Tire puzzler

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

Quoted message said:

Less downward pull is equivalent to upward push. That is the
significance of this subject and why it applies to the spoked wheel
and was first introduce in that regard.

Quoted message said:

The tire casing (and its pull on the rim) can be taken completely
out of the picture. Consider a rim with just the inner tube
installed on it. Slowly pump the tube to say 10 psi and observe how
the rim lifts off the ground as the weight of the bicycle is taken
up by the increased air pressure inside the tube. The tube is not
able to pull on the rim.

You are building an invalid free body diagram. That is why a tubular
tire is a better model for this. A bare inner tube will not have
enough pressure to support a rider but it will work the same way for
lighter loads, say just the bicycle.

The attachment to the rim does not need to be a tire bead. It can be
the point at which the tubular tire base tape rests on the rim and
does not flex while the rest of the tire casing deforms with load. It
is that part of the tire that is important.

# The second is that the side wall tension is reduced. The reduction
# arises from the relationship that 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.

Quoted message said:

So what? The side wall tension can also be taken completely out of
the picture using the solo inner tube example from above; i.e.,
there is no pull on the rim from inner tube side wall tension. If
you need to convince yourself of this, envision a layer of Vaseline
between the tube and rim.

It can't or there would be nothing between the rim and the ground with
any forces in it. The inner tube is only an air seal and does not
contribute.

I was using the solo inner tube example to show that a rim can be held off
the ground without the two effects described in your article, i.e., pulling
on the rim by the tire casing and side wall tension.

Use a tubular tire instead of a solo inner tube in the example if you
prefer. Don't glue it to the rim, in fact use a layer of Vaseline between
the tire and rim. The tire will support a vertical load even though it can't
pull on the rim.

JL

JL said:

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

Quoted message said:

Less downward pull is equivalent to upward push. That is the
significance of this subject and why it applies to the spoked wheel
and was first introduce in that regard.

Quoted message said:

The tire casing (and its pull on the rim) can be taken completely
out of the picture. Consider a rim with just the inner tube
installed on it. Slowly pump the tube to say 10 psi and observe how
the rim lifts off the ground as the weight of the bicycle is taken
up by the increased air pressure inside the tube. The tube is not
able to pull on the rim.

You are building an invalid free body diagram. That is why a tubular
tire is a better model for this. A bare inner tube will not have
enough pressure to support a rider but it will work the same way for
lighter loads, say just the bicycle.

The attachment to the rim does not need to be a tire bead. It can be
the point at which the tubular tire base tape rests on the rim and
does not flex while the rest of the tire casing deforms with load. It
is that part of the tire that is important.

# The second is that the side wall tension is reduced. The reduction
# arises from the relationship that 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.

Quoted message said:

So what? The side wall tension can also be taken completely out of
the picture using the solo inner tube example from above; i.e.,
there is no pull on the rim from inner tube side wall tension. If
you need to convince yourself of this, envision a layer of Vaseline
between the tube and rim.

It can't or there would be nothing between the rim and the ground with
any forces in it. The inner tube is only an air seal and does not
contribute.

I was using the solo inner tube example to show that a rim can be held off
the ground without the two effects described in your article, i.e., pulling
on the rim by the tire casing and side wall tension.

Use a tubular tire instead of a solo inner tube in the example if you
prefer. Don't glue it to the rim, in fact use a layer of Vaseline between
the tire and rim. The tire will support a vertical load even though it can't
pull on the rim.

JL

Dear JL,

The sidewall tension is provided by the constraint of the tubular
tire, which encases the tube.

Without the inelastic tire to constrain it and raise the pressure (and
tension), a thin bicycle inner tube would just lengthen enormously
without gaining much pressure (or tension).

Think of a toy balloon. Its volume expands far more than its pressure
and surface tension increase because the thin rubber is so elastic.

There is some increase in tension in the "sidewall" of the balloon,
enough to support a very small weight.

But if you want something that can support your weight, you have to
constrain the balloon inside something far less elastic to raise the
pressure and "sidewall" tension.

