Tire-making: bead stress, tire width, math, woe........

On 8/22/2011 6:26 PM, kolldata wrote:
ever ride on Specialized turbo's ?
Spec uses Roebling's old wire.
I have a pair now that I just bought to replace the mondo pros that came
with the bike.
I think I posted here how they were the first folded tires that I can
remember having to use tire spoons to install.
Good tires though.

On Mon, 22 Aug 2011 13:32:01 -0700 (PDT), thirty-six
wrote:

On Aug 22, 9:28*pm, DougC wrote:
On 8/22/2011 1:18 PM, thirty-six wrote:



The wire stiffens the connection with the rim so that the tyre stays
in place. *The wire's strength is of no particular importance, it's
the resistance to bending which is key. *...

I don't know if I believe that.

It would mean that you could take a clincher tire and cut both beads
completely through--and then mount & inflate it and still have it stay
on the rim, with just as much pressure as with the beads uncut.

You would be breaking the beam and so the hold of the tyre is
compromised around the cut. Test it statically. Do not ride it at
speed.

Obviously the beads are placed under great tension in use, since for
~100 years steel was the only material used and in the last several
decades the only other material used has been kevlar (which is also a
high tensile strength material).

The steel wire is used as a beam for the tyre's unfortunate edge. The
tubular tyre does not of course suffer from this liability as the
edges are joined together making the tyre essentially edgeless.


Errr... there is no "beam" involved in tire strength.

The bead reinforcement - i.e., the steel or kevlar cable in this case
- is stressed longitudinally, in reference to the cable, as it is used
to prevent the bead stretching.

Kevlar, by the way, is used because it doesn't stretch, not primarily
because it is a high strength material.

Cheers,

John B.

On Mon, 22 Aug 2011 14:29:17 -0700 (PDT), carl fogel
wrote:

On Aug 22, 2:28*pm, DougC wrote:
On 8/22/2011 1:18 PM, thirty-six wrote:



The wire stiffens the connection with the rim so that the tyre stays
in place. *The wire's strength is of no particular importance, it's
the resistance to bending which is key. *...

I don't know if I believe that.

It would mean that you could take a clincher tire and cut both beads
completely through--and then mount & inflate it and still have it stay
on the rim, with just as much pressure as with the beads uncut.

Obviously the beads are placed under great tension in use, since for
~100 years steel was the only material used and in the last several
decades the only other material used has been kevlar (which is also a
high tensile strength material).

Dear Doug,

Jobst cut tire beads and mounted tires, a test repeated by Damon
Rinard:

http://www.sheldonbrown.com/rinard/tirebead.htm

Cheers,

Carl Fogel

But, he didn't flex the tire with the cut bead cable. Try hitting a
pothole with the cut tires and see whether the tire comes off.

Cheers,

John B.

On Aug 22, 7:37*pm, john B. wrote:
On Mon, 22 Aug 2011 13:32:01 -0700 (PDT), thirty-six





wrote:
On Aug 22, 9:28*pm, DougC wrote:
On 8/22/2011 1:18 PM, thirty-six wrote:

The wire stiffens the connection with the rim so that the tyre stays
in place. *The wire's strength is of no particular importance, it's
the resistance to bending which is key. *...

I don't know if I believe that.

It would mean that you could take a clincher tire and cut both beads
completely through--and then mount & inflate it and still have it stay
on the rim, with just as much pressure as with the beads uncut.

You would be breaking the beam and so the hold of the tyre is
compromised around the cut. * Test it statically. *Do not ride it at
speed.

Obviously the beads are placed under great tension in use, since for
~100 years steel was the only material used and in the last several
decades the only other material used has been kevlar (which is also a
high tensile strength material).

The steel wire is used as a beam for the tyre's unfortunate edge. *The
tubular tyre does not of course suffer from this liability as the
edges are joined together making the tyre essentially edgeless.

Errr... there is no "beam" involved in tire strength.

The bead reinforcement - i.e., the steel or kevlar cable in this case
- is stressed longitudinally, in reference to the cable, as it is used
to prevent the bead stretching.

Everyone seems to want to fully adopt one side or the other in this
"belt v. suspenders" discussion. There should really no problem
accepting that there are two mechanism that can work and they can (and
undoubtedly do) work together.

With NO "hook" at the bead, the bead reinforcement does have to take
on the full responsibility for constraining the forces of air pressure
(and all others) within the tire.

But add a substantial hook and the job of the bead reinforcement
becomes much easier. With a suitable means of securing the tire edge
to the rim (thinking hypothetically) all the way around, the
longitudinal strength/stretch resistance of the bead reinforcement
becomes less important or even unnecessary.

Kevlar, by the way, is used because it doesn't stretch, not primarily
because it is a high strength material.

And very UN-stretchy carbon is also becoming the material of choice.

