Re: Nobody knows about RR

David Damerell said:

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),

Um, what increase in RR is that?

Quoted message said:

produce an intolerably hard ride; that will be equal in both cases and
the 25mm tyre will have lower RR.

I don't think either of those conclusions are true. For one thing, a 25mm
tire may reach blow-off pressures before it is "intolerably hard", and at
that pressure I would assume the RR of the two sizes would be close to the
same.

--

David L. Johnson

__o | A mathematician is a machine for turning coffee into theorems.
_`\(,_ | -- Paul Erdos
(_)/ (_) |

15 Jun 2005 12:15:01 +0100 (BST), David Damerell
<[email hidden]> skrev:

Quoted message said:

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?

Because overinflated tires are not faster: they jump too much, and have
too little grip.

Depending on the character of the road surface you might gain some speed
by increasing inflation TO A LIMIT. This would be true for 23 as well as
25 mm.
The ideal comparison would be between the two sizes of tires, each with
their ideal pressure (for road quality and rider weight). This should be
reflected in their "recommended pressure" - not in the same pressure.

Quoted message said:

But you did get a perfectly good explanation of why it is not a sensible
question to ask.

I still think the explanation was too much common sence and not as exact
as I want it.

Kind Regards
Ivar

David L. Johnson said:

David Damerell said:

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),

Um, what increase in RR is that?

I haven't seen any data anywhere, but it makes intuitive sense to me that
if the tire is so hard that road bumps significantly increase vibrations in
bike and rider, that this is energy being wasted.

Quoted message said:

Quoted message said:

produce an intolerably hard ride; that will be equal in both cases and
the 25mm tyre will have lower RR.

I don't think either of those conclusions are true. For one thing, a
25mm tire may reach blow-off pressures before it is "intolerably hard",
and at that pressure I would assume the RR of the two sizes would be
close to the same.

Do blow-off pressures vary with tire width? How and why?

--
Benjamin Lewis

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

Benjamin Lewis said:

David L. Johnson said:

David Damerell said:

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),

Um, what increase in RR is that?

I haven't seen any data anywhere, but it makes intuitive sense to me that
if the tire is so hard that road bumps significantly increase vibrations in
bike and rider, that this is energy being wasted.

[snip]

Dear Benjamin,

Like you, I haven't seen actual data about increasing
pressure eventually causing rock-hard tires slow down becaue
they bounce like kangaroos.

But the theory is explained (without marsupials) in Lennard
Zinn's reply to Tom here:

http://www.ottawabicycleclub.ca/phpBB2/viewtopic.php?t=137&

Zinn gaves no details or data, but he did say that he "saw
results" and was "told of similar results":

"Years ago, for example, I saw results like this at the
Continental tire factory. I was told of similar results at a
number of other tire factories I have visited."

Like Ivar, of course, I yearn for oodles of details.

Carl Fogel

Quoting Ivar Hesselager <[email hidden]>:

Quoted message said:

<[email hidden]> skrev:

Quoted message said:

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

Because overinflated tires are not faster: they jump too much, and have
too little grip.

What makes you suppose this limit varies with width?

Quoted message said:

The ideal comparison would be between the two sizes of tires, each with
their ideal pressure (for road quality and rider weight). This should be
reflected in their "recommended pressure" - not in the same pressure.

There cannot be any single recommended or ideal pressure when riders have
different desires vis-a-vis comfort and speed.
--
David Damerell <[email hidden]> flcl?
Today is Second Gouday, June.

16 Jun 2005 15:23:47 +0100 (BST), David Damerell
<[email hidden]> skrev:

Quoted message said:

What makes you suppose this limit varies with width?

Because Sheldon says so, thats why!
Read this:
http://www.sheldonbrown.com/tires.html#pressure

If that doesn't convince you, look at the side of a 23 mm tire and a 25 mm
tire. The max pressure will vary with width, and if there is a recommended
pressure there also, that will vary with width as well.

Quoted message said:

There cannot be any single recommended or ideal pressure when riders have
different desires vis-a-vis comfort and speed.

