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  #81  
Old October 6th 05, 08:31 PM
external usenet poster
 
Posts: n/a
Default Clinchers vs. Sew-ups

wrote:
anonymous snipes:
Don't be a jerk, Brandt. I'm not repeating myth and lore, I'm
stating something that occured to me and threw out for discussion.


Oh? "better shock absorption", "more comfortable ride", "lower
rolling resistance" are classics of pro-tubular speak and no
quantitative values or explanation how these things are achieved.
That is what myth and lore are made of!


What an ass. Proposing a hypothesis for discussion is not the same
as claiming something to be true; quantitative values are not
necessary, and I don't see you providing any, either.


Is it possible to discuss this without using rude epithets? The
response style suggests weakness of your position and lack of
perspective of the concepts involved.


No it doesn't. It applies a deserved label to you for your insulting
habit of insisting that anyone who questions you about anything, is
spouting "myth and lore".

What do you mean by "better shock absorption", "more comfortable
ride", "lower rolling resistance" and how are these produced by, for
instance, glue on the rim. You might notice that outside the
transition of tire casing to rim the two kinds of tire are
mechanically indistinguishable. Both are constrained to not absorb
any road displacements between the rim edges and both have a circular
cross section that can be deformed outside of that diameter. It is
not irrelevant that they are also visibly indistinguishable, exactly
because they are physically identical.


The tire "systems" are not physically identical as anyone can see who
picks them up and looks at them. Clinchers absorb road displacements to
the air inside them beyond the rim edge toward its interior; tubulars
practically do not.

The difference in displacement is hidden inside the casing and the rim.
It is absurd to suggest that they are the same simply because you can't
see the difference.


You say that as though it were a secret or scientific mystery. What
is hidden inside the rim?


Part of the tube, the bead and part of the sidewall?

The problem with your treatise there, in addition to being poorly
written and lacking "quantitative values", is the failure to
demonstrate that the change in pressure is insignificant. You simply
say it is and expect me to take your word for it, which is pretty
much the same method of argument that you always use, and,
ironically, accuse me of using. You present nothing more than lore
that may or may not be myth, but there is no way to know.


I think you don't understand vector forces and how they can be
separated into vertical and horizontal components.


I think I do.

The analysis of
tire casing forces is not a quantitative subject but rather one of
forces and their direction. Tire casings do not support wheels in
compression or bending but purely in tension, similar to wire spokes
in a bicycle wheel.

One thing that I'm pretty sure of is that a tire at 100psi does not
compress as far toward the rim as one at 50psi, so the air pressure
is doing something there that I don't see adequately explained.


Read it again if you missed that. Casing tension varies with pressure
and rim support is given by casing tension.


Or rewrite it so that it is adequately explained.

**** off, Brandt. You don't know how hard I ride.


You just explained that you don't get snake bites. I don't know any
active riders who have never gotten such a flat and I have seen a lot
of them.


I don't remember any circumstance where I had a flat on a tubular that
I could attribute to compression of the tire to the rim, except for
being squeezed once about 25 years ago into a curb by a car. And
despite what you say, there are few people on this ng that ride
tubulars regularly that have that type of flat with any regularity if
at all. It's a stupid argument, regardless, because it's a false
dichotomy: you are probably one of only a handfull of people in the
world that have an opinion on it that would claim
that tubulars and clinchers are equally subject to pinch flats.

So, again, **** off.

The term snake bite was coined at my Wednesday evening tubular
patch sessions in the 1970's when our local racers came to patched
flats.


We all know the lore of how you supposedly coined the phrase- you've
told us over and over again.


This only gets repetition when you do as though you never heard of it
or understand how it occurs.


Which has nothing to do at all with the tall tale about you coining the
phrase.

Do you repair tubular tires?


I think I said no, or at least very infrequently, anymore, below.
However, I have repaired many, many of them. The only tires I remember
as having punctures not attributable to outside punctures were some
steel (that's right, steel) belted Hutchinsons. Because the problem
ONLY occurred with them, and I never bought any more of them, I believe
it was a tire design issue, and at the time thought it was likely that
impacts were causing tube penetration by wires in the steel belts. I
admit it would indicate that with some frequency I do bottom out the
tire, yet I don't get pinch flats with the more conventionally designed
tubulars.

I don't understand what your are proposing here. Are you saying that
these people are not capable of measuring rolling drag?


They measure it indirectly by doing coast-down testing.

Your tests prove what they prove: that with some unknown but
admittedly inferior glue and gluing technique (you implied that the
gluing technique allowed for easy removal to replace a tire after a
flat; and you definitely did not use the best glue available today),
some Avocet clincher demonstrated lower rr than some unknown
tubular, and that that advantage disappeared with the better bond
provided by track shellac.


Those are not unknown tubulars. I think your arguments fall in the
same bag as the denial that disc brakes pose a hazard as they are
designed today.


I have no opinion on disc brakes.