DR

On Aug 22, 5:57*pm, David Scheidt wrote:
AMuzi wrote:
ougC wrote:

: On 8/22/2011 1:30 PM, DirtRoadie wrote:
:
:
: Just for clarification, when you say "bead strength" or "stress on the
: bead," you seem to be referring to the tensile force on the wire or
: whatever material provides the reinforcement of the bead. Is that
: correct?
:
: Yes that's correct.
: What I'd like to be able to predict is, given a tire's width
: (cross-section area) and knowing an inflation pressure it should reach,
: how much tensile strength do the beads need to have.
:
: * There is also the issue of the security of the interface
: between rim and tire at the bead. Essentially, with a secure enough
: bead "hook," the rim would serve in place of the tire bead.
:
: Not with any modern tire. The only tires that were retained by a
: hook-bead rim were the (cotton) cord-bead tires used previous to 1920 or
: so at the latest.
:
: One image, from 1913-
:http://www.norcom2000.com/users/dcim...ies/recumbent/....
:
:
: I have not found anything written that indicated that the tiny ridges on
: the edges of modern clincher bicycle tires plays any part in keeping
: them on the rim.
:
: * By way of
: further example, a tubular tire requires nothing but the tire itself
: (no extra circumferential reinforcement) to withstand applicable
: pressures.
:
:
: The physics of inflation pressure a tubular tire are considerably
: different than a clincher.
:
:
:

:The bead need not be contiguous to hold a tire to a rim.

:This from Jobst, responding to Terry Morse:

:" Someone (Damon Rinard?) did an experiment to show this by
:cutting
: the bead of a tire in several places, and it still held
ressure
: fine.

:That someone was I and Damon repeated the experiment after
:heated
:debate here on wreck.bike erupted when I pointed out that it is
rimarily the clinch that holds tires on rims. "

:Full text he
:http://yarchive.net/bike/blowouts.html

I note that neither person claimed to have ridden the tire. *Dynamic
forces on the bead are much different from static. *I don't find the
experiment at all convincing. *In fact, considering who's proposed it,
I consider it anti-convincing.

I wouldn't go that far. I find it interesting for what it does
suggest. But by analogy, establishing that a belt will hold ones pants
up does not establish that suspenders CANNOT hold one's pants up.

Some individuals who should know better (not present company) seem to
view everything in terms of mutually exclusive black and white.

DR

David Scheidt wrote:

AMuzi wrote:

:This from Jobst, responding to Terry Morse:

:" Someone (Damon Rinard?) did an experiment to show this by
:cutting
: the bead of a tire in several places, and it still held
ressure
: fine.

:That someone was I and Damon repeated the experiment after
:heated
:debate here on wreck.bike erupted when I pointed out that it is
rimarily the clinch that holds tires on rims. "

:Full text he
:http://yarchive.net/bike/blowouts.html

I note that neither person claimed to have ridden the tire. *Dynamic
forces on the bead are much different from static. *I don't find the
experiment at all convincing. *In fact, considering who's proposed it,
I consider it anti-convincing.

Rather than slagging him, why don't you try it yourself?

For my part, I have noticed that some wire-beaded tires blow off at
70psi from non-hooked rims and others stay on board at 200 psi or more
on hooked rims. That by itself suggests that the hook is doing more
than the wire.

Dynamic forces in this case pale compared to static forces that we
consider normal in this age of high pressure tires.

Chalo

"AMuzi" wrote in message
...
DougC wrote:
On 8/22/2011 1:30 PM, DirtRoadie wrote:


Just for clarification, when you say "bead strength" or "stress on the
bead," you seem to be referring to the tensile force on the wire or
whatever material provides the reinforcement of the bead. Is that
correct?

Yes that's correct.
What I'd like to be able to predict is, given a tire's width
(cross-section area) and knowing an inflation pressure it should reach,
how much tensile strength do the beads need to have.

There is also the issue of the security of the interface
between rim and tire at the bead. Essentially, with a secure enough
bead "hook," the rim would serve in place of the tire bead.

Not with any modern tire. The only tires that were retained by a
hook-bead rim were the (cotton) cord-bead tires used previous to 1920 or
so at the latest.

One image, from 1913-
http://www.norcom2000.com/users/dcim..._rims_k25d.jpg I
have not found anything written that indicated that the tiny ridges on
the edges of modern clincher bicycle tires plays any part in keeping them
on the rim.

By way of
further example, a tubular tire requires nothing but the tire itself
(no extra circumferential reinforcement) to withstand applicable
pressures.


The physics of inflation pressure a tubular tire are considerably
different than a clincher.





The bead need not be contiguous to hold a tire to a rim.

This from Jobst, responding to Terry Morse:

" Someone (Damon Rinard?) did an experiment to show this by cutting
the bead of a tire in several places, and it still held
pressure
fine.

That someone was I and Damon repeated the experiment after heated
debate here on wreck.bike erupted when I pointed out that it is
primarily the clinch that holds tires on rims. "

Full text he
http://yarchive.net/bike/blowouts.html

I don't know about this. That John Forester dude that Jobst is quoting
really doesn't look at all knowledgeable. In the link that Forester tries to
discredit James Green, presumably subject matter expert for opposing
counsel, he shows us his lack of education by holding this up as proof of
Green's lack of education. Sadly for Forester, Green is 100% correct. I
stopped reading at this point.

