I want to forward this posting from Ghislain. The attached pdf was too big for the freelists restrictions. I changed the image into a small jpg (hope you don´t mind Ghislain).
Here is his posting:
Hi All, Why a 20" Python ? Dirk proved it could be made. Other personal reasons : smaller diameter of wheel, compared to 26", - makes easier the fixing of the bottom bracket shell; tubes instead of flats can be used. - more adjustment made possible for various length of legs, ok for a child 14 years old, or long legged adult, as I am. Moving the seat aft up to 10cms from its more forward position, gives a different feeling, while the beast remain ridable. - overall dimensions less cumbersome, easier to put in the car and overall weight reduced compared 26" - apart from 61or 64 teeth ring for the crankset, all parts can be found easily.( I found, cheap second hand, a flawless 61 teeth ring.)
Why did we lower the seat height compared to Dirk's model ? low seat height can be used by children or adult, hands touching the ground.
About the building itself : Front part steel 30x10x1.5mm with roller bearing pivot main beam, steel exhaust pipe 42mm outside diam. x1,5mm rear fork, steel 22mm outside diam. x 1,5mm mig welding Feels strong and rigid , for my weigth 80 kgs.
About the riding : Very odd, and a good challenge, children learn much more quickly than adults ! We started getting used (?) to it, after a few minutes/hours depending on age. Conclusion for now is it is ridable, low speed only, in open space. About the seat height, as mentioned in the freelist, we came to the same conclusion : the lowest the seat, the sharpest the balance. Having experienced we could ride it, at low speed, as it was, we are modifying seat height and trail. New goals : Pivot angle the same, 60 degrees. Trail, reduced to 14 cm, seat height + 10cms. Which will make this 20" python look exactly the same as Dirk's ! Do these figures remain good for him ? Or would he change them a bit for his own python, If he were to do it again ? It looks like Dirk got it right the first time, when it took us twice to reach the same result : a more forgiving ridable python, at last nearly (: >) ! Future will tell. Well done Dirk ; thanks Jurgën for the challenge ! Cordially Ghislain Pillet, Antibes, France.
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