If the tubulars are not unknown, then you should be able to tell us
here the make and model. If you do, I would rephrase my statement
thusly: "that with some unknown but admittedly inferior glue and gluing
technique (you implied that the gluing technique allowed for easy
removal to replace a tire after a flat; and you definitely did not use
the best glue available today), some Avocet clincher demonstrated lower
rr than a (fill in tubular name) tubular that has been out of
production for (fill in number of years out of production) years and
whose performance was not quantified by comparison to other tubulars,
and that that advantage disappeared with the better bond provided by
track shellac."


You seem to believe that tubulars at their peak use had something that
could be improved. Can you explain what those features are and how
they affect performance?


That would be a better question to ask Conti or Vittoria. For me, the
answer is I don't know, but would not be willing to make any
assumptions that nothing could be improved.

Vittoria Mastik One was not around then, from what I can tell.


It has been around as long as Vittoria has been in the tubular business.


Vittoria has had glue but Mastik One? If so, did you use it? If you
didn't, and I'm pretty sure you used Clement, you used a vastly
inferior glue, which goes back to what I already said: you did not
quantify the quality of the glue or the gluing technique.

But 3M should be replaced by Vittoria Mastik One. It has been shown
experimentally to be superior to 3M and every other glue used for
gluing tubulars in all characteristics that seem to be important for a
glue.


In what way is it superior.


Bond strength, heat resistance, time to achieve ridable bond strength.
Go read the test reports. I posted the reference already in this
thread.

Do you not believe that tubulars move on tacky road glue


I don't know whether a tire glued on properly with it would "move"
significantly more than shellac. And neither do you, because you didn't
test it.

and that this
is addressed by using hard glues for timed track events?


Sure. And _maybe_ by using the best glues on the road.

What conclusion do you find faulty and why?


I already answered that.

I have not seen any bond strength comparisons.


That's because you didn't read the reports that I referenced.

Higher bond strength
seems not to be desirable because tires cannot be removed
non-destructively, as you can read from people damaging base tapes
from excessively cured glue.


And which we have now determined was probably because they didn't use
the best technique for removing the tires, prying up a spot on a tire,
working the tool all the way under it, and then working the tool around
the rim. Once you get it going you may be able to pull it the rest of
the way off by hand, but you have to make sure you are pulling up the
base tape, not the casing. It is not that hard, and it is certainly
easier than trying to tear off by hand a tire glued on that well. I
have NEVER damaged a base tape removing a tire.

The question is whether a strong soft glue such as Vittoria Mastik
One, applied properly with the minimal amount necessary to achieve a
secure bond, can approach the performance of shellac, and perhaps
even surpass the performance of shellac in your testing (because the
shellac performance in your testing may not have been optimized).


If it is sticky and elastic it cannot be as low in losses as a
hardened adhesive that is hard to the extent of being brittle, as
shellac is.


Yes, but the difference may not be significant, and unless the shellac
was used with perfect technique (whatever that is) there is always the
possibility that approaching perfect technique with a soft glue could
give better results that you got with the shellac.

These tires were mounted by people who knew their business.


Wasn't their business clinchers?


Their business is tires and tubulars as well. These tests were not
done by desk clerks.


So it wasn't Avocet, who had a major stake in getting clinchers into
the "serious" cycling market? Regardless, it is obvious that they were
dependent on tubular myth and lore as opposed to experimentation in
their glue and their gluing technique.

I don't really see that anymore, but you present a strong argument for
using the minimal amount of glue necessary to provide a strong, secure
bond.


I don't understand what you mean by that. Are you saying that I
propose applying glue in a thick layer before mounting the tire?


On the contrary, I am saying that your research suggests that the best
way to mount a tire is to minimize the thickness of the glue layer
while insuring a strong, secure bond.

As I
said, regardless of who mounted the tire and with which rim glue, base
tapes wore out and rims showed friction wear in the aluminum.


That does not mean that anyone used the best glue or the best
technique.

That's all I ride for the last 30+ years except for a very occasional
mtb excursion. I don't patch them so much anymore, though; I tend to
use Tufo sealant or throw them away. I get very few flats, so this
system works for me without being wasteful.


How very very very few flats? Throwing away a tire that gets a flat,
is wasteful in my perception.


I don't throw away a tire that gets a flat, I try to fix it with Tufo
sealant which usually works. If it doesn't then I am likely to toss it
unless I think it otherwise worth saving. What I am saying is that the
combination of few flats and Tufo rarely leaves me in the position of
having to repair a flat the traditional way.

Please explain what is obsolete.


The glue.


I think if you read wreck.bike.tech you will see that riders still use
the glues furnished by tubular tire manufacturers and these are no
different from those used in the past.


That doesn't mean they are the best.

Just the same, why are you so
fixated on glue? Look at the results.


The glue is significant variable in the results, but unfortunately you
only used two (Clement? & shellac).