Right and wrong! We all have to look for our own ideal compromise if we
want to make the intelligent choise of width and the pressure in our
tires based on information about different road quality, different
weights, different preferences concerning comfort, traction and speed.
The ideal pressure that YOU will reach for YOUR tires will be higher for a
23 mm than for a 25 mm.
The recommended pressure is a place to start your personal investigation,
as it is the tire makers compromise for the same factors, but for an
imagined average cyclist, that much I can predict.
So if you want to make the ideal choice of tire width and pressure you
must make an calculation/assumption of which tire and which pressure will
give you the lower RR. Since it is impossible to ask you and me and
everybody else about our experiences and preferences, the practical way to
find the relevant data is to compare RR for the two tire sizes, each with
their recommended pressure. We already know that an overinflated 25 mm
tire has less rolling resistance than a correctly infalted 23 mm tire.
We still need to know the result of a comparisen of two (for an imagninary
average cyclist) correctly inflated tires.

Cheers
Ivar

Quoting Ivar Hesselager <[email hidden]>:

Quoted message said:

<[email hidden]> skrev:

Quoted message said:

What makes you suppose this limit varies with width?

Because Sheldon says so, thats why!
Read this:
http://www.sheldonbrown.com/tires.html#pressure

I have, many times. That does not say that the point at which there is an
increase in RR or loss in traction from overinflation - the limit I am
asking about - varies with width.

[And, even if it did, Sheldon has no more done any research there than you
or I.]

Quoted message said:

If that doesn't convince you, look at the side of a 23 mm tire and a 25 mm
tire. The max pressure will vary with width, and if there is a recommended
pressure there also, that will vary with width as well.

Yes. The maximum pressure, however, is concerned with blowoff, not with
the limit I am asking about.

So, why do you suppose that limit varies with width?

Quoted message said:

Quoted message said:

There cannot be any single recommended or ideal pressure when riders have
different desires vis-a-vis comfort and speed.

Right and wrong!

Not wrong at all. How is that wrong? Manifestly I cannot make a sensible
recommendation to Joe Racer who wants to go as fast as possible and to Bob
Tourist who wants as much comfort as won't give him pinch flats.

Quoted message said:

The ideal pressure that YOU will reach for YOUR tires will be higher for a
23 mm than for a 25 mm.

No, it won't. Not at all. I pump up my tyres as much as doesn't actually
rattle my nuts on bad tarmac, because that way when I forget to do it for
a few weeks I don't get pinch flats. That's the same pressure in both
widths of tyre.

The same would apply to someone who wants to minimise RR without suffering
what is to them unacceptable discomfort. Same pressure never mind the
width.

Quoted message said:

their recommended pressure. We already know that an overinflated 25 mm
tire has less rolling resistance than a correctly infalted 23 mm tire.
We still need to know the result of a comparisen of two (for an imagninary
average cyclist) correctly inflated tires.

This is just returning to the assumption that the manufacturer's
recommended pressure, which we know is basically bogus, is "correct".

If a 23 and 25mm tyre are at the same pressure, the pressure which
produces acceptable rider comfort, and that pressure is nowhere near
the blowoff point, why is one "overinflated" and the other "correctly"
inflated?
--
David Damerell <[email hidden]> flcl?
Today is Second Chedday, June - a weekend.

David Damerell said:

Quoting Ivar Hesselager <[email hidden]>:

Quoted message said:

<[email hidden]> skrev:

Quoted message said:

What makes you suppose this limit varies with width?

http://www.sheldonbrown.com/tires.html#pressure

I have, many times. That does not say that the point at which there is an
increase in RR or loss in traction from overinflation - the limit I am
asking about - varies with width.

It's not a "point" it's a "region." where two curves intersect. Where
in the region is best for you will depend on your priorities. It is not
possible for anybody to specify a "perfect" tire pressure for a given
situation, any more than anybody can tell you what gear ratio you should
choose for a given piece of road.

You need to figure this out for yourself by experimentation.

Quoted message said:

[And, even if it did, Sheldon has no more done any research there than you
or I.]

