Nobody knows about RR

I thougt that makers of bicycle tires would have experimentally or
scientifically based knowledge as a foundation of their production.
Therefore I directed my question about rolling resistance to Continental
Tires
- and the production manager kindly sent me a reply that is surprisning as
well as interesing.
The question was:

It has been experimentally established that a 25 mm tire produces less
rolling resistance than a 23 mm tire of the same model, and with identical
pressure.
But how does a comparison between the two tires i.e. 25 and 23 mm - each
with the recommended pressure (6,5 bar resp. 7.5 bar) come out?

This will be the relevant comparison if you give SPEED priority to comfort
and tracking.
Nobody in this newsgroup of bicycle connoisseurs had been able to deliver
an answer to my question, but a few indicated, that the difference in RR
between the two tires would be very small and the answer thus unimportant.

That did not satisfy my curiousity however, so I sent the question to
Continental Tires - since it is their 4-Seasons 25 mm I have chosen for my
long distance speed riding.
Here is Continental's quick and kind reply:

"The discussion about the differences in rolling resistance between
23-25mm tires is somewhat theoretical.

Practically you recognize the better damping and cornering characteristics
of the 25mm tire.

By experience I can tell you that you won´t be any slower with a 25mm tire
but have a more enjoyable ride if you prefer to go on backroads or even
try some field roads.

Wolf vorm Walde
Product Manager Bicycle Tires"

Thank you for that opinion. I will still be looking for facts.
I trust, that if mr Walde knew of ane measurable difference, he would be
willing to tell me about it. Therefore he and Continental Tires don't know
of a difference. And if they don't know, most likely nobody knows. I find
that surprising and interesting.

It is obvious that if you give priority to comfort and tracking, you
should prefer af 25 mm to a 23 mm.

But even if you give priority to speed, the 25 mm tire appears to be the
better choice. But nobody knows.

Here is an uncovered field for an engineer student or for a bicycle
magazine to look in to.

Ivar of Denmark

gnaw. what he said was-
"we are unable or willing to commit ourselves or Conti or any dinero to
a quantifiable statement comparing 23mm to 25mm"
but "from the seat of our pants, we can tell you flkat out that 25mm is
better for the average rider than 23mm"

hey-you guys speak german!

On Wed, 15 Jun 2005 00:21:55 +0200, "Ivar Hesselager"
wrote:

I thougt that makers of bicycle tires would have experimentally or
scientifically based knowledge as a foundation of their production.
Therefore I directed my question about rolling resistance to Continental
Tires
- and the production manager kindly sent me a reply that is surprisning as
well as interesing.
The question was:

It has been experimentally established that a 25 mm tire produces less
rolling resistance than a 23 mm tire of the same model, and with identical
pressure.
But how does a comparison between the two tires i.e. 25 and 23 mm - each
with the recommended pressure (6,5 bar resp. 7.5 bar) come out?

This will be the relevant comparison if you give SPEED priority to comfort
and tracking.
Nobody in this newsgroup of bicycle connoisseurs had been able to deliver
an answer to my question, but a few indicated, that the difference in RR
between the two tires would be very small and the answer thus unimportant.

That did not satisfy my curiousity however, so I sent the question to
Continental Tires - since it is their 4-Seasons 25 mm I have chosen for my
long distance speed riding.
Here is Continental's quick and kind reply:

"The discussion about the differences in rolling resistance between
23-25mm tires is somewhat theoretical.

Practically you recognize the better damping and cornering characteristics
of the 25mm tire.

By experience I can tell you that you won´t be any slower with a 25mm tire
but have a more enjoyable ride if you prefer to go on backroads or even
try some field roads.

Wolf vorm Walde
Product Manager Bicycle Tires"

Thank you for that opinion. I will still be looking for facts.
I trust, that if mr Walde knew of ane measurable difference, he would be
willing to tell me about it. Therefore he and Continental Tires don't know
of a difference. And if they don't know, most likely nobody knows. I find
that surprising and interesting.

It is obvious that if you give priority to comfort and tracking, you
should prefer af 25 mm to a 23 mm.

But even if you give priority to speed, the 25 mm tire appears to be the
better choice. But nobody knows.

Here is an uncovered field for an engineer student or for a bicycle
magazine to look in to.

Ivar of Denmark

Dear Ivar,

I suspect that most people who ponder the matter will find
it fascinating theoretically, but will also discover that
there's very little practical speed difference.

For one thing, when extrapolated to speeds where small
advantages matter, there just isn't much difference when the
tires are of roughly the same construction.

That is, the difference between a 23mm and a 25mm racing
clincher is not as dramatic as the difference between an MTB
tire with huge knobs and a slick--and some of the knobby's
slowness is due to hideous aerodynamics, not rolling
resistance.

Speaking of aerodynamics, the trouble with a wider tire's
slightly lower rolling resistance is its increased wind
drag.

At some speed, the roughly 10% increase in frontal area on
the front and back halves of each tire will increase wind
drag enough to offset the tiny rolling resistance gain.