Do your base tapes wear in the
course of riding a tire through to the cords or not? I regularly ride
my tires until the cords show, now and in my days on tubulars.


Sadly, I don't. Something else catastrophic usually happens first.

It seems you may also believe most physics is obsolete, much of the
research having been done more than a century ago. Poor Galileo
doesn't rate highly in your science!


And in fact much of it is obsolete, being usable to provide rough
explanations of only phenomena that are directly observable with the
human senses. But, of course, this is really beside the point since
your comment has no purpose other than to belittle and amuse.


I take that as your interpretation of technical explanations of
natural phenomena that disagree with your beliefs.


No, take it as general relativity changed the understanding of gravity
that Galileo and Newton gave us.

Ads
  #83  
Old October 7th 05, 12:02 AM
external usenet poster
 
Posts: n/a
Default Clinchers vs. Sew-ups

anonymous snipes:

Don't be a jerk, Brandt. I'm not repeating myth and lore, I'm
stating something that occured to me and threw out for
discussion.


Oh? "better shock absorption", "more comfortable ride", "lower
rolling resistance" are classics of pro-tubular speak and no
quantitative values or explanation how these things are achieved.
That is what myth and lore are made of!


What an ass. Proposing a hypothesis for discussion is not the same
as claiming something to be true; quantitative values are not
necessary, and I don't see you providing any, either.


Is it possible to discuss this without using rude epithets? The
response style suggests weakness of your position and lack of
perspective of the concepts involved.


No it doesn't. It applies a deserved label to you for your insulting
habit of insisting that anyone who questions you about anything, is
spouting "myth and lore".


What do you mean by "better shock absorption", "more comfortable
ride", "lower rolling resistance" and how are these produced by,
for instance, glue on the rim. You might notice that outside the
transition of tire casing to rim the two kinds of tire are
mechanically indistinguishable. Both are constrained to not absorb
any road displacements between the rim edges and both have a
circular cross section that can be deformed outside of that
diameter. It is not irrelevant that they are also visibly
indistinguishable, exactly because they are physically identical.


The tire "systems" are not physically identical as anyone can see
who picks them up and looks at them. Clinchers absorb road
displacements to the air inside them beyond the rim edge toward its
interior; tubulars practically do not.


You make obvious that you do not understand how tires support loads.
Has it occurred to you that automotive tire shops mount tires on
wheels, inflate them and subsequently put them in place to support the
car. You cannot see the difference in pressure on a tire pressure
gauge. That is why you can inflate your spare in a car to 30psi to be
subsequently used at 30psi when you let the car off the jack.

The difference in displacement is hidden inside the casing and the
rim. It is absurd to suggest that they are the same simply
because you can't see the difference.


You say that as though it were a secret or scientific mystery.
What is hidden inside the rim?


Part of the tube, the bead and part of the sidewall?


Yes, and what effect does that have on the parameter you claim are
different between clinchers and tubulars?

The problem with your treatise there, in addition to being poorly
written and lacking "quantitative values", is the failure to
demonstrate that the change in pressure is insignificant. You
simply say it is and expect me to take your word for it, which is
pretty much the same method of argument that you always use, and,
ironically, accuse me of using. You present nothing more than
lore that may or may not be myth, but there is no way to know.


I think you don't understand vector forces and how they can be
separated into vertical and horizontal components.


I think I do.


Please demonstrate that rather than dodging with quips.

The analysis of tire casing forces is not a quantitative subject
but rather one of forces and their direction. Tire casings do not
support wheels in compression or bending but purely in tension,
similar to wire spokes in a bicycle wheel.


One thing that I'm pretty sure of is that a tire at 100psi does
not compress as far toward the rim as one at 50psi, so the air
pressure is doing something there that I don't see adequately
explained.


Read it again if you missed that. Casing tension varies with
pressure and rim support is given by casing tension.


Or rewrite it so that it is adequately explained.


You seem to be the exception when it comes to understanding what keeps
a wheel off the ground. I don't believe it needs a rewrite
considering how many people understand what it says. If you start
with incorrect beliefs and hold to them, you will have difficulty
understanding.

**** off, Brandt. You don't know how hard I ride.


You just explained that you don't get snake bites. I don't know
any active riders who have never gotten such a flat and I have seen
a lot of them.


I don't remember any circumstance where I had a flat on a tubular that
I could attribute to compression of the tire to the rim, except for
being squeezed once about 25 years ago into a curb by a car. And
despite what you say, there are few people on this ng that ride
tubulars regularly that have that type of flat with any regularity if
at all. It's a stupid argument, regardless, because it's a false
dichotomy: you are probably one of only a handfull of people in the
world that have an opinion on it that would claim
that tubulars and clinchers are equally subject to pinch flats.


That arises today because most of the tubular riders don't ride
unpaved roads and never get to cobbled streets. As I said, there were
no other tires but tubulars for the sport so we rode them wherever we
went and in those days many of the great roads in the Alps were yet
unpaved. I don't know anyone who rides tubulars today other than at
old timers meets where we try to pull out stuff from the old days.