Again, you can demonstrate this by pinching a bicycle inner tube
between your thumb and finger and pumping it up. The tube is so
elastic that it lengthens enormously, bulges only slightly, and
provides so little "sidewall" tension that you can pinch it together
with a thumb and finger, just as you can pinch an elastic balloon
together at any point with very little pressure because the thin,
elastic walls provide scarcely any tension.

Cheers,

Carl Fogel

Quoted message said:

I think that if you actually try to support a normally loaded bicycle
with just an inner tube under the rim, you'll find that it doesn't
work--the elastic tube simply expands wildly elsewhere while remaining
squashed flat under the rim.

I'll tell that to Eddie Merckx next time I see him riding sewups...

--Blair

JL said:

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

Quoted message said:

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

Does this FAQ item not answer your question.

Jobst Brandt

I don't see how the referenced article explains the mechanics of how a load
is actually carried by a pneumatic tire.

The article states:

"Under load, in the ground contact zone, the tire bulges so that two effects
reduce the downward pull (increase the net upward force) of the casing.
First, the most obvious one is that the casing pulls more to the sides than
downward (than it did in its unloaded condition); the second is that the
side wall tension is reduced. The reduction arises from the relationship
that 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."

I'm not sure it's entirely sufficient, either.

About 15 years ago, Marvin Minsky mentioned that he
liked to ask Nobel laureates, "how does a tire work?"
then stand amused watching them try to figure it out.

But then, he used to hang around with Nobel laureates,
and I used to converse with Marvin Minsky.

The world's changed for us all.

Quoted message said:

Here's why the explanation doesn't satisfy the question:

"First, the most obvious one is that the casing pulls more to the sides than
downward (than it did in its unloaded condition)"

The tire casing (and its pull on the rim) can be taken completely out of the
picture. Consider a rim with just the inner tube installed on it. Slowly
pump the tube to say 10 psi and observe how the rim lifts off the ground as
the weight of the bicycle is taken up by the increased air pressure inside
the tube. The tube is not able to pull on the rim.

"the second is that the side wall tension is reduced. The reduction arises
from the relationship that 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."

So what? The side wall tension can also be taken completely out of the
picture using the solo inner tube example from above; i.e., there is no pull
on the rim from inner tube side wall tension. If you need to convince
yourself of this, envision a layer of Vaseline between the tube and rim.

The with-casing and without-casing cases are two different cases.

He redunded.

The wheel is supported by the entire bead of a tire with
a casing that has a bead-and-rim interface. In the case
of tubeless tires, this is the only thing supporting the
wheel.

Once the wheel is married to the tire through the bead
and rim interface, it becomes part of the torus. And
the freaky thing is, in automobile tires, it's entirely
a friction fit. The pressure in the tire pushes the sidewall
out which forces the bead against the metal. The static
coefficient of friction at that normal force is high enough
that almost no tires slip on their rims under even the
strongest acceleration of the vehicle. (One example, sadly,
was the original equipment tires on my Lexus, which didn't
have a good enough friction with the new alloy they chose
for the wheels, so they would slip slightly when I matted
it, which in a GS400 is a decent tug. And when it was
new, I really liked making the road go away. This led to
the need to rebalance the rear wheels every thousand miles.
Lexus has since listed other tire models that fit and
will grip those rims, but for a while my car was a lot
like Ken Griffey Jr.: A superman with glass legs.
But I digress...)

This is different from a solid rim of a certain diameter
sitting inside the donut-hole of a tube that is much larger.
That's a matter of having air pressure under the rim (in
the tube) that is higher than the air pressure over it (which
isn't in contact with the tube). Which is the same as putting
a book on top of a balloon, if you can get it to balance.

Quoted message said:

"The inflated tire supports the rim primarily by these two effects."

While perhaps describing some physical attributes of tire casings under
load, these don't explain the phenomenon of what's actually supporting the
load. In the above example something besides tire casing pull and side wall
tension is holding up the rim. The same mechanics that are at work holding
up the rim in the solo inner tube example come into play in all pneumatic
tires.

The tire and the pressure in it convert the upward force
on the contact patch to a transverse force distributed
around the entire bead and the rim.

But it's not equal at all points on the bead interface.
The imbalance could be as simple as a net upward force
at all points which is equivalent to a differential
radial force that rotates as you go around the rim and a
differential tangential force that rotates 90 degrees out
of phase with the radial force around the rim.

