[python] Re: minimize rolling resistance, wheels tires air pressure
- From: Tom <zzed28@xxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Thu, 25 Jan 2007 09:23:23 -0800 (PST)
Thanks Tim for clarifying that, I had overlooked
the additional idea that taller wheels will fall
less far into rough pavement. In my area, there
are lots of rough roads, and I know that between
the roughness and the dodging of many bumps with
steering, those roads are slowwwwwwwwwwwww !
I too have experimented with the wide narrow hi
and low pressure factors. I find that most tires
can be ridden as high as 120 psi, even 1.75
tires. I am not making a blanket statement, and
dont recommend that anyone else do such a thing,
but its been done, and safely by me in
experiments as well as my usual twenty mile
rides. Ive even found that the tires that sell
for about six bux at walmart in the twenty by
1.75 can be ridden at a hundred psi when marked
as 45psi on the sidewalls. That particular tire
had a good feel at that pressure and seemed to
roll very nicely, comparable to a comp pool in my
experience. The comp pool is a favorite of mine
when I cant find a flatter inverse treaded tire.
The inverse treaded tires from nashbar and
avocet are nice and flat, but I havent tested
them at serious cornering angles at all since I
tend to corner slowly. I usually run tires at a
pressure that causes them to just barely distort
the sidewall visually when the rider is seated in
position. When putting on a new tire, I have a
helper watch the sidewall closely while I sit on
the bike, then incrementally put air into it,
until the sidewall doesnt distort at all visually
when I sit on the bike, then let 5 psi out and
see if there is any tiny distortion, if so, thats
my riding pressure for that tire. Ive found that
going to a higher pressure, which produces an
UNdistorted sidewall, generall does make the tire
slightly easier rolling, but tends to make the
tire feel bouncy over the rough stuff. This is
what works for me with my local loads and roads.
smile.
2@xxxxxxxxx> wrote:
> 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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>
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