700/23 vs 700/25 tires ?

On Feb 20, 11:47*am, "Robert Chung"
wrote:
Tim McNamara wrote:
Third, how significant were these changes? In a racing context, the
time benefit we're seeing can be quite significant. The benefit for
switching from a P2K (already a fairly aero bike) to a P3C was
about 2 secs/km. In every one of Armstrong's TdF ITTs from 1999 to
2005 except one, he won or lost by less than that.

So why doesn't everyone ride one of these bikes and why isn't the guy
at the top of the results in every TT the guy who is on one of them?

That's Frank's argument, and it's a straw man. First, pros don't get to
choose the bike they ride (unless they're good enough to get their own
sponsorship deal *and* that sponsor happens to make the bike they would have
chosen). Second, not every rider has the same power and same position.
That's why we do controlled tests. And third, in situations where riders
*do* get to choose their bikes--well, look at the numbers from the "Kona
bike count" which tracks the brand of bikes used for the Hawaii Ironman (the
de facto world championship):http://www.slowtwitch.com/News/Kona_..._count_77.html

Interestingly, the top pros in that sport are also sponsored but I don't
think Cervelo was involved in any of those sponsorship deals (they were
already committed to CSC for the Pro Tour).

Still wearing the TT / Tri blinders, I see. Show us data from road
racing.

Robert, there is more to bicycling, and to bicycle racing, than TTs
and tris. You should get out more!

- Frank Krygowski

wrote:

There's a reasonable chance he would have won Stage 1 of the 2005
TdF if he had.

Maybe Lance would've won more road races if he'd ridden Cervelos
instead of Treks, but probably not Stage 1 of the 2005 TdF 9a time
trial). Lance's Trek TTX prototype has been measured to have less drag
than the Cervelo P3C.

The "narrow" bike? Wasn't that the one that LANCE didn't use?

In article ,
"Robert Chung" wrote:

Tim McNamara wrote:

I'll read through it again later today when I have more time and
hopefully with some repetitions it will become clearer. Some of it
looked quite interesting (I was intrigued by the
modeled-versus-measured speed figure because of the periodicity in
the measured speed).

That periodicity was because the measured speed was on a banked
velodrome track. The wheels speed up in the turns.

Good point. My recollection of the sensations of racing on the Blaine
velodrome is that the bike feels light and accelerates a bit going into
the turns and feels heavier and slows down existing from the turns. No
bike computer, though, to verify.

The powerpoint presentation wasn't meant to be defnitive. However,
it's an okay summary and, importantly, it gives pointers to many
source articles if you want to read them.

It's an OK summary with holes in it, which presumably were filled in by
the speech itself. As a presentation I suspect it was probably very
good indeed. However, the good fit achieved between the model and the
measurements was your point, I am sure, and it did show that. Thanks!

On Fri, 20 Feb 2009 09:35:27 -0600, Tim McNamara
wrote:

JT, you seem to misunderstand how these discussions work.

I know you're a piece of work.

On Fri, 20 Feb 2009 09:01:40 -0800 (PST), Frank Krygowski
wrote:
[tiny difference in rolling resistance]
It will certainly never add significantly to the
person's enjoyment of a recreational ride.

Thanks for clearing that up for us again Frank.

I was getting the urge to post about how critical tire choice is to
happiness on rec rides, but you're keeping me honest.

Thanks.

In article ,
"Robert Chung" wrote:

Ken Freeman wrote:

Another point: does a bike powermeter have the resolution and
accuracy to show the difference between the drag contribution of
different tires, from road data, with uncontrolled wind velocity
and unknown random noise content? It seems to me the difference in
watts usually a very small fraction of the rider's power output.

The answer is: it depends. Some power meters are better suited to
these kinds of tests than others. Good experimental technique means
you try to do these things on non-windy days. Good analytical
technique lets you identify the random component. The method
discussed immediately above in the Martin article produces estimates
of CdA that have been validated by wind tunnel results, and the
technique discussed in the ST thread has been shown to be consistent
with the Martin method. Repeatability appears to be quite good: Tom
reports that he gets repeated estimates of CdA to within .001-.002
m^2. In other tests, a different guy put a 5cm x 5cm square on his
bike (i.e., .0025 m^2) and estimated the change in CdA at .003 m^2
(i.e., an error of .0005 m^2). The Crr estimates have also been shown
to be consistent with those found in the roller tests described
elsewhere in this thread.

What should appear in comparing the steel drum tests for rolling
resistance to the measurements of power losses from rolling resistance
using a power meter is that while the absolute rolling resistance is
probably different (one would expect absolute RR to be lower on a steel
drum than on asphalt), the ordinal differences between tires should be
the same. At least as far as can be told within reasonable confidence,
being that all measurements are prone to some error.

And thanks again to Robert for referencing those links.

So the references made by Robert and Ben have all focused on three
things that we have already agreed upon: weight, rolling resistance
and aerodynamic drag. Since those have long since been stipulated,
being that they have been well known for many years, what else we got
to talk about?

If I install a Shimano derailleur with 11 tooth jockey wheels, am I
gonna take 20 minutes off my 200 km time? If I use a titanium nitride
coated 10 speed cassette, am I going to be faster than with my 8 speed
chromed cassette? If so, how much? What other technological benefits
can I buy that will make me faster (other than EPO and the like, of
course)?

