Thanks for the link, DB. (dB stands for...)
I recall seeing the model before--which doesn't distinguish between wheel and overall weight. My only beef is that it assumes a linear relationship between weight and rolling resistance, which I don't feel is empirically supported.
Regards,
John Taglia Spending money on a new laptop that he would have been spending on an old Rossin and a Colnago. Or maybe I'll just buy a desk unit and the Rossin.
On Sun, 22 Apr 2001, dave bohm wrote:
> You may like this website:
>
> http://www.analyticcycling.com/
>
>
> It has lots of calculators for just this kind of thing and many others.
>
> Dave Bohm
> Bohemian
>
> ----- Original Message -----
> From: John Joseph Taglia
> To: Jerry & Liz Moos
> Cc: RMAugust@aol.com ; classicrendezvous@bikelist.org
> Sent: Sunday, April 22, 2001 3:19 PM
> Subject: Re: [CR]Re: Reducing the "Polar Moment of Inertia"
>
>
> This is interesting, but fails to take into account the only
> acceleration that is material: the acceleration of bike and rider. Unitl
> I see an equation, I will continue to believe that weigh of bike is pretty
> much immmaterial, and that wheel matters no more than any other.
>
> I guess I don't think it is too much to ask for proof via an equation.
> (And the skater analoqy is flawed as speed stays constant--larger radiusx
> slower rpm=smaller radius x higher rpm. So no net change in enery or
> speed.)
>
>
> On Sat, 21 Apr 2001, Jerry & Liz Moos wrote:
>
> > Thanks, Randy, guess I won't have to find my Engineering Dynamics book after
> > all. To elaborate, the inertia is a product of the weight (actually the mass)
> > and the distance from the axis of rotation, and inertia determines the ease with
> > which the wheel can accelerate or decelerate (brake). Since the hub is very
> > close to the axis of rotation, its weight is almost irrelevant. Since the rims
> > and tires are at the greatest distance from the axis, a small decrease in their
> > mass leads to a large decrease in inertia, so their weight is all-important.
> > Also, since the weight of the bike and rider acts thru the axle, it isn't
> > important in acceleration either. Total weight does play a small role in riding
> > at a steady pace, as it does affect rolling friction of the tires somewhat. It
> > matters a lot in climbing, since neglecting friction and wind resistance, the
> > energy required to lift the bike and rider to the top of the climb is the product
> > of the total weight and the vertical distance climbed. This is why track
> > sprinters, or road sprinters for that matter, are usually heavily muscled types,
> > since they have more power output, and their weight is no handicap, as the weight
> > of the rims and tires and the power applied mostly determines acceleration. In
> > climbing, however, it is the ratio of power to weight that matters, so a 130 lb
> > rider only has to have 2/3 of the power output of a 200 lb rider to make it to
> > the summit first. Never thought polar moment could explain why Cipollini
> > thrashes Pantani in the sprint, but Pantani destroys him on the l'Alpe d'Huez did
> > you?
> >
> > Regards,
> >
> > Jerry Moos
> >
> > RMAugust@aol.com wrote:
> >
> > > << Why doesn't someone offer some proof that weight matters all that much to
> > > begin with and that rim and tire weight matters more. All I see are
> > > unsubstantiated claims. I say until some one can prove different rotating
> > > weight doesn't matter more, and that weight in general doesn't matter all
> > > that much.
> > > >>
> > > Given two wheels of equal weight, one with a greater proportion of its weight
> > > in its rim and tire will have a greater polar moment of inertia which
> > > therefore will accelerate at a slower rate of speed. A good example of this
> > > is an ice skater rotating with arms extended (high polar moment) and then
> > > moving the arms in very close to the body (lower polar moment). The result is
> > > that the speed of rotation increases dramatically.
> > >
> > > Wind resistance plays a small role in this but mainly it's the reduction of
> > > the polar moment. In the case of wheels, reducing the polar moment makes a
> > > bike feel more fleet and in competition can give one an actual speed
> > > advantage off the line. That's the proof of why reducing rim and tire weight
> > > matters more than reducing weight in general.
> > >
> > > As to reducing weight in general, I think it's generally known that, given no
> > > other variables, a lighter bike will be more efficient to move owing to fact
> > > that less calories are required to fuel it.
> > >
> > > Randy
> > > Corral De Tierra, Ca.
> > >
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> >
> >
> >
> >
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