[python] Re: minimize rolling resistance, wheels tires air pressure
- From: Tim k <timfire2@xxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Wed, 24 Jan 2007 19:57:56 -0800 (PST)
It is my understanding that taller/larger wheels have less rolling resistance
because when they encounter bumps, they strike the bump at a shallower angle.
Umm, what I mean is, because the radius of the wheel is bigger, the tangent of
the radius at the point of contact is shallower. This allows bigger tires to
"roll over" bumps easier.
I do believe fatter/wider tires---for a given rim size---have less rolling
resistance becaused they deform less under pressure. However, that's assuming
the same air pressure. Skinny tires offset alot of their rolling resistence by
recommending higher air pressure. Higher air pressure causes the tire to deform
less. Though I haven't done the math, I doubt a 120 psi 1" tire has any more
rolling resistance than a 60 psi 2" tire. (I doubt the math is that simple, but
I hope you see my point). I can't say whether a 1" 120 psi tire has more or
less rolling resistance than a 1.25" 90 psi tire.
(Racers will also point out that skinny tires have less aero drag, which is the
biggest factor in speeds above 16-20 miles/hour. But that's a moot point if
you're a casual rider.)
I'm sure the rubber compound factors in somehow, but I don't know if it's
significant. It is also my strong suspicion that tread increases rolling
resistance, but I don't have any data to back that up.
Tom <zzed28@xxxxxxxxx> wrote:
--- Tom wrote:
> 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
> 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.
> > >
> > >
> > >
> > > 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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