Bikes: 700/23 vs 700/25 tires?

[Chalo]

>
> Tire losses are in flexing the sidewall and flexing the tread.
> Thinner side walls dissipate less energy flexing.
> Same for tread. But a wider tire cannot have a sidewall as
> thin as a narrower tire because of the way the forces work.
> Therefore wider tires have thicker casing and dissipate more
> energy flexing.

Don't think so. Fatter tires have to distort much less to establish a
given contact patch. Even if there is less rubber being worked in a
narrow tire, it is being worked to a much higher degree of
deflection. This accounts for the roller tests Jobst Brandt has
posted many times which show that wider tires of equal construction
exhibit lower rolling resistance than narrower ones.

> The sweet spot for low rolling resistance
> is around 21-25 mm width tires.

That's entirely dependent upon load and surface quality. Just like a
suspended vehicle can maintain a higher speed than an unsuspended
vehicle past a certain function of surface roughness and speed, a
wider, softer tire can be faster when surface quality is taken into
account. Were that not the case, MTB racers could use 1.5" tires or
even road bike tires. But in fact they would not be competitive if
they did so.

> I see the experiment every day. Rolling along our streets,
> stop pedaling and continue to gain on other bicycles with
> wide tires.

I do that on 700x60 tires, merely on the basis of my superior
mass:frontal area ratio and the fact that my bike is in good running
condition. It's the same whether I'm running 700x32 Paselas or 700x60
Big Apples.

Chalo

[dustoyevsky]

On Jan 30, 1:21*pm, Chalo <chalo.col...@**********> wrote:


> I really doubt measurement has much to do with it. *As I've pointed
> out, early 20th century racers used tires about 1.5" wide on their
> bikes, thinking that was faster than the alternatives.

Tire construction, materials and technology, were not nearly as good
as in recent times. Notice multiple spare tires being carried on old
autos; my grandmother told me they'd usually have at least one flat
per excursion. Of course roads (speaking of the 20's) were not the
equal of the good roads of more recent times.

>*Twenty years
> ago, many racers were using 19s and 20s on their bikes, thinking that
> was faster. *Now they're using 23s, thinking that's faster.
>
> Is every such fashion change for the faster? *How could it be? *But
> that's the nature of fashion-- as long as everybody adopts it, then
> you never have to know one way or the other.

I think the "too many flats" equation was finally solved <g>.

>*I'm sure that if Lance
> in his heyday had used 700x18s and won on them, everybody else would
> have switched to those. *And if he'd used 700x32s and won on them,
> everybody would have switched to those.

Flip side, Lance didn't "switch", probably for good reason.

IMHO it goes to flats-- you use the smallest (lightest, most aero)
tire you can that doesn't "flat too often".
Note the handling problems seen on the TT bikes, where they're using
small-section tires pumped hard. That tells you something about
"priorities", which may have a basis in wind tunnel testing-- and
probably does with LanceCo.

> Thus we'll never really know whether a high quality race tire built
> in 28mm or 32mm casing width would be as fast in races as 23mm or 25mm
> tires.

You have a tire bias, Chalo!
--D-y

[Dan O]

On Jan 28, 7:27 pm, jeffreybike <jeffreyb...**********m> wrote:
> Is there any real difference between 23mm and 25mm tires as far as
> speed. Will 2mm make you that slower or faster?

Not significantly - that's for sure.

To give the absolute simpleton perspective, when I was a kid, riding
20 x 1.75 tires, I found that higher pressure resulted in lower
rolling resistance and faster acceleration with less effort. I note
that narrower tires generally have higher max pressure ratings.

I run 28's on the bike I ride most. These tires are not a speed
constraint for me. There's room for at least 32's, I think, and will
probably try some eventually.

I believe that between tires that close in size, materials and
construction, including maybe esp the casing, are more important to
how tires ride.

I have 23's on my go-fast bike. They make the bike look really racy,
and the bike does go fast. I wouldn't want to ride on anything
smaller, and may very well get some 25's when I replace them.

[Chalo]

>
> Chalo wrote:
> >
> > So is there any evidence that wholesome-sized riders like Miguel
> > Indurain and Magnus Bäckstedt and Ken Carpenter have used tires
> > different in size than those of their competitors, some of whom were
> > not much more than half their weight? Who was using the wrong sized
> > tire, the big racers or the small racers? Did that make the
> > difference between racing success and failure?
>
> Back in the day, Allan Peiper wrote in his column in ProCycling or Cycle
> Sport that Indurain rode the Tour on 18 mm tires.
>
> Hmm. If 23s are faster than 25s, then 18s would be faster than 23s, and
> 10s would be faster than 18s, and no tires would be the fastest of all.

Perhaps we should use a Big Mig index for tire size: Your optimum
sporting tire width in millimeters is your weight in pounds divided by
11.

[Tim McNamara]

Andrew Price <ajprice@free.fr> writes:

> On Sun, 01 Feb 2009 11:53:21 -0600, Tim McNamara
> <timmcn@bitstream.net> wrote:
>
> [--]
>
>>Tire sizes in bicycles are nominal at best. This has improved
>>somewhat with the introduction of ISO sizes (e.g., 25-622 for a 700C
>>x 25 tire) but there is still frequently about a 2 mm difference
>>between various brands of tires marked as the same size, when
>>mounted on the same rims.
>
> That is certainly true. Fitting Vittoria 700x23c on my Campagnolo
> rims is a nightmare, whereas Michelin tyres fit easily.

