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

  • From: George Durbridge <gdurbrid@xxxxxxxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Fri, 23 May 2008 07:43:41 +1000

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 “less round”."
> 
> 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 &lt;briannsmith@xxxxxxxxxxxxx&gt; 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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