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

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

On 8/22/2011 4:29 PM, carl fogel wrote:
On Aug 22, 2:28 pm, 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



That's wonderful! I never would have guessed.
It still doesn't explain the need for steel or kevlar however.

By my own research, a steel bead costs about one-tenth what a kevlar one
does. If making a folding tire was as simple as cutting slits in a steel
bead, and tension on the bead doesn't hold the tire on, then why didn't
bicycle tire companies just sell them that way?

{,,,I would also note that [in the US] the CSPC rules regarding bicycle
tires require them to remain on the rim while rolling a certain distance
when deflated--so any tire with several inches of slack would still not
be legal for sale,,,}

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



--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

On Aug 22, 2:20*pm, 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/dcimper/assorted/inanities/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.

I was not suggesting that the "secure enough bead hook" exists, just
that a sufficient attachment between rim and tire at the bead would
negate any need for the bead to have independent tensile
(circumferential) strength. Others are describing the same thing in
an actual experiment


* 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.

It was just an example showing that there is no need for the
independent tensile strength of a bead to keep the tire from expanding
radially and blowing off the rim as a result. Not intended to be a
complete analysis of all forces involved

DR

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).


That is not so nowadays. On modern rims, it is the shape of
the interface between tire and rim not bead tension.

Older "straight side" rims are a different matter.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

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



--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

ever ride on Specialized turbo's ?
Spec uses Roebling's old wire.

On Aug 22, 10:44*pm, DougC wrote:
On 8/22/2011 4:29 PM, carl fogel wrote:



On Aug 22, 2:28 pm, *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



That's wonderful! I never would have guessed.
It still doesn't explain the need for steel or kevlar however.

I've explained.

By my own research, a steel bead costs about one-tenth what a kevlar one
does. If making a folding tire was as simple as cutting slits in a steel
bead, and tension on the bead doesn't hold the tire on, then why didn't
bicycle tire companies just sell them that way?

{,,,I would also note that [in the US] the CSPC rules regarding bicycle
tires require them to remain on the rim while rolling a certain distance
when deflated--so any tire with several inches of slack would still not
be legal for sale,,,}

On Aug 22, 11:19*pm, AMuzi wrote:
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).

That is not so nowadays. On modern rims, it is the shape of
the interface between tire and rim not bead tension.

Older "straight side" rims are a different matter.


Fact is, a kevlar beaded tyre will roll off a straight sided rim
unless the tyre and rim are clean and grease free at their juncture
and preferably something sticky is applied. A wipe with petroleum
spirit of a rubber finished bead should suffice to make the bead
sticky enough. This is not a practical long term solution. The bead
rolls off precisely because it is flexible. Shape can be sufficient
to retain the bead until the tyre flats.

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..._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
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.


--
sig 126