No less either. Like many cyclists I have a lot of personal experience
riding different tires at different pressures on different surfaces, and
have been able to make some broad generalizations that may well be
useful to beginners, or to those who have been mindlessly following rote
specifications provided by tire makers.

Quoted message said:

Quoted message said:

If that doesn't convince you, look at the side of a 23 mm tire and a 25 mm
tire. The max pressure will vary with width, and if there is a recommended
pressure there also, that will vary with width as well.

This is less than a 10% difference in width, it would not be surprising
that the various attributes of different pressure settings don't clearly
favor one or t'other.

Quoted message said:

Quoted message said:

Quoted message said:

There cannot be any single recommended or ideal pressure when riders have
different desires vis-a-vis comfort and speed.

Right and wrong!

Not wrong at all. How is that wrong? Manifestly I cannot make a sensible
recommendation to Joe Racer who wants to go as fast as possible and to Bob
Tourist who wants as much comfort as won't give him pinch flats.

Quoted message said:

The ideal pressure that YOU will reach for YOUR tires will be higher for a
23 mm than for a 25 mm.

Theoretically this is true

Quoted message said:

No, it won't. Not at all. I pump up my tyres as much as doesn't actually
rattle my nuts on bad tarmac, because that way when I forget to do it for
a few weeks I don't get pinch flats. That's the same pressure in both
widths of tyre.

Considering all of the variables involved, the difference probably gets
lost in the noise.

Quoted message said:

If a 23 and 25mm tyre are at the same pressure, the pressure which
produces acceptable rider comfort, and that pressure is nowhere near
the blowoff point, why is one "overinflated" and the other "correctly"
inflated?

The same pressure _doesn't_ produce the same rider comfort, but the
difference is likely too subtle to evaluate with any precision.

Sheldon "Season To Taste" Brown
+---------------------------------------------------------+
| To be good is noble; but to show others how to be good |
| is nobler and no trouble. --Mark Twain |
+---------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

I think this thread has mainly muddied the water, so to speak.
Rolling resistance in tires arises almost exclusively inside the tire
and not from scrubbing on the road as was commonly believed when
Specialized introduced a raised center ridge tire to reduce road
contact (scrubbing). Those tires had higher RR than smooth ones
having larger contact with the road.

Knowing that RR is caused by hysteretic* losses in the elastomers in
the tire one can readily assess relative RR values by manually flexing
the tire casings in question. The stiffer and thicker they are, the
greater RR. The thicker the inner tube, the greater the RR. If the
tread is thick enough to have tread grooves, then these allow tread
squirm into these voids and cause higher RR. If the tire has knobs,
then these can bulge under load and increase RR.

If two tires are otherwise identical, the larger cross section tire
will have lower RR because it bends less as it contacts the road.
It's not mysterious and it is easily assessed. However, casings with
fibers that do not adhere well to the elastomeric matrix in which they
lie will slip longitudinally and cause an increase in RR. This is the
case with Kevlar that itself is a lossy material.

Unfortunately we don't have many identical tires to make such
comparisons but the Avocet TT and Criterium were identical, only that
the TT had thinner tread, mainly to reduce RR, which it did.

When we see RR tests noting whether the same tube was used in both
tests is important because the tube acts as an internal well attached
"tread" that flexes with the tire. The tube does not move in an
inflated tire,... even with talcum powder.

* hysteretic: rebounds with less force than that with which it was
deformed, a characteristic typical of rubber and derived from
magnetics:

http://www.lassp.cornell.edu/sethna/hysteresis/WhatIsHysteresis.html

[email hidden]

Quoted message said:

I think this thread has mainly muddied the water, so to speak.
Rolling resistance in tires arises almost exclusively inside the tire
and not from scrubbing on the road as was commonly believed when
Specialized introduced a raised center ridge tire to reduce road
contact (scrubbing). Those tires had higher RR than smooth ones
having larger contact with the road.