So, again, **** off.


I see you can't control your emotions. Try to be civil if you want
your utterances to be taken seriously.

The term snake bite was coined at my Wednesday evening tubular
patch sessions in the 1970's when our local racers came to
patched flats.


We all know the lore of how you supposedly coined the phrase-
you've told us over and over again.


This only gets repetition when you do as though you never heard of it
or understand how it occurs.


Which has nothing to do at all with the tall tale about you coining the
phrase.


You seem to have problems with that.

Do you repair tubular tires?


I think I said no, or at least very infrequently, anymore, below.
However, I have repaired many, many of them. The only tires I
remember as having punctures not attributable to outside punctures
were some steel (that's right, steel) belted Hutchinsons. Because
the problem ONLY occurred with them, and I never bought any more of
them, I believe it was a tire design issue, and at the time thought
it was likely that impacts were causing tube penetration by wires in
the steel belts. I admit it would indicate that with some frequency
I do bottom out the tire, yet I don't get pinch flats with the more
conventionally designed tubulars.


I don't understand what your are proposing here. Are you saying
that these people are not capable of measuring rolling drag?


They measure it indirectly by doing coast-down testing.


As I pointed out, that doesn't give the same information direct drag
measurements as a range of inflation pressures do. There is no way
you can see what effect inflation pressure has on RR unless it is
measured over a range of pressures.

Your tests prove what they prove: that with some unknown but
admittedly inferior glue and gluing technique (you implied that
the gluing technique allowed for easy removal to replace a tire
after a flat; and you definitely did not use the best glue
available today), some Avocet clincher demonstrated lower rr than
some unknown tubular, and that that advantage disappeared with the
better bond provided by track shellac.


Those are not unknown tubulars. I think your arguments fall in the
same bag as the denial that disc brakes pose a hazard as they are
designed today.


I have no opinion on disc brakes.


If the tubulars are not unknown, then you should be able to tell us
here the make and model. If you do, I would rephrase my statement
thusly: "that with some unknown but admittedly inferior glue and
gluing technique (you implied that the gluing technique allowed for
easy removal to replace a tire after a flat; and you definitely did
not use the best glue available today), some Avocet clincher
demonstrated lower rr than a (fill in tubular name) tubular that has
been out of production for (fill in number of years out of
production) years and whose performance was not quantified by
comparison to other tubulars, and that that advantage disappeared
with the better bond provided by track shellac."


I take it you haven't looked at the data because the tires are all
identified on the graph:

http://skyscrapercity.com/showthread.php?t=252897

In light of this, I don't understand what your are writing about, not
having looked at the graphs that show the tubular offset due to rim
losses. The curves clearly show a family of similar curves in which
tubulars have the best characteristics (slope of curve and flatness)
but are out of place by a constant. These curves are closely related
most of them being identical except for a bas multiplier.

You seem to believe that tubulars at their peak use had something
that could be improved. Can you explain what those features are
and how they affect performance?


That would be a better question to ask Conti or Vittoria. For me,
the answer is I don't know, but would not be willing to make any
assumptions that nothing could be improved.


You ought to be able to give an answer to that when you have been
arguing that case all along by saying that the test values are
irrelevant because they were made by older tires.

Vittoria Mastik One was not around then, from what I can tell.


It has been around as long as Vittoria has been in the tubular
business.


Vittoria has had glue but Mastik One? If so, did you use it? If
you didn't, and I'm pretty sure you used Clement, you used a vastly
inferior glue, which goes back to what I already said: you did not
quantify the quality of the glue or the gluing technique.


I used Tubasti and Pastali, Clement and Pirelli being a lower
temperature glue that tended to dry out in time.

But 3M should be replaced by Vittoria Mastik One. It has been
shown experimentally to be superior to 3M and every other glue
used for gluing tubulars in all characteristics that seem to be
important for a glue.


In what way is it superior.


Bond strength, heat resistance, time to achieve ridable bond
strength. Go read the test reports. I posted the reference already
in this thread.


Do you not believe that tubulars move on tacky road glue


I don't know whether a tire glued on properly with it would "move"
significantly more than shellac. And neither do you, because you
didn't test it.


You seem to base your disagreement on the use of Vittoria Glue. Is
that the only thing you think is germane in this discussion. Is it
that the whole subject depends on whether or not the tests were done
with this glue? You'll notice that other adhesives are used by the
tubular users in this forum. Do you think they have no reasons for
doing so?

and that this is addressed by using hard glues for timed track
events?


Sure. And _maybe_ by using the best glues on the road.


So if this is not a problem with tubulars, how do you justify the
search for the ideal glue, one that is almost inseparable from the
tire and rim yet one that allows changing a tire. This indicates to
me that there is a problem with gluing them to rims that is worth
addressing.

