[python] Re: another newcomer
- From: Tom <zzed28@xxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Wed, 24 Jan 2007 12:40:02 -0800 (PST)
Hi, I believe that the reason that taller
wheels have less rolling resistance in general is
due to the fact that they have to distort less,
to give the contact patch. The contact patch
which is dependent upon the overall weight and
the pressure of air in the tire. Flexing a tire,
takes energy from the pedaller, and more flex
means more energy to input. Thats why taller,
wider, flatter tires have less rolling
resistance, a bigger contact patch with less
overall tire distortion. The contact patch is
determined by the weight and the pressure, if the
total weight is two hundred pounds, then two
tires at one hundred psi will give a contact
patch on one square inch ,,each ,,by definition.
The hardness of the rubber is not the relevant
factor in this afaik, the overall compliance of
the tire in its entirety against the pavement is
what will count. That means that the more
compliant casing, plus tread rubber, the less the
rolling resistance. From over fifteen years and
forty thousand miles on recums, thats been my
experience. I personally am a fan of taller,
flatter treaded tires for my own bikes since they
dont have to distort so much against the pavement
to provide a good contact patch. Tom
--- Olaf Johansson <home@xxxxxxxxxxxxxxxxx>
wrote:
>
> I guess on a larger wheel more rubber is
> envolved in the flexing than
> on a smaller wheel.
>
> But saying that a softer compound would give
> less rolling
> resistance ... uh, uh. I am not yet willing to
> buy that. Anyone who
> let out 20 psi from the bike's tyre will notice
> an increased amount
> of sweat on their forehead.
>
>
> olaf
>
>
>
>
> On 24 jan 2007, at 14.14, dirk.bonne@xxxxxxx
> wrote:
>
> > Henry Thomas wrote:
> >> dirk.bonne@xxxxxxx wrote:
> >>> FYI: there has been documented measurements
> related to this.
> >>> Check out
> >>> this pdf:
> >>>
> >>>
>
http://www.ligfiets.net/redactie/meetligfietsengels.pdf
> >>>
> >>> Dirk
> >> Dirk, thanks for sharing this with us, it
> was a very interesting
> >> read. There isn't a lot of test data like
> this that I have found
> >> which is specifically dealing with
> recumbent.
> >>
> >> I am a bit confused about the tires. As I
> read it, larger rims
> >> (26") and firmer rubber compounds are better
> at higher pressures
> >> (110psi). However I thought that the
> Specialized Fat Boy was
> >> softer than the Schwalbe Stelvio Kevlar, or
> is that not the case.
> > <moz-screenshot-1.jpg>
> >
> >
> > I read the opposite out of this paragraph and
> thus no
> > contradiction. The supple rubber compounds
> are better. The stelvio
> > material is stiffer and also has a worse
> performance.
> >
> > What I think is interesting is that extreme
> height differences
> > between seat / BB are not needed. From 15 ->
> 25cm is no much
> > different in power. So you can just as well
> use 15cms (more
> > ergonomic). note, the measurement was made
> for seat angle of
> > 21degrees.
> >
> > Dirk
> >
>
>
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