[python] Re: Svar: Re: children's python

Hi Dirk,
here are the data for Luka's python:
Wheel size 305 (in front with a Schwalbe 47 mm).
pivot angle at 60°
Trail 114 mm
seat height 235 mm
Wheel base 1,04 m

cheers
Thomas


Den 04/08/2008 kl. 13.48 skrev Thomas Jahn:


Hej Dirk,
I am just back from vacation. Luka and me went by bike to Jottlands westcoast. He on the Brompton and me on the trike. Next time on the pythons. He did his first experience on the python yesterday. And although it looks rather challenging, I can already see some first progress. And he did not give up. Great! 

Den 15/07/2008 kl. 9.51 skrev dirk.bonne@xxxxxxx:


Thomas Paul Jahn wrote:

Hej Dirk,
Luka's first trial reminded a lot of his first time on an upright. He was very eager but it will take some time!!
The bike is a little too big still and so is the seat. He says, the seat is hard. The latter can be solved. The former will solve itself. The front part is rather heavy. With a Sram 5 speed hub. Am I surprised?! And the pivot made of brass bushes is pretty rigid. With his low weight, the self centering is minimal. Also the long rear part probably reduces the self centering. I wonder if I simply cut it shorter.
On my bike the self centering is also minimal - just enough to keep the front piece upright when sitting on it. I don't feel this is a problem at all, on the contrary, I like it because it allows for quick & sharp turns. Maybe Luka just needs the chance to learn it first a bit?
The weight of the front part should be as low as possible. Why should the sram hub have something to do with that? To me the bike looks already quite light - the tube at the front could be shortened, but then you would need to weld it back as Luca gets older.
You mean, the hub does not have any impact, because it is part of the rotating mass!?? I see.
You could shorten the rear, yes. It looks anyway disproportional long compared to the rest of the bike. But I think the self centering will get smaller. Do you have some data about the bike, I can calculate a comparisation to my bike. I need: 
* wheel size
* pivot  angle
* trail
* seat height
* wheel base


I will give you some data about the bike's geometry soon.....
And at the axis of the rear swing, or at the back wheel, I probably fix some supporting wheels to each side. So I don't have to walk bended down next to the bike, while Luka is doing his first exercises.
And the seat lean should be less inclined for him to reach the ground with his hands. I just hesitated reducing the inclination, as the beginner is not relaxed enough to go very recumbent. I seems now it would be better anyway... 

What do you think?
May be better to recline the seat (and not add support wheels), so he can touch the ground so he kind find his own balance. 

Luka and me agree!!
About the seat: It was extremely easy to make and is very rigid and stable. After assembling, I glued it with expoxy. I will definetly make one for my python as well, where I still lack the proper seat solution. The wooden seat is very easy to attach too. Because its construction can be adapted to the bike structure. It seems the idea for the seat brought me a large step further, while doing the final work on the bike. I strongly recommend it: 
http://hebike.borec.cz/sedlo.htm
Very interesting solution and very light!!! Don't understand the language but the scale I can read: 616gr. How well does the seat fit (lumber support)?
I am not an orthopaedist, I made the seat a little too big. But Luka is in a potentuially fast growing age. Now he just measures 126 cm. But soon..... 

Thomas


dirk

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