The pressure on the rest of the rim surface (between the
beads) is equal around the rim, because that's how gas
pressures work. Any increase at the bottom is equal to the
increase at the top, unless the system is moving so fast
that the propagation of pressure waves becomes an issue.

--Blair

Quoted message said:

Again, you can demonstrate this by pinching a bicycle inner tube
between your thumb and finger and pumping it up. The tube is so
elastic that it lengthens enormously, bulges only slightly, and
provides so little "sidewall" tension that you can pinch it together
with a thumb and finger, just as you can pinch an elastic balloon
together at any point with very little pressure because the thin,
elastic walls provide scarcely any tension.

Do this at 110 psi.

Go ahead.

--Blair

Blair P. Houghton said:

Quoted message said:

Again, you can demonstrate this by pinching a bicycle inner tube
between your thumb and finger and pumping it up. The tube is so
elastic that it lengthens enormously, bulges only slightly, and
provides so little "sidewall" tension that you can pinch it together
with a thumb and finger, just as you can pinch an elastic balloon
together at any point with very little pressure because the thin,
elastic walls provide scarcely any tension.

Do this at 110 psi.

Go ahead.

--Blair

Let us know what happens when you try to inflate an ordinary
thin-walled bicycle inner-tube to 110 psi, unconstrained by a tire.

Blair P. Houghton said:

Quoted message said:

Again, you can demonstrate this by pinching a bicycle inner tube
between your thumb and finger and pumping it up. The tube is so
elastic that it lengthens enormously, bulges only slightly, and
provides so little "sidewall" tension that you can pinch it together
with a thumb and finger, just as you can pinch an elastic balloon
together at any point with very little pressure because the thin,
elastic walls provide scarcely any tension.

Do this at 110 psi.

Go ahead.

You probably couldn't get a bare tube up to 110 psi. Unconstrained, I'm
guessing it'd blow up long before then.
\\paul

Blair P. Houghton said:

Quoted message said:

I think that if you actually try to support a normally loaded bicycle
with just an inner tube under the rim, you'll find that it doesn't
work--the elastic tube simply expands wildly elsewhere while remaining
squashed flat under the rim.

I'll tell that to Eddie Merckx next time I see him riding sewups...

--Blair

Eddie would probably explain that without the edges of the sew-up tire
sewed together to constrain the tube, it would behave exactly as
predicted.

That's why we ride on tires, not naked inner tubes.

You cannot raise the rim without tension, which is the result of
constraining the air pressure. If the "constraint" is as elastic as
inner tube, there won't be enough pressure or tension.

That's why you can pump up and sit on a soccer ball, whose inelastic
side go into tension and constrain the air, but you cannot sit on a
child's balloon of the same size, since its sides offer little
constraint, negligible tension, and scarcely any air pressure.

Paul Hobson said:

You probably couldn't get a bare tube up to 110 psi. Unconstrained, I'm
guessing it'd blow up long before then.

Well, you COULD get 110psi into the tube, but you'd have to be under
about 260 feet of water. ;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Mark Hickey said:

Paul Hobson said:

You probably couldn't get a bare tube up to 110 psi. Unconstrained, I'm
guessing it'd blow up long before then.

Well, you COULD get 110psi into the tube, but you'd have to be under
about 260 feet of water. ;-)

That's 110psivg. You still couldn't do it 8-).

--
Joe Riel

Quoted message said:

Blair P. Houghton said:

Quoted message said:

I think that if you actually try to support a normally loaded bicycle
with just an inner tube under the rim, you'll find that it doesn't
work--the elastic tube simply expands wildly elsewhere while remaining
squashed flat under the rim.

I'll tell that to Eddie Merckx next time I see him riding sewups...

Eddie would probably explain that without the edges of the sew-up tire
sewed together to constrain the tube, it would behave exactly as
predicted.

That's why we ride on tires, not naked inner tubes.

You cannot raise the rim without tension, which is the result of
constraining the air pressure. If the "constraint" is as elastic as
inner tube, there won't be enough pressure or tension.