What conclusion do you find faulty and why?


I already answered that.


Repetition wouldn't hurt. I don't recall you giving an answer on that
anyway, most of which is in this thread right now.

I have not seen any bond strength comparisons.


That's because you didn't read the reports that I referenced.


Higher bond strength seems not to be desirable because tires cannot
be removed non-destructively, as you can read from people damaging
base tapes from excessively cured glue.


And which we have now determined was probably because they didn't
use the best technique for removing the tires, prying up a spot on a
tire, working the tool all the way under it, and then working the
tool around the rim. Once you get it going you may be able to pull
it the rest of the way off by hand, but you have to make sure you
are pulling up the base tape, not the casing. It is not that hard,
and it is certainly easier than trying to tear off by hand a tire
glued on that well. I have NEVER damaged a base tape removing a
tire.


This sounds arduous. You may recall that quick and easy tire changes
is one of the main advantages touted for tubulars.

The question is whether a strong soft glue such as Vittoria Mastik
One, applied properly with the minimal amount necessary to achieve
a secure bond, can approach the performance of shellac, and
perhaps even surpass the performance of shellac in your testing
(because the shellac performance in your testing may not have been
optimized).


If it is sticky and elastic it cannot be as low in losses as a
hardened adhesive that is hard to the extent of being brittle, as
shellac is.


Yes, but the difference may not be significant, and unless the
shellac was used with perfect technique (whatever that is) there is
always the possibility that approaching perfect technique with a
soft glue could give better results that you got with the shellac.


"MAY NOT". I think you'll have to give more evidence than that. I
showed you my data, you show me yours.

These tires were mounted by people who knew their business.


Wasn't their business clinchers?


Their business is tires and tubulars as well. These tests were not
done by desk clerks.


So it wasn't Avocet, who had a major stake in getting clinchers into
the "serious" cycling market? Regardless, it is obvious that they were
dependent on tubular myth and lore as opposed to experimentation in
their glue and their gluing technique.


These tests were performed in Japan by IRC at the time they sponsored
racing and served racing teams.

I don't really see that anymore, but you present a strong argument
for using the minimal amount of glue necessary to provide a
strong, secure bond.


I don't understand what you mean by that. Are you saying that I
propose applying glue in a thick layer before mounting the tire?


On the contrary, I am saying that your research suggests that the
best way to mount a tire is to minimize the thickness of the glue
layer while insuring a strong, secure bond.


Yes, go on, and what does that have to do with the rolling resistance
cause by the interface between tire and rim. As I pointed out, rims
show base tape pattern in the aluminum from this motion. That means
that upon heating from braking, the glue migrates out of the highest
pressure contact and allows the fabric of the tire to contact the
metal. Is that thin enough?

As I said, regardless of who mounted the tire and with which rim
glue, base tapes wore out and rims showed friction wear in the
aluminum.


That does not mean that anyone used the best glue or the best
technique.


You are retreating. The contention is that tubulars mounted on
pressure sensitive (tacky) glue have losses. Now you are saying that
users are not using your preferred adhesive so the concept is flawed.
If you use hardening glue, then there is no rim glue loss. So what?
The point is that tubulars glued with the conventional adhesives have
rolling losses that make them poorer in RR than the best clinchers.

That's all I ride for the last 30+ years except for a very
occasional mtb excursion. I don't patch them so much anymore,
though; I tend to use Tufo sealant or throw them away. I get very
few flats, so this system works for me without being wasteful.
How very very very few flats? Throwing away a tire that gets a
flat, is wasteful in my perception.


I don't throw away a tire that gets a flat, I try to fix it with Tufo
sealant which usually works. If it doesn't then I am likely to toss it
unless I think it otherwise worth saving. What I am saying is that the
combination of few flats and Tufo rarely leaves me in the position of
having to repair a flat the traditional way.


Please explain what is obsolete.


The glue.


I think if you read wreck.bike.tech you will see that riders still
use the glues furnished by tubular tire manufacturers and these are
no different from those used in the past.


That doesn't mean they are the best.


Just the same, why are you so fixated on glue? Look at the
results.


The glue is significant variable in the results, but unfortunately
you only used two (Clement? & shellac).


I never used shellac. I only pointed out that after seeing the test
results I finally discovered why there is hard glue. You
should realize that until these curves were shown, no one in bicycle
racing or the industry could explain why there was hard glue. All
they said was that rolling a tire on a track was a greater possibility
if hard glue was not used.

Do your base tapes wear in the course of riding a tire through to
the cords or not? I regularly ride my tires until the cords show,
now and in my days on tubulars.


Sadly, I don't. Something else catastrophic usually happens first.


It seems you may also believe most physics is obsolete, much of
the research having been done more than a century ago. Poor
Galileo doesn't rate highly in your science!


And in fact much of it is obsolete, being usable to provide rough
explanations of only phenomena that are directly observable with
the human senses. But, of course, this is really beside the point
since your comment has no purpose other than to belittle and
amuse.