Knowing that RR is caused by hysteretic* losses in the elastomers in
the tire one can readily assess relative RR values by manually flexing
the tire casings in question. The stiffer and thicker they are, the
greater RR. The thicker the inner tube, the greater the RR. If the
tread is thick enough to have tread grooves, then these allow tread
squirm into these voids and cause higher RR. If the tire has knobs,
then these can bulge under load and increase RR.

If two tires are otherwise identical, the larger cross section tire
will have lower RR because it bends less as it contacts the road.
It's not mysterious and it is easily assessed. However, casings with
fibers that do not adhere well to the elastomeric matrix in which they
lie will slip longitudinally and cause an increase in RR. This is the
case with Kevlar that itself is a lossy material.

Speaking of which, I'd like to see two identical tires but one with
Kevlar and one not, on the rolling resistance graph at
http://www.terrymorse.com/bike/rolres.html The Avocet FasGrip SL and
SLK come to mind. Coincidentally, Jobst, I noticed you are riding the
new Avocet (black sidewall) tires now. How do the compare to the older,
Japanese-made ones? I've noticed more QC problems and defects, such as
poor casing joints and disintegrating (well, badly, deeply cracked) tread.

Quoted message said:

Unfortunately we don't have many identical tires to make such
comparisons but the Avocet TT and Criterium were identical, only that
the TT had thinner tread, mainly to reduce RR, which it did.

When we see RR tests noting whether the same tube was used in both
tests is important because the tube acts as an internal well attached
"tread" that flexes with the tire. The tube does not move in an
inflated tire,... even with talcum powder.

* hysteretic: rebounds with less force than that with which it was
deformed, a characteristic typical of rubber and derived from
magnetics:

http://www.lassp.cornell.edu/sethna/hysteresis/WhatIsHysteresis.html

[email hidden]

Robin Hubert

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

I think this thread has mainly muddied the water,

See you're writing a bunch these days. Reading also ?
--
Sandy
Verneuil-sur-Seine

*******

La vie, c'est comme une bicyclette,
il faut avancer pour ne pas perdre l'équilibre.
-- Einstein, A.

Robin Hubert said:

Quoted message said:

I think this thread has mainly muddied the water, so to speak.
Rolling resistance in tires arises almost exclusively inside the
tire and not from scrubbing on the road as was commonly believed
when Specialized introduced a raised center ridge tire to reduce
road contact (scrubbing). Those tires had higher RR than smooth
ones having larger contact with the road.

Quoted message said:

Quoted message said:

Knowing that RR is caused by hysteretic* losses in the elastomers
in the tire one can readily assess relative RR values by manually
flexing the tire casings in question. The stiffer and thicker they
are, the greater RR. The thicker the inner tube, the greater the
RR. If the tread is thick enough to have tread grooves, then these
allow tread squirm into these voids and cause higher RR. If the
tire has knobs, then these can bulge under load and increase RR.

Quoted message said:

Quoted message said:

If two tires are otherwise identical, the larger cross section tire
will have lower RR because it bends less as it contacts the road.
It's not mysterious and it is easily assessed. However, casings
with fibers that do not adhere well to the elastomeric matrix in
which they lie will slip longitudinally and cause an increase in
RR. This is the case with Kevlar that itself is a lossy material.

Quoted message said:

Speaking of which, I'd like to see two identical tires but one with
Kevlar and one not, on the rolling resistance graph at:

http://www.terrymorse.com/bike/rolres.html

Quoted message said:

The Avocet FasGrip SL and SLK come to mind.

THey are not the same. The K tires have an added Kevlar belt under
the tread, not part of the casing.

Quoted message said:

Coincidentally, Jobst, I noticed you are riding the new Avocet
(black sidewall) tires now. How do the compare to the older,
Japanese-made ones? I've noticed more QC problems and defects, such
as poor casing joints and disintegrating (well, badly, deeply
cracked) tread.

I am not satisfied with these tires but have a bunch of them and will
use them up. After that, I'm not sure what I will use. I also still
have tansidewall ones in store.

Quoted message said:

Quoted message said:

Unfortunately we don't have many identical tires to make such
comparisons but the Avocet TT and Criterium were identical, only
that the TT had thinner tread, mainly to reduce RR, which it did.