Depends on the inner tube. A sewup is just an inner tube
with a butyl inner tube in it, if I put it in a clincher.

It's the glue on sewups that keeps the pressure from
pushing the tire away from the rim at the top when the
bottom is under compression.

Quoted message said:

That's why you can pump up and sit on a soccer ball, whose inelastic
side go into tension and constrain the air, but you cannot sit on a
child's balloon of the same size, since its sides offer little
constraint, negligible tension, and scarcely any air pressure.

You never had a childhood:

http://toys-gifts-store.onlineshoppingday.co.uk/104683.html

--Blair

Quoted message said:

Blair P. Houghton said:

Quoted message said:

Again, you can demonstrate this by pinching a bicycle inner tube
between your thumb and finger and pumping it up. The tube is so
elastic that it lengthens enormously, bulges only slightly, and
provides so little "sidewall" tension that you can pinch it together
with a thumb and finger, just as you can pinch an elastic balloon
together at any point with very little pressure because the thin,
elastic walls provide scarcely any tension.

Do this at 110 psi.

Go ahead.

Let us know what happens when you try to inflate an ordinary
thin-walled bicycle inner-tube

So now you have 40 other qualifications for your
example?

Quoted message said:

to 110 psi, unconstrained by a tire.

I bet I can put a bicycle on it and sit on it and the
rim doesn't crush the tube to the ground.

I bet you can't even hope to get its sides to touch
when you squeeze it with two fingers.

--Blair

Quoted message said:

Thicker-walled inner tubes that are large enough, the kind used in
large truck and tractor tires, provide enough constraint, pressure,
and tension to support your weight and are often used to float down
rivers.

The point here is that you jumped someone's perfectly
good example of a certain demonstration of the lifting
power of a pressurized rubber tube and you won't admit
that your "pinch it" retort doesn't have anything
to do with the problem.

Now you're on about the wall thickness and pretending that
the principles that apply to bicycle tubes aren't the same
that apply to tractor tubes.

Hint: they're exactly the same.

The scales are different, but the effect on a rim
is no different.

This was never about the strength of the rubber,
and you know it.

--Blair

Blair P. Houghton said:

Quoted message said:

Blair P. Houghton said:

<[email hidden]> wrote:
>Again, you can demonstrate this by pinching a bicycle inner tube
>between your thumb and finger and pumping it up. The tube is so
>elastic that it lengthens enormously, bulges only slightly, and
>provides so little "sidewall" tension that you can pinch it together
>with a thumb and finger, just as you can pinch an elastic balloon
>together at any point with very little pressure because the thin,
>elastic walls provide scarcely any tension.

Do this at 110 psi.

Go ahead.

Let us know what happens when you try to inflate an ordinary
thin-walled bicycle inner-tube

So now you have 40 other qualifications for your
example?

His "qualification" is just a clarification - precisely what he meant
originally (and what any reasonable reader would have concluded).

Quoted message said:

Quoted message said:

to 110 psi, unconstrained by a tire.

I bet I can put a bicycle on it and sit on it and the
rim doesn't crush the tube to the ground.

I bet you can't even hope to get its sides to touch
when you squeeze it with two fingers.

Errrrrr, one of us is living in a universe with different physics than
the other, apparently.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Joe Riel said:

Mark Hickey said:

Paul Hobson said:

You probably couldn't get a bare tube up to 110 psi. Unconstrained, I'm
guessing it'd blow up long before then.

Well, you COULD get 110psi into the tube, but you'd have to be under
about 260 feet of water. ;-)

That's 110psivg. You still couldn't do it 8-).

Naaaah, I was using a floor pump on a boat - one with a 260 foot hose.
;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Mark Hickey said:

Blair P. Houghton said:

Quoted message said:

On Wed, 27 Sep 2006 00:50:25 GMT, Blair P. Houghton <[email hidden]> wrote:

> <[email hidden]> wrote:
>>Again, you can demonstrate this by pinching a bicycle inner tube
>>between your thumb and finger and pumping it up. The tube is so
>>elastic that it lengthens enormously, bulges only slightly, and
>>provides so little "sidewall" tension that you can pinch it together
>>with a thumb and finger, just as you can pinch an elastic balloon
>>together at any point with very little pressure because the thin,
>>elastic walls provide scarcely any tension.
>
>Do this at 110 psi.
>
>Go ahead.