I take that as your interpretation of technical explanations of
natural phenomena that disagree with your beliefs.


No, take it as general relativity changed the understanding of
gravity that Galileo and Newton gave us.


In an interview with one of Einstein's colleagues the old professor
said with irritation "He had no right in publishing his relativity
papers because he didn't do the research." This is not an original
tactic as you can see. Attack the messenger, not the message.

Jobst Brandt

  #84  
Old October 7th 05, 12:36 AM
Michael Press
external usenet poster
 
Posts: n/a
Default Clinchers vs. Sew-ups

In article
.com,
wrote:

The problem with your treatise there, in addition to being poorly
written and lacking "quantitative values", is the failure to
demonstrate that the change in pressure is insignificant. You simply
say it is and expect me to take your word for it, which is pretty much
the same method of argument that you always use, and, ironically,
accuse me of using. You present nothing more than lore that may or may
not be myth, but there is no way to know.


Here is my calculation.

A 700x25 tire has a volume of V = 2(pi)^2 r^2 R = 0.0265
m^3, where r = 0.012 m and R = 0.335 m. The ideal gas
equation gives PV = constant, therefore V dP = -P dV.
For finite but small changes in the volume we can use the
approximation

delta P delta V
------ = - ---------
P V

The relative change in pressure is equal to the negative
of the relative change in volume.

There is a hoary old chestnut among physicists: "Consider
a spherical elephant." I am going to go from a torus to a
sphere to continue my analysis. The radius, a, of the
sphere with the same volume as a 700x25 tire is
a = (4V/(3 pi))^(1/3) = 0.185 m. Suppose the skin of
sphere does not stretch. We flatten one end by a distance
s. The volume of a spherical cap of height s is
(3as^2 + s^3)pi.

So delta P / P = (3as^2 + s^3)pi/V
When s is 1 mm delta P / P = 6.6 x 10^(-6).
When s is 5 mm delta P / P = 1.7 x 10^(-3).
When s is 10 mm delta P / P = 6.7 x 10^(-3).

If the tire is squashed by 1 cm, the pressure change in a
100 psi tire is less than 1 psi.

What is the force required to squash the sphere?
The area of the base of the spherical cap is
pi (a^2-(a-s)^2) P = pi (2as-s^2) P.
For a 7.5 bar = 750000 n/m^2 ti
When s = 0.001 m the force is 870 n, or the weight of 88
kg.
When s = 0.005 m the force is 1370 n, or the weight of 139
kg.

I submit that the flattenings and forces in this analysis
accord with our experience of the same physical quantities
associated with bicycle tires. The differences between the
torus in the real world and the sphere analyzed are small
enough to render the pressure changes in the sphere an
excellent approximation to the pressure changes in a
bicycle tire.

--
Michael Press
  #85  
Old October 7th 05, 04:57 AM
Tom Reingold
external usenet poster
 
Posts: n/a
Default Clinchers vs. Sew-ups

So, again, **** off.


I see you can't control your emotions. Try to be civil if you want
your utterances to be taken seriously.


Jobst, you are rewarding his rudeness with a relatively polite reply.
Worse, you are engaging him in the discussion without any sort of
commitment (from him) to civility. If you don't mind, then fine, but if
you keep rewarding him, you can expect more of the same.

Tom
  #86  
Old October 7th 05, 07:29 AM
external usenet poster
 
Posts: n/a
Default Clinchers vs. Sew-ups

Tom Reingold writes:

So, again, **** off.


I see you can't control your emotions. Try to be civil if you want
your utterances to be taken seriously.


Jobst, you are rewarding his rudeness with a relatively polite
reply. Worse, you are engaging him in the discussion without any
sort of commitment (from him) to civility. If you don't mind, then
fine, but if you keep rewarding him, you can expect more of the
same.


I don't write this stuff to please myself but rather to let readers
know there is another explanation for what I generally call myth and
lore, the stuff without merit that is passed from one generation of
bicyclists to the next. The rude responses do two things, they
generally invoke the myth that needs airing, and they do it in a way
that civilized readers recognize as rude and uninformed of the matter
at hand.

As I said above, the readers that count can tell the difference.
There is only one kind of appropriate reply, regardless of what tone
the critic uses, and that is a civil and polite one. Stooping to use
a similarly rude response is not constructive.

When a subject comes up often enough, I often write a short essay on
it and put it in the FAQ so I don't need to write an explanation.
Sheldon was kind enough to offer a bit of space for that on his web
site:

http://www.sheldonbrown.com/brandt/

Jobst Brandt
  #87  
Old October 7th 05, 10:58 PM
external usenet poster
 
Posts: n/a
Default Clinchers vs. Sew-ups

wrote:
You make obvious that you do not understand how tires support loads.
Has it occurred to you that automotive tire shops mount tires on
wheels, inflate them and subsequently put them in place to support the
car. You cannot see the difference in pressure on a tire pressure
gauge. That is why you can inflate your spare in a car to 30psi to be
subsequently used at 30psi when you let the car off the jack.


