[python] Re: Svar: Re: New Python - 20" or 26"?

I believe the Moulton record was done behind a specially designed automobile that had wings built on it to shield the rider.
Also, that record hasn't been challenged nearly as much as the one hour record. I don't think any professional cyclists have attempted it. 




On 22-May-08, at 2:43 PM, George Durbridge wrote:


Minor details of construction and layout will affect the minimum on
different bikes, so a range of 84 - 86 cm is not unreasonable. On your 
first bike, it may be sensible to use a smaller wheel if you are in
doubt: too small a wheel may make the bike less efficient than it could 
have been, but too large may mean you cannot ride it.
The Schwalbe page is helpful, thanks Dirk, but rolling resistance isn't usually the main problem. On really smooth road, with good tyres pumped 
to 100 psi, it is hard to tell the difference between the rolling
resistance of 26" tyres and 20" tyres.  And 26" knobbies generate more
rolling resistance than 20" Marathons.  But on potholes or gravel, the
smaller wheel obviously loses a lot more energy over the bumps than a
larger wheel with a similar tyre. Moulton dealt with this by the use of 
suspension.

On Thu, 2008-05-22 at 22:50 +0200, dirk.bonne@xxxxxxx wrote:

Ok right I didn't think about the inseam. There is a table at

    http://en.openbike.org/wiki/Wheel_Sizes
this states that 84cm is the minimum for 170mm cranks with 26" wheels. 
Now I am not sure which is right.

About the rolling resistance, I quote from the schwalbe website
(english version)

"Rolling resistance is the energy that is lost when the tire is
rolling and the main reason for loss of energy is the constant
deformation of the tire."
...
"Small diameter tires have a higher rolling resistance at the same
tire pressure, because tire deformation is proportionally more
important, in other words the tire is â??less roundâ??."

There are other elements:

    http://www.schwalbetires.com/tech_info/rolling_resistance

dirk

Thomas Paul Jahn wrote:
Yes, 20" wheels fit shorter legs. I would not be able to use 26". When I remember well, the minimum inseam height was 86 cm with 26" according to Jürgen. 

and hej Dirk,
why do you mention higher rolling resistance with 20" compared to 26"? Do you think, the axis will turn faster at the same speed and thereby increase resistance? So what about the reduced air resistance with 20" then. That should be much more important. And the reduction in weight? And in particular for the python, with 20" wheels you reduce the distance between front axi and pivot, which I believe gives a lot of stability. 
So even when I was 1,90 m, I would choose 20". Definitely!
By the way: why does Moulton have the world record on the upright bike. Not inspite of 17" wheels. Rather because of it. 
cheers
Thomas



brian smith <briannsmith@xxxxxxxxxxxxx> 22-05-08 17:02 >>>
Is not leg length an important factor in deciding if one can use a 26" 
front wheel ?
Just wondering
Oupa in SC USA

On Thursday, May 22, 2008, at 04:57  AM, dirk.bonne@xxxxxxx wrote:






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