders body.


olaf 

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