In article ,
"Robert Chung" wrote:

Tim McNamara wrote:
Third, how significant were these changes? In a racing context,
the time benefit we're seeing can be quite significant. The
benefit for switching from a P2K (already a fairly aero bike) to
a P3C was about 2 secs/km. In every one of Armstrong's TdF ITTs
from 1999 to 2005 except one, he won or lost by less than that.

So why doesn't everyone ride one of these bikes and why isn't the
guy at the top of the results in every TT the guy who is on one of
them?

That's Frank's argument, and it's a straw man. First, pros don't get
to choose the bike they ride (unless they're good enough to get their
own sponsorship deal *and* that sponsor happens to make the bike they
would have chosen). Second, not every rider has the same power and
same position. That's why we do controlled tests. And third, in
situations where riders *do* get to choose their bikes--well, look at
the numbers from the "Kona bike count" which tracks the brand of
bikes used for the Hawaii Ironman (the de facto world championship):
http://www.slowtwitch.com/News/Kona_..._count_77.html

Interestingly, the top pros in that sport are also sponsored but I
don't think Cervelo was involved in any of those sponsorship deals
(they were already committed to CSC for the Pro Tour).

So what you're saying is that it's not really about the bike.

Tim McNamara wrote:

That periodicity was because the measured speed was on a banked
velodrome track. The wheels speed up in the turns.

Good point. My recollection of the sensations of racing on the Blaine
velodrome is that the bike feels light and accelerates a bit going
into the turns and feels heavier and slows down existing from the
turns. No bike computer, though, to verify.

Sundquist mentions "floating through the turns" and "punching it onto the
straights."

In article
,
Frank Krygowski wrote:

On Feb 20, 1:39*am, Ryan Cousineau wrote:
In article
,
*Frank Krygowski wrote:

Personally, I think it's crazy to continue pretending that racers
must never (or never do) dismiss an advantage as negligible.
*That point has been so easily, and so often, disproven that the
"nothing is negligible" crew should formally concede.

We can then concentrate on the "small changes can add up to big
changes" idea. *That's more interesting, since there are some
situations in which that has validity and some where it doesn't.

That'd be great! Don't change the thread title, though: we're going
for the record.

OK, regarding small changes and big changes, there is a sort of
paradox to deal with. We know (well, most people know) that reducing
bike+rider mass, rolling resistance, or aero drag by 0.5% will never
be shown to improve a rider's results in a road race, crit race, or
matched sprint.

The data provided in one of Robert's links suggested that a significant
difference could be found in something like match sprinting, which is
often separated by .0x seconds. In roads and crits, the difference
would be equivocal due to the aerodynamic and psychological effects of
pack riding. The latter is something that isn't addressable in this
thread and may not be "modelable."

It will certainly never add significantly to the
person's enjoyment of a recreational ride.

Probably not, but the focus of the benefits under discussion is really
in the competitive arena. A more comfortable saddle and properly
adjusted bike fit are probably the biggest improvements that can be
provided to recreational cyclists.

Tim McNamara wrote:
In article ,
"Robert Chung" wrote:

Ken Freeman wrote:

Another point: does a bike powermeter have the resolution and
accuracy to show the difference between the drag contribution of
different tires, from road data, with uncontrolled wind velocity
and unknown random noise content? It seems to me the difference in
watts usually a very small fraction of the rider's power output.

The answer is: it depends. Some power meters are better suited to
these kinds of tests than others. Good experimental technique means
you try to do these things on non-windy days. Good analytical
technique lets you identify the random component. The method
discussed immediately above in the Martin article produces estimates
of CdA that have been validated by wind tunnel results, and the
technique discussed in the ST thread has been shown to be consistent
with the Martin method. Repeatability appears to be quite good: Tom
reports that he gets repeated estimates of CdA to within .001-.002
m^2. In other tests, a different guy put a 5cm x 5cm square on his
bike (i.e., .0025 m^2) and estimated the change in CdA at .003 m^2
(i.e., an error of .0005 m^2). The Crr estimates have also been shown
to be consistent with those found in the roller tests described
elsewhere in this thread.

What should appear in comparing the steel drum tests for rolling
resistance to the measurements of power losses from rolling resistance
using a power meter is that while the absolute rolling resistance is
probably different (one would expect absolute RR to be lower on a
steel drum than on asphalt), the ordinal differences between tires
should be the same. At least as far as can be told within reasonable
confidence, being that all measurements are prone to some error.

Yeah, I mentioned that earlier in the thread, and also in that thread a few
months ago where you (I think it was you) refused to look at the
roller-based estimates. Crr on actual roads will depend on both the tire and
the road. Guys who've tried to validate the AFM estimates report that on
"typical" roads in their areas the estimated Crr's vary between about 1.5x
and 2x the roller estimates but that when the rankings were significantly
different then that ordering is preserved.

So the references made by Robert and Ben have all focused on three
things that we have already agreed upon: weight, rolling resistance
and aerodynamic drag. Since those have long since been stipulated,
being that they have been well known for many years, what else we got
to talk about?

Not much, really. That's why I focus on CdA and Crr -- lots of others have
already focused on mass, but CdA and Crr are much harder to measure than
mass so they get less discussion. Especially here on rbt. The only remaining
issue is that Frank (and you) have been contending that negligible +
negligible + negligible = negligible. Frank has said that the benefit of
aero seatposts, and aero waterbottles, and aero brakes, and aero headtubes,
and aero rims, and aero frame tubes are each negligible. The ST thread shows
that the sum effect of several of those things is non-negligible (the rims
and water bottle weren't changed in that test).