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

I'm wondering if it is possible that a rough estimate of necessary bead
strength could be determined for a given size tire. There is info online
about figuring wall strength of hoses and cylinders containing pressure,
but they don't deal with the situation of a tire--where the wall is
interrupted.

I've cut up a couple cheap cruiser tires and seen that for them (about
2.1" wide, with a max pressure of 40 PSI) that each of the beads is a
piece of cable with a total breaking strength of about 300 lbs. I could
just match that (even cheap tire beads very rarely fail at their rated
pressures) but it would be nice to know a rule of thumb when making
different-size tires.

From what I have seen of tires I have on hand, the tire's overall
diameter has very little if anything to do with bead loads. I have a
pair of 1.5" wide Kenda Kwest 100 psi tires in 406mm and 559mm, and both
have the same width casings, and both beads measure right about the same
thickness (.118").

{-I am just measuring on the outside of the tire bead, rubber and all,
but anyway}

I also have a 2.3" 559 Big Apple (60 psi), and it is about 6.5" across
the casing, and the beads of it measure right about .150". The BA beads
feel quite stiffer than the Kwests as well.

So then-

1) assuming they have the same cross-section, a larger-diameter tire
(26") does not seen to need a thicker bead than a smaller-diameter tire
(20")

2) the overall tire pressure does necessitate a stronger bead as the
tire pressure increases, but-

3) the stress on the bead increases with the tire's cross-section more
than it does for the pressure (the BA's pressure is only 60% of the
Kwests, but the BA bead is still considerably thicker)

4) I am also wondering now what difference in rim width would make, as
you can get road 26" rims that are ~25mm wide, as well as cruiser 26"
rims that are 80mm wide. On the 80mm rim, not only does the tire's
internal volume increase, but the portion borne by the beads increases
as well.

Is this a problem that can even be estimated roughly, or would it
require 3-d modeling to figure out? It would seem to be fairly simple,
as the tire casing always expands into a circle (the cross-section of
the tire, that is...).

----------

Also when I went looking for such info online, I ran across a lot of
reports of people trying to use non-tubeless tires on tubeless rims.

It's pretty surprising (to me) how common it is for people to say that
the tubeless setups ride much better, but also how common the problem is
of a tire blowing off a tubeless rim and the bead being permanently
damaged from it (ruining the tire). Usually this seems to be with tires
that are not intended for tubeless use; I've already read that a lot of
tires not specified as tubeless are not warrantied for this purpose.

I've never seen these IRL as the first one came out right as I got rid
of the last MTB I had. I've already read a lot of accounts of it, but if
there's any websites that have a lot of pictures and explanations of the
different rims it'd be interesting to see.

On Aug 22, 5:47*pm, DougC wrote:
I'm wondering if it is possible that a rough estimate of necessary bead
strength could be determined for a given size tire. There is info online
about figuring wall strength of hoses and cylinders containing pressure,
but they don't deal with the situation of a tire--where the wall is
interrupted.

I've cut up a couple cheap cruiser tires and seen that for them (about
2.1" wide, with a max pressure of 40 PSI) that each of the beads is a
piece of cable with a total breaking strength of about 300 lbs. I could
just match that (even cheap tire beads very rarely fail at their rated
pressures) but it would be nice to know a rule of thumb when making
different-size tires.

*From what I have seen of tires I have on hand, the tire's overall
diameter has very little if anything to do with bead loads. I have a
pair of 1.5" wide Kenda Kwest 100 psi tires in 406mm and 559mm, and both
have the same width casings, and both beads measure right about the same
thickness (.118").

{-I am just measuring on the outside of the tire bead, rubber and all,
but anyway}

I also have a 2.3" 559 Big Apple (60 psi), and it is about 6.5" across
the casing, and the beads of it measure right about .150". The BA beads
feel quite stiffer than the Kwests as well.

So then-

1) assuming they have the same cross-section, a larger-diameter tire
(26") does not seen to need a thicker bead than a smaller-diameter tire
(20")

2) the overall tire pressure does necessitate a stronger bead as the
tire pressure increases, but-

3) the stress on the bead increases with the tire's cross-section more
than it does for the pressure (the BA's pressure is only 60% of the
Kwests, but the BA bead is still considerably thicker)

4) I am also wondering now what difference in rim width would make, as
you can get road 26" rims that are ~25mm wide, as well as cruiser 26"
rims that are 80mm wide. On the 80mm rim, not only does the tire's
internal volume increase, but the portion borne by the beads increases
as well.

Is this a problem that can even be estimated roughly, or would it
require 3-d modeling to figure out? It would seem to be fairly simple,
as the tire casing always expands into a circle (the cross-section of
the tire, that is...).

* ----------

Also when I went looking for such info online, I ran across a lot of
reports of people trying to use non-tubeless tires on tubeless rims.

It's pretty surprising (to me) how common it is for people to say that
the tubeless setups ride much better, but also how common the problem is
of a tire blowing off a tubeless rim and the bead being permanently
damaged from it (ruining the tire). Usually this seems to be with tires
that are not intended for tubeless use; I've already read that a lot of
tires not specified as tubeless are not warrantied for this purpose.

I've never seen these IRL as the first one came out right as I got rid
of the last MTB I had. I've already read a lot of accounts of it, but if
there's any websites that have a lot of pictures and explanations of the
different rims it'd be interesting to see.

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. This applies so long as the
gap between the rim's walls is around 0.7 of the tyre section. The
tyre's carcass width of fabric from wire to wire will be just over 3/4
of the circumference of the section size. Steel generally presents
the best material for making the wire because of how slim the bead
ends up. This makes fitting and removing easier for the not so wide
rims. The stiffness of a required bead is related to riders'
expectations as to running pressure, loading, road conditions and
riding style. A conservative approach is best unless you can
realistically mark your tyres as racing tyres. Too flexible a wire
will have the tyre rolling off should it puncture.

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).

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.

On 8/22/2011 3:32 PM, thirty-six wrote:
On Aug 22, 9:28 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.

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.


You need to sort the terminology you're using.

Stiffness = resistance to bending.
Tensile strength = resistance to a longitudinal pulling force.

Bicycle tire beads do not need to be stiff at all, steel is stiff but
[foldable] kevlar is not, and both obviously work.

On Aug 22, 9:55*pm, DougC wrote:
On 8/22/2011 3:32 PM, thirty-six wrote:



On Aug 22, 9:28 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.

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.

You need to sort the terminology you're using.

Stiffness = resistance to bending.
Tensile strength = resistance to a longitudinal pulling force.

Bicycle tire beads do not need to be stiff at all, steel is stiff but
[foldable] kevlar is not, and both obviously work.

I've explained why.

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 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 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 8/22/2011 8:37 PM, john B. wrote:
[...]
Errr... there is no "beam" involved in tire strength.
[...]

Yes, he left the newsgroup about a year ago.

--
Tºm Shermªn - 42.435731°N, 83.985007°W
I am a vehicular cyclist.