[python] Re: TT prototyp riden

At 10:58 PM 2/26/2005 +0100, you wrote:
>the TT prototype attached in this mail I rode yesterday. It is terrible. The 
>forces on the front 
>wheel while pedaling are strong and I have to compensate them with the arms. 
>Without hands I can not ride it. 

This leads me to believe that one of the reasons the python is more ridable is 
the distance from the BB to the pivot.
a) On a python, the hips  act as an oscillation stabilizer. On the TT, it 
should be "stable" when coasting, but it would be more like riding with your 
feet on the handle bars. I've done that in my youth, but I won't now.
b) On a python, the hips are the steering point and each pedal stroke affects 
the steer less. The effect of each stroke on steering is 
~=arcsin((.5*crank_width)/BB_to_pivot) and increases rapidly as the distance 
shortens; if the pivot was closer to the BB, the steer force of each stroke 
would equal the pedal force!
c) The python's negative trail is an advantage; the weight of the body 
counteracts the pedal force as well. The wheel flop of positive trail in the TT 
case make turning the wheel by the feet easier.

>I wonder if moving the pivot to the front close to the bb and let the 
>pivot-angle go in the opposite 
>direction would help?

If the pivot was lined up with the BB, then your pedal force would affect it 
less, but it still would.

It would only really be saved by routing the chain to the rear wheel.

My 2c.
Ray

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