I was referring to the width of the mounted, inflated tire. For
example, Michelin tires tend to run about 1 mm wider than their
nomimal size whereas Continental tires tend to run about 1-2 mm
smaller. (That may not be true now, I haven't used Continentals in
years).

However, your point about some tires fitting more tightly than others,
as determined by the length of the bead, is also well-known to be
true. Combined with some rims being a hair oversized or a bit
undersized, there are combinations of tires and rims that can be a
nightmare of not being able to get the tire on or off with reasonable
ease or of not being able to keep the tire seated at pressure.

Hmm. In retrospect I think I have seen and heard of there being less
variation in terms of rim diameter among Mavic rims than among Sun
rims and Velocity rims. Torelli Master rims had a batch that were
slightly oversized and had a reputation for being extremely difficult
to mount tires.

[Chalo]

>
> Chalo wrote:
> >
> > I find my own personal sweet spot for speed and tire reliability in
> > the 35-40mm range of tire width. *I don't assume this would be the
> > same for other riders. *However, I have spent a lot of time with the
> > urban cycling community in both Seattle and Austin, and I have seen
> > again and again young messengers and self-styled sport riders come to
> > the realization that 28mm tires are no slower than narrower ones, but
> > are way better at getting you there with air still in the tires and
> > wheels intact. *I don't think this is mere coincidence. *I do think
> > that they often stop at 28mm because so many of their bikes can't
> > accept a fatter tire than that.
>
> The real change over is at 25 mm. Above that casings
> _must_ be made thicker. I ride 28 and 25. The 28 with
> the thin flexible casing is very good, particularly for
> utility riding. The 25 with the very good casing is better.

I believe that a good 25mm tire has lower rolling resistance than a
thicker 28mm tire. But there is a trade between raw natural RR and
effective RR, which is to say tire losses plus the energy transmitted
to the rider as shock that is subtracted from the bike's kinetic
energy. At a certain surface roughness and speed, 28mm becomes
faster, even if it has a touch more natural RR on a smooth surface.
Turn up the surface roughness even more, and an even fatter tire
becomes faster. Hence MTBs.

People who drive their bikes to the smoothest roads they can find, so
they can ride their pretend racing bikes and scatter goo packets and
CO2 cartridges all over the place, are generally able to use smaller
tires than folks who ride on the streets that run between where they
are and where they want to go.

Chalo

[dustoyevsky]

On Feb 2, 8:02*pm, carlfo...@************ wrote:

> After all, what else could explain Armstrong's margin over Ullrich up
> the Alp d'Huez?

Weight reduction I think it's agreed was key there.

Measured in bratwurst per fortnight.

<g>

--D-y

[landotter]

On Feb 2, 9:14*pm, "dustoyev...@mac.com" <dustoyev...@mac.com> wrote:
> On Feb 2, 8:02*pm, carlfo...@************ wrote:
>
> > After all, what else could explain Armstrong's margin over Ullrich up
> > the Alp d'Huez?
>
> Weight reduction I think it's agreed was key there.
>
> Measured in bratwurst per fortnight.
>
> <g>
>

B/pF

[Frank Krygowski]

On Feb 2, 8:56*pm, John Forrest Tomlinson <usenetrem...@jt10000.com>
wrote:
> On Mon, 2 Feb 2009 08:38:10 -0800 (PST), Frank Krygowski
> <frkry...@**********> wrote:
> >On Feb 1, 12:35=A0pm, John Forrest Tomlinson <usenetrem...@jt10000.com>
> >wrote:
> >> but then again I'm not a scientist...
>
> >I know.
>
> >I don't recall what field you work in. *I wonder how decisions are
> >made within that field? *If a certain strategy with certain costs
> >never produces a detectable benefit, do you still spend money on it?
>
> If a out of a certain 10 strategies we believe frome experience have a
> chance to produce some benefit, though it's likely that only about
> half wil beneiftl, half will do nothing (and perhaps one might even be
> negative), but we can't measure it precisely enough to know which, and
> we have the resources to do 8 or 10, what do we do?

John, you'll need to clean that up and post again. I can't decipher
your intended meaning.

- Frank Krygowski

[Nick L Plate]

On Feb 3, 6:14*am, carlfo...@************ wrote:

>
> Consider the title of this thread. Has anyone presented any evidence
> that a 700/23 tire of the same quality as a 700/25 tire will make any
> practical difference _overall_ in a 100-mile race? One might be more
> aerodynamic, the other might handle better, rolling resistance might
> vary this way or that, the results might be different depending the
> wheels used, and I suspect that the riders would have trouble saying
> what tire pressure they used and why.
>

I believe the best that can be done is a rolldown test upon the
course. A relatively shallow downgrade is what is called for. The
rider in question must use all the same equipment intended for race
day. Variation of pressures on individual tyres are performed until
the quickest time between two points is recorded. The speed at the
start of the timed section must be close to speed on race day, and
identical for each record. Each tyre and pressure combination needs 5
records. Start with maximum pressure, say 120psi, and work down until
the timings show an obvious increase, the previous pressure is your
best for that tyre/road. Do this for all tyres, finding the optimal
pressure for both front and rear individually. Hopefully this will
also provide sufficient grip, should it rain.