[[
Q Well, what is a vector? It’s velocity and direction, isn’t it?

A A vector is a thing that has magnitude and direction. A velocity vector
has speed and direction.

Q Because speed is velocity.

A No.

Q Speed is not velocity.

A No.

Q What is speed?

A Speed is rate of change in space.

Q Okay, and what is velocity?

A Velocity is rate of change in a direction. Velocity is the vector.
(October 7, 1993, Pg. 36)

Obviously, any middle school student knows that velocity is delta X over
delta T or change in distance over change in time.

]]

Obviously, Mr. Forester didn't pay attention in middle school.

Chalo wrote:
avid Scheidt wrote:
:
: AMuzi wrote:
:
: :This from Jobst, responding to Terry Morse:
:
: :" Someone (Damon Rinard?) did an experiment to show this by
: :cutting
: : the bead of a tire in several places, and it still held
: ressure
: : fine.
:
: :That someone was I and Damon repeated the experiment after
: :heated
: :debate here on wreck.bike erupted when I pointed out that it is
: rimarily the clinch that holds tires on rims. "
:
: :Full text he
: :http://yarchive.net/bike/blowouts.html
:
: I note that neither person claimed to have ridden the tire. Â*Dynamic
: forces on the bead are much different from static. Â*I don't find the
: experiment at all convincing. Â*In fact, considering who's proposed it,
: I consider it anti-convincing.

:Rather than slagging him, why don't you try it yourself?

Well, for one thing, I've seen the remains of a car that had a bead fail
(the wire rope parted) at speed.

if the bead served no useful purpose, you don't think someone would
sell a tire without one? They could save dozens of grams, even
compared to kevlar.

--
sig 11

On Aug 23, 2:37*am, john B. wrote:
On Mon, 22 Aug 2011 13:32:01 -0700 (PDT), thirty-six



wrote:
On Aug 22, 9:28*pm, DougC wrote:
On 8/22/2011 1:18 PM, thirty-six wrote:

The wire stiffens the connection with the rim so that the tyre stays
in place. *The wire's strength is of no particular importance, it's
the resistance to bending which is key. *...

I don't know if I believe that.

It would mean that you could take a clincher tire and cut both beads
completely through--and then mount & inflate it and still have it stay
on the rim, with just as much pressure as with the beads uncut.

You would be breaking the beam and so the hold of the tyre is
compromised around the cut. * Test it statically. *Do not ride it at
speed.

Obviously the beads are placed under great tension in use, since for
~100 years steel was the only material used and in the last several
decades the only other material used has been kevlar (which is also a
high tensile strength material).

The steel wire is used as a beam for the tyre's unfortunate edge. *The
tubular tyre does not of course suffer from this liability as the
edges are joined together making the tyre essentially edgeless.

Errr... there is no "beam" involved in tire strength.

The bead reinforcement - i.e., the steel or kevlar cable in this case
- is stressed longitudinally, in reference to the cable, as it is used
to prevent the bead stretching.

The rim prevents the tyre's edge from stretching (blowing out) it does
not require assistance from concentric restraint.
The wire simply keeps form for the edge.


Kevlar, by the way, is used because it doesn't stretch, not primarily
because it is a high strength material.

It's used to keep the tyre package small because it can withstand
repeated folding without injury. It's used because it's a wonder
material which helps to sell the product.

On Aug 23, 5:14*am, David Scheidt wrote:
Chalo wrote:
avid Scheidt wrote:

:: AMuzi wrote:

:
: :This from Jobst, responding to Terry Morse:
:
: :" Someone (Damon Rinard?) did an experiment to show this by
: :cutting
: : the bead of a tire in several places, and it still held
: ressure
: : fine.
:
: :That someone was I and Damon repeated the experiment after
: :heated
: :debate here on wreck.bike erupted when I pointed out that it is
: rimarily the clinch that holds tires on rims. "
:
: :Full text he
: :http://yarchive.net/bike/blowouts.html
:
: I note that neither person claimed to have ridden the tire. *Dynamic
: forces on the bead are much different from static. *I don't find the
: experiment at all convincing. *In fact, considering who's proposed it,
: I consider it anti-convincing.

:Rather than slagging him, why don't you try it yourself?

Well, for one thing, I've seen the remains of a car that had a bead fail
(the wire rope parted) at speed. *

if the bead served no useful purpose, you don't think someone would
sell a tire without one? *They could save dozens of grams, even
compared to kevlar.

--
sig 11

The wire prevents the edge of the tyre from twisting w.r.t. the rim.
The bead catches a hooked rim to prevent expansion of the tyre
section. With a correctly matched tyre and rim, either mechanism can
hold the tyre until pressures split the rim. Using both systems
together permits one model of tyre to fit different rim sizes. It is
fashionable to put a wide tyre on a narrow rim. Manufacturers prefer
to sell narrow rims because it saves on raw materials. More forces
are at work than those of physics.