Let us know what happens when you try to inflate an ordinary
thin-walled bicycle inner-tube

So now you have 40 other qualifications for your
example?

His "qualification" is just a clarification - precisely what he meant
originally (and what any reasonable reader would have concluded).

We're talking about bicycle wheels, which operate at 110
psi. Playing around with tubes at 1.5 bar is not the same
thing and is therefore not reasonable. Hence I mocked him.

Quoted message said:

Quoted message said:

Quoted message said:

to 110 psi, unconstrained by a tire.

I bet I can put a bicycle on it and sit on it and the
rim doesn't crush the tube to the ground.

I bet you can't even hope to get its sides to touch
when you squeeze it with two fingers.

Errrrrr, one of us is living in a universe with different physics than
the other, apparently.

Air pressure is air pressure, no matter how soft the
rest of the tube is. You're not squishing the sides of
a 110 psi tube together with two fingers. Unless they're
this guy's:

http://www.pudzian.pl/

Then I'd make it even-money.

--Blair

Blair P. Houghton said:

Mark Hickey said:

Blair P. Houghton said:

<[email hidden]> wrote:

>On Wed, 27 Sep 2006 00:50:25 GMT, Blair P. Houghton <[email hidden]> wrote:
>
>
>><[email hidden]> wrote:
>>
>>>Again, you can demonstrate this by pinching a bicycle inner tube
>>>between your thumb and finger and pumping it up. The tube is so
>>>elastic that it lengthens enormously, bulges only slightly, and
>>>provides so little "sidewall" tension that you can pinch it together
>>>with a thumb and finger, just as you can pinch an elastic balloon
>>>together at any point with very little pressure because the thin,
>>>elastic walls provide scarcely any tension.
>>
>>Do this at 110 psi.
>>
>>Go ahead.
>
>Let us know what happens when you try to inflate an ordinary
>thin-walled bicycle inner-tube

So now you have 40 other qualifications for your
example?

His "qualification" is just a clarification - precisely what he meant
originally (and what any reasonable reader would have concluded).

We're talking about bicycle wheels, which operate at 110
psi. Playing around with tubes at 1.5 bar is not the same
thing and is therefore not reasonable. Hence I mocked him.

Quoted message said:

Quoted message said:

>to 110 psi, unconstrained by a tire.

I bet I can put a bicycle on it and sit on it and the
rim doesn't crush the tube to the ground.

I bet you can't even hope to get its sides to touch
when you squeeze it with two fingers.

Errrrrr, one of us is living in a universe with different physics than
the other, apparently.

Air pressure is air pressure, no matter how soft the
rest of the tube is. You're not squishing the sides of
a 110 psi tube together with two fingers.

The question is whether you can get 110psi into an unconstrained normal
bicycle inner tube, or will it stretch too thin before it gets anywhere
near 110psi?

Greg

--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

On Wed, 27 Sep 2006 23:09:24 -0700, "G.T." <[email hidden]>

Quoted message said:

Blair P. Houghton said:

Mark Hickey said:

Blair P. Houghton <[email hidden]> wrote:

><[email hidden]> wrote:
>
>>On Wed, 27 Sep 2006 00:50:25 GMT, Blair P. Houghton <[email hidden]> wrote:
>>
>>
>>><[email hidden]> wrote:
>>>
>>>>Again, you can demonstrate this by pinching a bicycle inner tube
>>>>between your thumb and finger and pumping it up. The tube is so
>>>>elastic that it lengthens enormously, bulges only slightly, and
>>>>provides so little "sidewall" tension that you can pinch it together
>>>>with a thumb and finger, just as you can pinch an elastic balloon
>>>>together at any point with very little pressure because the thin,
>>>>elastic walls provide scarcely any tension.
>>>
>>>Do this at 110 psi.
>>>
>>>Go ahead.
>>
>>Let us know what happens when you try to inflate an ordinary
>>thin-walled bicycle inner-tube
>
>So now you have 40 other qualifications for your
>example?

His "qualification" is just a clarification - precisely what he meant
originally (and what any reasonable reader would have concluded).

