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
> We are in full agreement on that particular law of physics. In addition to the
\r?\n> inertia factor influencing acceleration and deceleration, there is point
\r?\n> commonly referred to as friction. The lesser the amount of friction, the faster
\r?\n> you go, this as everybody knows is a thing which increases not proportionately,
\r?\n> but almost exponentially with increasing speed. Is the increase in resistance to
\r?\n> forward movement not roughly the square of the speed ? (I'll not mention
\r?\n> aerodynamics, because I get terminal 404 brain overload very quickly on this
\r?\n> sort of stuff).
\r?\n>
\r?\n> So where was I ? Probably that highly inflated thin tires are better in both
\r?\n> respects. Funnily, whereas you used to be able to find decent 700 x 20 or even
\r?\n> 19 tires, nowadays it's 700 x 23. This is due to the tremendous rigidity of the
\r?\n> modern wonder aluminium and carbon frames (something has to have some give to
\r?\n> make the machines rideable). This also explains the wider, heavier wheels to a
\r?\n> point, and rigidity in wheels as a element of loss-free transmission of energy
\r?\n> is another undisputable fact. It appears, unless one considers that all carbon
\r?\n> stuff is just market hyped cheapo (production cost) stuff, that the enormous
\r?\n> rigidity of the frame and wheels is more important in terms of performance gain
\r?\n> than the loss of "speed" from thicker tyres and heavier rims needed to cope with
\r?\n> the load. Now, where is my aspirin ? And if anybody can make sense of that one,
\r?\n> I give up trying to confuse the issue.
\r?\n>
\r?\n> My point in previous post you mailed CR on was that the easiest way to improve
\r?\n> a modest bicycle's performance is to put on some decent racing wheels and tyres.
\r?\n> In my case, '73 Campy record (High Flange),sewups on Wolber Super Champion rims
\r?\n> circa 1970 also.
\r?\n>
\r?\n> Regarding carbon, as I mentioned to another list member in oflist mail: for a
\r?\n> period I worked in the fishing tackle industry. Carbon rods came along, and we
\r?\n> were getting unexplained breakages left right and center. The boys finally
\r?\n> worked out that it took one tiny unnoticed knock for one micro fiber to break.
\r?\n> Then under load the nextone to it would go. Then the ones next door at a very
\r?\n> fast and increasing rate, until... snap. I saw a badly smashed frame in my local
\r?\n> shop, asked about the fall and was shown a pair of carbon bars that had snapped
\r?\n> for no apparant reason. All metals and materials suffer fatigue, you wouldn't
\r?\n> get me to put any wattage into a Caminade for example, but of all, steel remains
\r?\n> the best compromise. And the purists choice.
\r?\n>
\r?\n> I hope your Father Christmas wishlist gets through and you get a decent set of
\r?\n> 18 aero spoked carbon rims to Dura Ace to fit on your Herses :))
\r?\n>
\r?\n> Best regards
\r?\n> Nick Bordo, Aquitaine, France.
\r?\n> Date: Sat, 22 Sep 2007 08:48:40 -0700 (PDT)
\r?\n> From: Jerome & Elizabeth Moos
\r?\n> To: nick Bordo , classicrendezvous@bikelist.org
\r?\n> Subject: Re: [CR]Wheels make you faster, not frames.
\r?\n> Message-ID: <691612.10696.qm@web82205.mail.mud.yahoo.com>
\r?\n> In-Reply-To: <619292.24937.qm@web28007.mail.ukl.yahoo.com>
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\r?\n> Precedence: list
\r?\n> Message: 12
\r?\n>
\r?\n> Nick, we have had that discussion here, but maybe not recently. It is
\r?\n> an undisputed law of physics that weight far from the center of
\r?\n> rotation is much more important in acceleration and deceleration of a rotating
\r?\n> object than weight close to the center of rotation. Thus the weight
\r?\n> of the rim and tires are more critical than anything else, at least for
\r?\n> acceleration and braking on level ground.
\r?\n>
\r?\n> Don't know what you mean by "modern" wheels, but if you mean recently
\r?\n> made conventional alloy rims, they probably are not any lighter than a
\r?\n> lot of classic rims, and maybe a good bit heavier. In The Day there
\r?\n> were mass produced rims as light as 260 gm and probably some even
\r?\n> lighter. I think most more recent alloy rims are a good bit heavier. This is
\r?\n> mostly because the increasing number of rear cogs and the resulting
\r?\n> greater dish demanded stronger rims. But perhaps you are referring to
\r?\n> carbon fibre wheels, which perhaps do have much lighter rims. I really
\r?\n> don't have a clue about these, as I've never owned a pair, and have no
\r?\n> interest in doing so.
\r?\n>
\r?\n> Regards,
\r?\n>
\r?\n> Jerry Moos
\r?\n> Big Spring, TX
\r?\n>
\r?\n>
\r?\n>
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