From
http://www.sheldonbrown.com/brandt/rim-support.html :
" it takes several strokes of a frame pump to increase the pressure of
a tire from 100 psi to 101"

It takes a very small deflection to raise the pressure in a tubular by
5psi with a floor pump. Yes, a full stroke to pressurize the air to the
level that is already in the tire, but a much smaller amount to raise
it above what it already is. Has anyone actually tried to measure the
volume reduction and corresponding change in pressure of a tire when it
is pushed to the rim?

Let's consider a different question: do you believe that clinchers are
more susceptible to pinch flats than tubulars, yes or no? Why?

Part of the tube, the bead and part of the sidewall?


Yes, and what effect does that have on the parameter you claim are
different between clinchers and tubulars?


I merely answered a question you asked, "What parts of a clincher are
not visible?" I did not claim anything.

I think I do.


Please demonstrate that rather than dodging with quips.


**** off, yet again. I had physics and trig.

It's a stupid argument, regardless, because it's a false
dichotomy: you are probably one of only a handfull of people in the
world that have an opinion on it that would claim
that tubulars and clinchers are equally subject to pinch flats.


That arises today because most of the tubular riders don't ride
unpaved roads and never get to cobbled streets.


So, tubular riders have to ride cobblestones to get pinch flats;
clincher riders get them anywhere if they don't pump their tires up to
120psi.

So, again, **** off.


I see you can't control your emotions. Try to be civil if you want
your utterances to be taken seriously.


No, you don't "see". I'm just responding to the rude, nasty, belittling
manner of your argument that has been repeated over and over again in
responding to me and just about everyone else on this ng. I just take
it out in the open, that's all.

But I'm surprised no one's ever knocked your teeth out. A lot of people
wouldn't tolerate your behavior toward them in person without losing
their temper.

Which has nothing to do at all with the tall tale about you coining the
phrase.


You seem to have problems with that.


No, not at all, I enjoy a fairy tale.

They measure it indirectly by doing coast-down testing.


As I pointed out, that doesn't give the same information direct drag
measurements as a range of inflation pressures do. There is no way
you can see what effect inflation pressure has on RR unless it is
measured over a range of pressures.


However, they are completely adequate to dispute the conclusion that
clinchers are inherently superior to tubulars.

If the tubulars are not unknown, then you should be able to tell us
here the make and model. If you do, I would rephrase my statement
thusly: "that with some unknown but admittedly inferior glue and
gluing technique (you implied that the gluing technique allowed for
easy removal to replace a tire after a flat; and you definitely did
not use the best glue available today), some Avocet clincher
demonstrated lower rr than a (fill in tubular name) tubular that has
been out of production for (fill in number of years out of
production) years and whose performance was not quantified by
comparison to other tubulars, and that that advantage disappeared
with the better bond provided by track shellac."


I take it you haven't looked at the data because the tires are all
identified on the graph:


I take it you didn't read the part where I said your link you
previously posted didn't work. But, okay, like I said, consider my
earlier statement modified.

http://skyscrapercity.com/showthread.php?t=252897


This brings up an interesting thread on the Spanish AVE high-speed
trains.

In light of this, I don't understand what your are writing about, not
having looked at the graphs that show the tubular offset due to rim
losses. The curves clearly show a family of similar curves in which
tubulars have the best characteristics (slope of curve and flatness)
but are out of place by a constant. These curves are closely related
most of them being identical except for a bas multiplier.


I have no doubt that your experiment did reveal a squirm caused by the
glue. My problem is that you leap from there to the grand conclusion
that it must be present on all road tires with all glues under all
circumstances.

You ought to be able to give an answer to that when you have been
arguing that case all along by saying that the test values are
irrelevant because they were made by older tires.


No, I said older glues. _You_ said older tires. It was not until you
brought it up that I even discussed whether the tires might be
obsolete. I don't know whether there is anything that could be done or
has been done to improve the rr qualities of tubular tires.

Do you not believe that tubulars move on tacky road glue


I don't know whether a tire glued on properly with it would "move"
significantly more than shellac. And neither do you, because you
didn't test it.


You seem to base your disagreement on the use of Vittoria Glue.


No, I base it on the fact that you did _not_ use Vittoria glue, and
that you did not document your gluing process or manipulate it as a
variable.

Is
that the only thing you think is germane in this discussion. Is it
that the whole subject depends on whether or not the tests were done
with this glue?


I already enumerated what I considered to be flaws in the design of
your experiment relative to your sweeping conclusions.

You'll notice that other adhesives are used by the
tubular users in this forum. Do you think they have no reasons for
doing so?


Myth and Lore? I think that after you read the test data there is no
good reason to use any other glue, except perhaps availability. The
test data is significant enough to make me seek it out.