Quoted message said:

Quoted message said:

When we see RR tests noting whether the same tube was used in both
tests is important because the tube acts as an internal well
attached "tread" that flexes with the tire. The tube does not move
in an inflated tire,... even with talcum powder.

Quoted message said:

Quoted message said:

* hysteretic: rebounds with less force than that with which it was
deformed, a characteristic typical of rubber and derived from
magnetics:

Quoted message said:

Quoted message said:

http://www.lassp.cornell.edu/sethna/hysteresis/WhatIsHysteresis.html

[email hidden]

Quoted message said:

I think this thread has mainly muddied the water, so to speak.
Rolling resistance in tires arises almost exclusively inside the tire
and not from scrubbing on the road as was commonly believed when
Specialized introduced a raised center ridge tire to reduce road
contact (scrubbing). Those tires had higher RR than smooth ones
having larger contact with the road.

Knowing that RR is caused by hysteretic* losses in the elastomers in
the tire one can readily assess relative RR values by manually flexing
the tire casings in question. The stiffer and thicker they are, the
greater RR. The thicker the inner tube, the greater the RR. If the
tread is thick enough to have tread grooves, then these allow tread
squirm into these voids and cause higher RR. If the tire has knobs,
then these can bulge under load and increase RR.

If two tires are otherwise identical, the larger cross section tire
will have lower RR because it bends less as it contacts the road.
It's not mysterious and it is easily assessed. However, casings with
fibers that do not adhere well to the elastomeric matrix in which they
lie will slip longitudinally and cause an increase in RR. This is the
case with Kevlar that itself is a lossy material.

Unfortunately we don't have many identical tires to make such
comparisons but the Avocet TT and Criterium were identical, only that
the TT had thinner tread, mainly to reduce RR, which it did.

When we see RR tests noting whether the same tube was used in both
tests is important because the tube acts as an internal well attached
"tread" that flexes with the tire. The tube does not move in an
inflated tire,... even with talcum powder.

* hysteretic: rebounds with less force than that with which it was
deformed, a characteristic typical of rubber and derived from
magnetics:

reading that, one could conclude that you believe rubbers exhibit
ferromagnetism.

the math for mechanical & ferromagnetic hysteresis systems are the same,
but just because you see more reference to one than the other on google
doesn't mean that mechanical hysteresis is a derivative of
ferromagnetic, just as all the other forms of hysteresis are not.

Quoted message said:

http://www.lassp.cornell.edu/sethna/hysteresis/WhatIsHysteresis.html

[email hidden]

Dear Carl:

I actually produced such data when I did my (in)famous Tufo vs.
clinchers
test. Testing different pressures wasn't my goal, so the data is
limited.
I tested the Tufo S3 lites tubulars at 120psi and 145 psi on typical
Oregon chipseal,
using an SRM professional, doing multiple hillclimb trials.

To my surprise, the Tufos required slightly more power at the higher
pressure.
The difference was fairly small -- 2 or 3 watts if I remember right. It
was pretty
close to the margin of error so I didn't make much of it. This was at
low speeds
and it was only the rear wheel. If there is a diff, it would
presumably be greater
at higher speeds. The data is on my other computer and posted at Kraig
Willet's
biketechreview.com site . I might did it up here if anyone's
interested.

-- Jens

On 18 Jun 2005 07:18:24 -0700, "Jens" <[email hidden]>

Quoted message said:

Dear Carl:

I actually produced such data when I did my (in)famous Tufo vs.
clinchers
test. Testing different pressures wasn't my goal, so the data is
limited.
I tested the Tufo S3 lites tubulars at 120psi and 145 psi on typical
Oregon chipseal,
using an SRM professional, doing multiple hillclimb trials.

To my surprise, the Tufos required slightly more power at the higher
pressure.
The difference was fairly small -- 2 or 3 watts if I remember right. It
was pretty
close to the margin of error so I didn't make much of it. This was at
low speeds
and it was only the rear wheel. If there is a diff, it would
presumably be greater
at higher speeds. The data is on my other computer and posted at Kraig
Willet's
biketechreview.com site . I might did it up here if anyone's
interested.