Given a pair of tires roughly 680 mm high, a 2mm increase in
width suggests an increase of 1,360mm^2, four times, or
5,440mm^2 extra tire surface trying to move through the air,
or about 8.4 square inches of increased frontal area.

This doesn't sound like much, only about the equivalent of
sticking your fist into the air. But even a little extra
wind drag makes a bigger and bigger difference as speed
increases, while rolling resistance only increases steadily.

http://w3.iac.net/~curta/bp/velocityN/velocity.html

Using the calculator above (the metric version offers
rolling resistance and frontal area), let's try a few values
and see what we get.

The default values predict a brisk 37.18 km/h.

Reduce the rolling resistance 5% from 0.0050 to 0.0045, and
the speed rises to 37.40 km/h, an increase of 0.22 km/h.

But if that 5% reduction in rolling resistance also
increased the frontal area from 0.4m^2 to 0.40544m^2, then
the speed drops to 37.24 km/h.

So the combination of a wider tire that rolls more easily is
predicted to increase a rider's speed only 0.06 km/h, or
sixty meters in an hour--a convenient 1 meter per minute.

An advantage that enables you to pull less than a bike
length ahead of another rider in one minute is probably not
worth a lot of practical research, even though you and I
enjoy speculating about it.

Reduce the watts from the impressive default 300 to a more
modest 150 watts, and the base speed is predicted to be
28.48 km/h, the pure rolling resistance reduced 5% raises
the speed to 28.76 km/h, and the final speed with the wider
tire's wind drag added drops back to 28.64 km/h--about 0.16
km/h faster, so rolling resistance does indeed matter more
at lower speeds, where wind drag isn't so important. It's
conveniently about 0.1 mph, or about nine extra feet per
minute at around 18 mph.

Carl Fogel

Ivar Hesselager wrote:

I thougt that makers of bicycle tires would have experimentally or
scientifically based knowledge as a foundation of their production.


I understand your concern.

Not long ago, I spent an hour in the bookstore reading pieces of
technology in :

Bicycling Science : Third Edition
by David Gordon Wilson

and I was somwehat disappointed in the section on Rolling Resistance.

Not necessarily by Wilson's presentation, but by what he indicated was
only a modest theoretical basis with little experimental verification.

Because of the greater dollar and sales volume and greater consumption,
there may be a better technology basis in Automotive Tires. At least,
in the late 1960's tire companies were out hiring brand new PhD
graduates from my engineering school.

On the other hand, the confirming data and experiments may be company
proprietary, and unpublished.

Sad.

If you can get this book, you might form a similar conclusion. Well, you
already have formed a conclusion.

Jim Buch

Ivar Hesselager wrote:

It is obvious that if you give priority to comfort and tracking, you
should prefer af 25 mm to a 23 mm.

And why not 28 mm to 25 mm while you're at it...

But even if you give priority to speed, the 25 mm tire appears to be the
better choice. But nobody knows.

I don't think anybody has questioned the fact that the higher the
pressure, the lower the rolling resistance. Narrower tyres can handle
higher pressures while causing less stress for the rim. If you want
pressures higher than what 25 mm tyres can take you must use a narrower
tyre.

I always pump my 23 mm tyres pretty hard. 9 bar in the rear and 8 in
the front feel pretty good. As a lightweight rider (70 kg including the
bike) I absolutely don't need such high pressures, but then it doesn't
bother me at all and I can ride my usual mileage without any discomfort.
Even if the increase in rolling resistance might be very small, it
doesn't seem like a bad deal to me.

-as

Quoting Ivar Hesselager :
But how does a comparison between the two tires i.e. 25 and 23 mm - each
with the recommended pressure (6,5 bar resp. 7.5 bar) come out?
This will be the relevant comparison if you give SPEED priority to comfort
and tracking.

No, it's not. If you want to maximise speed, you should use in both tyres
the maximum pressure that does not cause the increase in RR we see with
track-style pressures (eg 170psi), or the maximum pressure that does not
produce an intolerably hard ride; that will be equal in both cases and
the 25mm tyre will have lower RR.

Why would you use a lower pressure in the 25mm tyre if the aim is to
maximise speed?

Nobody in this newsgroup of bicycle connoisseurs had been able to deliver
an answer to my question,

But you did get a perfectly good explanation of why it is not a sensible
question to ask.
--
David Damerell flcl?
Today is Second Brieday, June.

Ivar Hesselager wrote:
I thougt that makers of bicycle tires would have experimentally or
scientifically based knowledge as a foundation of their production.
Therefore I directed my question about rolling resistance to
Continental Tires
- and the production manager kindly sent me a reply that is surprisning
as well as interesing.
The question was:

It has been experimentally established that a 25 mm tire produces less
rolling resistance than a 23 mm tire of the same model, and with
identical pressure.
But how does a comparison between the two tires i.e. 25 and 23 mm -
each with the recommended pressure (6,5 bar resp. 7.5 bar) come out?