Sure. And _maybe_ by using the best glues on the road.


So if this is not a problem with tubulars, how do you justify the
search for the ideal glue, one that is almost inseparable from the
tire and rim yet one that allows changing a tire. This indicates to
me that there is a problem with gluing them to rims that is worth
addressing.


It is definitely an issue. If you use tubulars that are as well glued
as is allowed by Mastik One, you will have to rethink the way you get
the tire off. It is not really any more difficult, just different.

This sounds arduous. You may recall that quick and easy tire changes
is one of the main advantages touted for tubulars.


It's actually not, and I don't find it that much slower, maybe a few
seconds with practice.

Yes, but the difference may not be significant, and unless the
shellac was used with perfect technique (whatever that is) there is
always the possibility that approaching perfect technique with a
soft glue could give better results that you got with the shellac.


"MAY NOT". I think you'll have to give more evidence than that. I
showed you my data, you show me yours.


No, you didn't show me data for this, and that's my point: you use
other data and claim it is this. I am questioning your conclusions, not
claiming that I have proof otherwise.

So it wasn't Avocet, who had a major stake in getting clinchers into
the "serious" cycling market? Regardless, it is obvious that they were
dependent on tubular myth and lore as opposed to experimentation in
their glue and their gluing technique.


These tests were performed in Japan by IRC at the time they sponsored
racing and served racing teams.


I think we all know what their stake was.

On the contrary, I am saying that your research suggests that the
best way to mount a tire is to minimize the thickness of the glue
layer while insuring a strong, secure bond.


Yes, go on, and what does that have to do with the rolling resistance
cause by the interface between tire and rim. As I pointed out, rims
show base tape pattern in the aluminum from this motion. That means
that upon heating from braking, the glue migrates out of the highest
pressure contact and allows the fabric of the tire to contact the
metal. Is that thin enough?


Use a better glue with better heat resistance. Do you want me to tell
you again what that would be?

As I said, regardless of who mounted the tire and with which rim
glue, base tapes wore out and rims showed friction wear in the
aluminum.


That does not mean that anyone used the best glue or the best
technique.


You are retreating.


Hardly.

The contention is that tubulars mounted on
pressure sensitive (tacky) glue have losses. Now you are saying that
users are not using your preferred adhesive so the concept is flawed.


Partly, but what I am saying is that unless you can show that you used
the best glue with the best technique your sweeping condemnation of
tubulars is not justified.

I take that as your interpretation of technical explanations of
natural phenomena that disagree with your beliefs.


No, take it as general relativity changed the understanding of
gravity that Galileo and Newton gave us.


In an interview with one of Einstein's colleagues the old professor
said with irritation "He had no right in publishing his relativity
papers because he didn't do the research." This is not an original
tactic as you can see.


Well, I definitely didn't do the research, either.

Attack the messenger, not the message.


No, it's the message alright: your sweeping condemnation of tubulars
tires based on a very limited set of data using obsolete materials.

  #88  
Old October 11th 05, 04:34 PM
external usenet poster
 
Posts: n/a
Default Clinchers vs. Sew-ups


wrote:

I think you'll find that a 25mm clincher has the same deflection to
bottoming as a 25mm tubular, the only difference are a few 0.001" of
casing thickness and tube thickness difference but then clinchers with
thin latex tube and the same TPI are around and they are
indistinguishable in displacement from tubulars. In fact, it takes a
careful eye to see whether a tire is a tubular or clincher unless
there is rim glue smeared around.

I think you missed what supports a rim off the ground but that can be
corrected at:

http://www.sheldonbrown.com/brandt/rim-support.html

"unit casing tension is equivalent to inflation pressure times the
radius of curvature divided by pi. As the curvature reduces when the
tire bulges out, the casing tension decreases correspondingly. The
inflated tire supports the rim primarily by these two effects."

The casing tension is decreased as the tire bulges out in response to
an external force. The local loss of tension creates a localized
difference in casing tension between that part of the tire and the rest
of it, and the pressure acts on the tire as the outside force is
dissapated to equalize the tension. So the effect of the pressure is
not dependent on some increased pressurization caused be compression of
the tire, but by the difference between atmospheric pressure and the
pressure inside the tire (which is obviously a much larger difference)
acting to restore tension to some state of equilibrium for the tire as
a whole.

Nevertheless, the compressibility of an inflated tire is dependent on
its volume, and two tires of equal "radius" above the rim edge,
pressurized to the same degree, will not be equally compressible if the
volume of one tire is different from the other. It looks to me like the
formula above may be flawed in its use of pi; this would be a
reasonably good approximation for a tubular tire, but less so for a
clincher where the correct value may be something more complex (and
larger), and suggests to me that casing tension may be less in a
clincher compared to a tubular of equal pressure, which would
completely explain the anecdotal but widely reported difference between
clinchers and tubulars in their tendency toward bottoming out.

 




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