I mostly agree, but I'd add that the assumption that fat tires are aerodynamically "draggier" isn't a safe one to make. Aero can be maddeningly counterintuitive, even identical shapes are subject to scaling (Reynold's Number) issues. Remember lenticular front wheels? They sure didn't look aero. It wouldn't surprise me a bit if fat tires (the rim profile's interaction with the tire's will also come into play) were found to be more aero. The wheel is interacting with the rest of the bike and the rider aerodynamically in turbulent/chaotic ways that can't be visualized in terms of the usual streamlines in a free flow. But you can't really tell without empirical data to analyse. And good, valid, repeatable aero data of mixed flows is famously difficult to acquire.
Subjectively, nominal 30mm Grand Bois tires at ~90psi feel very fast to me. Even compared to 20mm skinnies pumped up to 120+psi. And not getting beat up and having to lift your butt of the saddle for every bump is fast in a secondary/tertiary way I think. Plus good fat tires seem to corner faster- which is a flavor of fast and I'm less apt to consciously slow when I get to some funky road surface on wides.
Kurt Sperry Bellingham WA USA
On 9/22/07, hersefan@comcast.net <hersefan@comcast.net> wrote:
>
> Tires are getting wider because rolling resistance, all else equal, is
> lower for wider tires (assuming identical casing and pressure). Of course
> we run wide tires at lower pressures, but the inverse of this statement is
> that it is possible to have a wide tire at lower pressure deliver the same
> rolling resistance as a skinny tire at high pressure - but the comfort is
> much greater on the wide tire!
>
> So again, why aren't all race bikes using wide tires? Because everthing
> is a trade-off. Wider tires are heavier and have greater wind
> resistance. And acceleration is most important for those in a race. So
> where the typical non-competitive rider is best on a 25mm to perhaps 30mm
> 700c, the racer may go a big narrower. But the 19mm and 20mm tires were
> just too silly - the weight and aero benefits even for many pro riders to
> not overcome the relatively high rolling resistance such a tire yields.
>
> Now if the road is increadibly smooth, and the rider's speed is extreamly
> high, very narrow tires might become optimal. Its all a math
> problem. Folks just get tripped up because they often don't understand that
> rolling resistance is caused by the tire forming the contact patch, and that
> wide "short" (with wide tires)contact patches are easier to form that skinny
> long (with skinny tires) ones.
>
> And finally, one must remember that while heavy wheels are difficult to
> accelerate, they carry more momentum and don't deaccelerate as easily. That
> is why for time trial events at steady high speeds, wheel weight is actually
> far less important than rolling resistance or tire pressure. I also never
> understood why heavy aero wheels caught on years ago because I didn't think
> about the physics correctly - its because for a relatively flat time trial
> situation, rotating weight is Both friend and foe - so it really doesn't
> matter much!
>
> Mike Kone in Boulder CO
>
>
>
> -------------- Original message --------------
> From: nick Bordo <nicbordeaux@yahoo.fr>
>
> > We are in full agreement on that particular law of physics. In addition
> to the
> > inertia factor influencing acceleration and deceleration, there is point
> > commonly referred to as friction. The lesser the amount of friction, the
> faster
> > you go, this as everybody knows is a thing which increases not
> proportionately,
> > but almost exponentially with increasing speed. Is the increase in
> resistance to
> > forward movement not roughly the square of the speed ? (I'll not mention
> > aerodynamics, because I get terminal 404 brain overload very quickly on
> this
> > sort of stuff).
> >
> > So where was I ? Probably that highly inflated thin tires are better in
> both
> > respects. Funnily, whereas you used to be able to find decent 700 x 20
> or even
> > 19 tires, nowadays it's 700 x 23. This is due to the tremendous rigidity
> of the
> > modern wonder aluminium and carbon frames (something has to have some
> give to
> > make the machines rideable). This also explains the wider, heavier
> wheels to a
> > point, and rigidity in wheels as a element of loss-free transmission of
> energy
> > is another undisputable fact. It appears, unless one considers that all
> carbon
> > stuff is just market hyped cheapo (production cost) stuff, that the
> enormous
> > rigidity of the frame and wheels is more important in terms of
> performance gain
> > than the loss of "speed" from thicker tyres and heavier rims needed to
> cope with
> > the load. Now, where is my aspirin ? And if anybody can make sense of
> that one,
> > I give up trying to confuse the issue.
> >
> > My point in previous post you mailed CR on was that the easiest way to
> improve
> > a modest bicycle's performance is to put on some decent racing wheels
> and tyres.
> > In my case, '73 Campy record (High Flange),sewups on Wolber Super
> Champion rims
> > circa 1970 also.
> >
> > Regarding carbon, as I mentioned to another list member in oflist mail:
> for a
> > period I worked in the fishing tackle industry. Carbon rods came along,
> and we
> > were getting unexplained breakages left right and center. The boys
> finally
> > worked out that it took one tiny unnoticed knock for one micro fiber to
> break.
> > Then under load the nextone to it would go. Then the ones next door at a
> very
> > fast and increasing rate, until... snap. I saw a badly smashed frame in
> my local
> > shop, asked about the fall and was shown a pair of carbon bars that had
> snapped
> > for no apparant reason. All metals and materials suffer fatigue, you
> wouldn't
> > get me to put any wattage into a Caminade for example, but of all, steel
> remains
> > the best compromise. And the purists choice.
> >
> > I hope your Father Christmas wishlist gets through and you get a decent
> set of
> > 18 aero spoked carbon rims to Dura Ace to fit on your Herses :))
> >
> > Best regards
> > Nick Bordo, Aquitaine, France.
> > Date: Sat, 22 Sep 2007 08:48:40 -0700 (PDT)
> > From: Jerome & Elizabeth Moos
> > To: nick Bordo , classicrendezvous@bikelist.org
> > Subject: Re: [CR]Wheels make you faster, not frames.
> > Message-ID: <691612.10696.qm@web82205.mail.mud.yahoo.com>
> > In-Reply-To: <619292.24937.qm@web28007.mail.ukl.yahoo.com>
> > Content-Type: text/plain; charset=iso-8859-1
> > MIME-Version: 1.0
> > Content-Transfer-Encoding: 8bit
> > Precedence: list
> > Message: 12
> >
> > Nick, we have had that discussion here, but maybe not recently. It is
> > an undisputed law of physics that weight far from the center of
> > rotation is much more important in acceleration and deceleration of a
> rotating
> > object than weight close to the center of rotation. Thus the weight
> > of the rim and tires are more critical than anything else, at least for
> > acceleration and braking on level ground.
> >
> > Don't know what you mean by "modern" wheels, but if you mean recently
> > made conventional alloy rims, they probably are not any lighter than a
> > lot of classic rims, and maybe a good bit heavier. In The Day there
> > were mass produced rims as light as 260 gm and probably some even
> > lighter. I think most more recent alloy rims are a good bit heavier.
> This is
> > mostly because the increasing number of rear cogs and the resulting
> > greater dish demanded stronger rims. But perhaps you are referring to
> > carbon fibre wheels, which perhaps do have much lighter rims. I really
> > don't have a clue about these, as I've never owned a pair, and have no
> > interest in doing so.
> >
> > Regards,
> >
> > Jerry Moos
> > Big Spring, TX
> >
> >
> >
> > ---------------------------------
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