We're talking about bicycle wheels, which operate at 110
psi. Playing around with tubes at 1.5 bar is not the same
thing and is therefore not reasonable. Hence I mocked him.

Quoted message said:

>>to 110 psi, unconstrained by a tire.
>
>I bet I can put a bicycle on it and sit on it and the
>rim doesn't crush the tube to the ground.
>
>I bet you can't even hope to get its sides to touch
>when you squeeze it with two fingers.

Errrrrr, one of us is living in a universe with different physics than
the other, apparently.

Air pressure is air pressure, no matter how soft the
rest of the tube is. You're not squishing the sides of
a 110 psi tube together with two fingers.

The question is whether you can get 110psi into an unconstrained normal
bicycle inner tube, or will it stretch too thin before it gets anywhere
near 110psi?

Greg

Dear Greg,

Here's the answer, to quote from elsewhere in this thread:

The 110 psi nonsense is from another poster.

Since no one appears to be willing to perform the simple experiment,
here's a picture of what happens if you try to pump an unconstrained
700c inner tube up:

http://home.comcast.net/~carlfogel/download/212_700c_80_pump_strokes_0_psi_4_feet_wide.jpg
or http://tinyurl.com/n3bxa

After 80 strokes with a large floor pump, the 700c tube has obviously
expanded far beyond the 700c rim. The tape measure indicates a 4-foot
wide circle.

The pump indicator registered 0 psi, but the picture showing that
proves only that the shiny glass over the indicator reflects my
camera's automatic flash amazingly well.

Something as broad and heavy as my size 12 shoe with half my 190 pound
weight on it will easily flatten the inflated tube.

Another way to show how little load can be carried is to simply twist
the tube--it's almost effortless to twist it and constrict the section
between your hands into a tiny knot because there's so little tension
in the sidewall.

Mercifully, the tube did not explode. Instead, it sprang a hissing
leak at a seam, typical behavior for such over-expanded tubes.

Cheers,

Carl Fogel

G.T. said:

The question is whether you can get 110psi into an unconstrained normal
bicycle inner tube, or will it stretch too thin before it gets anywhere
near 110psi?

No, the question is how does a tire work.

A tube that has elasticity at 110 psi would be baloonish,
if you assumed ordinary butyl rubber, but it's
not unreasonable to posit a material that has linear
elasticity from some low pressure to beyond 110 psi.

It would have to start out about as thick as macaroni and
as big around as a dinner plate, and expand to the size
of a bicycle tire.

That material could be used to make a bicycle tire.

Now. Try to squish it with your fingers until they
touch. It won't be much easier than doing it to the
110 psi tire on my bike now.

--Blair
"Well...0 psi, but I'm going to
fix that before my morning ride..."

Quoted message said:

Dear Greg,

Here's the answer, to quote from elsewhere in this thread:

The 110 psi nonsense is from another poster.

Since no one appears to be willing to perform the simple experiment,

You presume it needs to be performed.

Quoted message said:

here's a picture of what happens if you try to pump an unconstrained
700c inner tube up:

http://home.comcast.net/~carlfogel/download/212_700c_80_pump_strokes_0_psi_4_feet_wide.jpg
or http://tinyurl.com/n3bxa

After 80 strokes with a large floor pump, the 700c tube has obviously
expanded far beyond the 700c rim. The tape measure indicates a 4-foot
wide circle.

The pump indicator registered 0 psi, but the picture showing that
proves only that the shiny glass over the indicator reflects my
camera's automatic flash amazingly well.

Something as broad and heavy as my size 12 shoe with half my 190 pound
weight on it will easily flatten the inflated tube.

Another way to show how little load can be carried is to simply twist
the tube--it's almost effortless to twist it and constrict the section
between your hands into a tiny knot because there's so little tension
in the sidewall.

Mercifully, the tube did not explode. Instead, it sprang a hissing
leak at a seam, typical behavior for such over-expanded tubes.

None of which is relevant to how a tire works.

An innertube at 1.5 bar is not a bicycle tire.

Nor does a bicycle tire necessarily have to be inelastic.

It's just easier that way, given common materials.

--Blair