This will be the relevant comparison if you give SPEED priority to
comfort and tracking.
Nobody in this newsgroup of bicycle connoisseurs had been able to
deliver an answer to my question, but a few indicated, that the
difference in RR between the two tires would be very small and the
answer thus unimportant.

That did not satisfy my curiousity however, so I sent the question to
Continental Tires - since it is their 4-Seasons 25 mm I have chosen for
my long distance speed riding.
Here is Continental's quick and kind reply:

"The discussion about the differences in rolling resistance between
23-25mm tires is somewhat theoretical.

Practically you recognize the better damping and cornering
characteristics of the 25mm tire.

By experience I can tell you that you won´t be any slower with a 25mm
tire but have a more enjoyable ride if you prefer to go on backroads or
even try some field roads.

Wolf vorm Walde
Product Manager Bicycle Tires"

Thank you for that opinion. I will still be looking for facts.
I trust, that if mr Walde knew of ane measurable difference, he would
be willing to tell me about it. Therefore he and Continental Tires
don't know of a difference. And if they don't know, most likely nobody
knows. I find that surprising and interesting.

It is obvious that if you give priority to comfort and tracking, you
should prefer af 25 mm to a 23 mm.

But even if you give priority to speed, the 25 mm tire appears to be
the better choice. But nobody knows.

Here is an uncovered field for an engineer student or for a bicycle
magazine to look in to.

Ivar of Denmark







Continental have a star rating for rolling resistance here.

http://www.conti-tyres.co.uk/conticy...pplication.pdf

Whilst it's only a rough guide it indicates they've made some effort to
investigate the matter.

Marty

Ivar Hesselager wrote:
"The discussion about the differences in rolling resistance between
23-25mm tires is somewhat theoretical.

Practically you recognize the better damping and cornering characteristics
of the 25mm tire.

By experience I can tell you that you won´t be any slower with a 25mm tire
but have a more enjoyable ride if you prefer to go on backroads or even
try some field roads.

Wolf vorm Walde
Product Manager Bicycle Tires"

Thank you for that opinion. I will still be looking for facts.
I trust, that if mr Walde knew of ane measurable difference, he would be
willing to tell me about it. Therefore he and Continental Tires don't know
of a difference. And if they don't know, most likely nobody knows. I find
that surprising and interesting.

That's not my interpretation of his response, but you could be right.
My take on it is that he's saying it's complicated, that multiple
variables play into rolling resistance, but that you will have a more
comfortable ride with no loss of speed if you are riding on relatively
rough pavement.

I cannot believe that Conti does not have a setup for getting some
measurement of RR for its bicycle tires. Whatever number they get, it
might be only meaningful for the exact environmnet- the test setup-
where it was produced. I can understand their reluctance to give a hard
number that would be immediately used by the riding public to draw
conclusions that are often invalid.

It is obvious that if you give priority to comfort and tracking, you
should prefer af 25 mm to a 23 mm.

But even if you give priority to speed, the 25 mm tire appears to be the
better choice. But nobody knows.

I would say it depends on the road surface and speed at which you ride.

Here is an uncovered field for an engineer student or for a bicycle
magazine to look in to.

Could be interesting to see how rolling resistance varies by air
pressure, road surface, tire construction- a lot of variables to deal
with. That's why I think that Conti's answer was more precise than it
might seem at first. He basically boils down the multiple variables to
a meaningful answer: for the conditions he describes, you will be more
comfortable and just as fast with a 25mm tire. There is an implication
that for other conditions the answer could be different.

wrote:

http://w3.iac.net/~curta/bp/velocityN/velocity.html

Using the calculator above (the metric version offers
rolling resistance and frontal area), let's try a few values
and see what we get.

The default values predict a brisk 37.18 km/h.

Reduce the rolling resistance 5% from 0.0050 to 0.0045, and
the speed rises to 37.40 km/h, an increase of 0.22 km/h.

But if that 5% reduction in rolling resistance also
increased the frontal area from 0.4m^2 to 0.40544m^2, then
the speed drops to 37.24 km/h.

So the combination of a wider tire that rolls more easily is
predicted to increase a rider's speed only 0.06 km/h, or
sixty meters in an hour--a convenient 1 meter per minute.

I note that for these defaults, the two tires become equal at a little
below 44 km/h. (set the power to 473.5 watts)

(This is assuming no wind and no drafting)

--
Benjamin Lewis

Seeing is deceiving. It's eating that's believing.
-- James Thurber

Antti Salonen wrote:

I always pump my 23 mm tyres pretty hard. 9 bar in the rear and 8 in
the front feel pretty good. As a lightweight rider (70 kg including the
bike) I absolutely don't need such high pressures, but then it doesn't
bother me at all and I can ride my usual mileage without any discomfort.
Even if the increase in rolling resistance might be very small, it
doesn't seem like a bad deal to me.

Depending on the smoothness of the road, you might actually be increasing
your rolling resistance by pumping that high.

--
Benjamin Lewis

Seeing is deceiving. It's eating that's believing.
-- James Thurber