-- Jens

Dear Jens,

I looked around biketechreview.com, but I didn't see any
search function. When I went to your profile, it did offer
to show me the first line or two of all your posts, but I
didn't see the Tufo stuff.

I did find this post about Tufo that mentions you:

http://biketechreview.com/v-web/bulletin/bb/viewtopic.php?t=183

If you can find the post or article, it would be nice to
read it. If there are graphs or anything else hard to cut
and paste into a text post, I'd be glad to host them.

I'm not surprised that you found such a small
difference--most of this kind of stuff is so small that even
controlled testing is difficult, theory is tricky, and the
variability of real world riding obscures it.

Carl Fogel

Quoting <[email hidden]>:

Quoted message said:

If two tires are otherwise identical, the larger cross section tire
will have lower RR because it bends less as it contacts the road.

True. _If_ we don't introduce the distraction mounted here of using a
different pressure in the larger tyre, which is sort of what I have been
driving at.
--
David Damerell <[email hidden]> Kill the tomato!
Today is Teleute, Presuary.

Quoting Sheldon Brown <[email hidden]>:

Quoted message said:

David Damerell said:

Quoting Ivar Hesselager <[email hidden]>:

Quoted message said:

<[email hidden]> skrev:
>What makes you suppose this limit varies with width?
http://www.sheldonbrown.com/tires.html#pressure

I have, many times. That does not say that the point at which there is an
increase in RR or loss in traction from overinflation - the limit I am
asking about - varies with width.

It's not a "point" it's a "region." where two curves intersect.

No; for a given road surface, there is a point at which increased tyre
pressure causes an increase in RR.

"Two curves intersecting" is RR vs. comfort at lower pressure, and that's
true, but that's _not_ what I'm talking about here.

Quoted message said:

Quoted message said:

[And, even if it did, Sheldon has no more done any research there than you
or I.]

No less either. Like many cyclists I have a lot of personal experience
riding different tires at different pressures on different surfaces, and
have been able to make some broad generalizations that may well be
useful to beginners,

I'm not arguing with the content of that Web page. I'm arguing with Ivar
Hesselager, who has introduced it to challenge a specific point it does
not in fact address.

Quoted message said:

Quoted message said:

Quoted message said:

The ideal pressure that YOU will reach for YOUR tires will be higher for a
23 mm than for a 25 mm.

No, it won't. Not at all. I pump up my tyres as much as doesn't actually
rattle my nuts on bad tarmac, because that way when I forget to do it for
a few weeks I don't get pinch flats. That's the same pressure in both
widths of tyre.

Considering all of the variables involved, the difference probably gets
lost in the noise.

The statement above re "ideal pressure" will remain untrue.

Quoted message said:

Quoted message said:

If a 23 and 25mm tyre are at the same pressure, the pressure which
produces acceptable rider comfort, and that pressure is nowhere near
the blowoff point, why is one "overinflated" and the other "correctly"
inflated?

The same pressure _doesn't_ produce the same rider comfort, but the
difference is likely too subtle to evaluate with any precision.

Which tyre do you contend will be more comfortable?

If the wider one, my argument stands; the rider who wants to go as fast as
they can will have a slightly higher pressure in the 25mm at the limit of
acceptable ride comfort, producing a still lower RR.
--
David Damerell <[email hidden]> Kill the tomato!
Today is Teleute, Presuary.

David Damerell said:

Yes. The maximum pressure, however, is concerned with blowoff, not with
the limit I am asking about.

So, why do you suppose that limit varies with width?

Ifn that limit is defined by the shape of the contact patch, it's obvious.
The same contact patch *shape* on a thinner tire requires proportionally
higher pressure (since the contact patch is determined by weight and
pressure). It seems likely to me that it is in fact the case that the
limit depends on the shape of the contact patch since the limit *also*
seems to vary in direct proportion to the weight of the rider/bike combo.

Jasper