Exploding tires II

Frank Krygowski said:

Quoted message said:

Quoted message said:

I wonder about the change in the interface between the tire and
the rim when the dimensions change with temperature. The steel
bead wire (assuming that's what you've got) would change the
least, by virtue of lowest coefficient and being most insulated.
The rim would grow a bit (tightening the fit, I suppose), but the
rubber would be trying to grow significantly. Is there a chance
this (combined with, say, softening at higher temps) would cause
distortion of the bead shape, and cause the bead to lose its grip
on the rim?

Quoted message said:

Quoted message said:

It's the clinch, not the wire. Wire bead tires blow off the rim
equally well with Kevlar ones. Believe me, I've tried it and observed
it. Stop raising new specters behind every turn. Brake heating
causes blow-offs. Accept it!

Quoted message said:

Quoted message said:

What is this all about anyway. What are you trying to generate?

Quoted message said:

Jobst, it's a discussion. I'm just curious about the details of the
phenomenon! Saying "Accept it!" about tires blowing off the rim
this is like saying "Accept it, people die of cholera!"

You use an odd way to ask. Telling us what else could cause a tire to
come off the rim, raises specters that attain a life of their own. We
have enough myth and lore to quash without you introducing new ones.
You've been around this newsgroup long enough to have read all this
about tire blow-off several times. That's why I ask "what are you
trying to generate?"

Quoted message said:

If the discussion sheds light to enable someone to design a
blow-off-proof tire, that would be wonderful. If the discussion
merely teaches us something about the physics of the situation, that
would at least be beneficial.

If your idea of discussion is the classic: "Tires blow off because..."
followed by a series of remotely plausible reasons, followed by a
belated,"that's right isn't it?" somewhere in a disconnected
sentence, you are not asking. That is a typical "end run" offered by
folks who have pet ideas but have no way to prove them or substantiate
that they ever occur.

Quoted message said:

As I see it, this is at least as valuable as harping about whether
the word "stretch" should be used to describe elongation of chain
pitch.

Only if you say stretch without defining what you mean by the word.
From misuse of stretch, we have seen many posts in which riders
believe they stretched their chain from riding on too steep a hill.

Quoted message said:

Sheesh!

Quoted message said:

Yes? That is probably appropriate for your stretch of the term

"discussion".

Jobst Brandt
[email hidden]

Mike Jacoubowsky said:

Quoted message said:

Quoted message said:

Are you suspecting that the air temp in the tube actually exceeds
100C? In the 0-100C example, the pressure differential didn't
appear to be enough to blow a (properly mounted) tire off of a rim
(from 100psi to 136psi).

Quoted message said:

Quoted message said:

That depends on how long the tube is exposed to how high a
temperature. What is proven is that you can blow a tire off the
rim with brake heating.

Quoted message said:

That it happens isn't questionable. Why it happens is. A tire
ought to be able to handle a pretty significant amount of pressure
over what it's rated for. A typical tire will easily handle 150psi
before blowing off a rim (easily proven in the shop). But I'm not
seeing the physics (yet) that show a high-enough temperature
differential to accomplish this. That's why I'm thinking there's
more to it than just an increase in pressure.

Did you try riding that wheel with the tire at 150psi? I suspect that
riding it on flatland, with no braking, that it would come off. I am
not convinced by a static test. Would you test ride that?

Jobst Brandt
[email hidden]

Jim Smith said:

Well, a quick back of the email calculation shows that for a bike and
rider weighing 1000N (225lbs) and a 10% grade, maximum energy
dissipation by the brakes will occur at a speed of around 50 km/h. At
that speed the bike is losing gravitational potential energy at a rate
of 1388 watts and it is taking 465 watts for wind and rolling
resistance, so that leaves 923 watts for the brakes to get rid of. If
we are using only one brake that is 923 watts into a 450 gm piece of
Al with a surface area of a few hundred cm^2. I suspect it could get
pretty hot.

Hold the phone! I'll propose that the rim will get hotter at 1/10
that speed because there is practically no convection cooling when
riding slowly. Convection is the primary coolant of rims in the
absence of rain water. Besides, the rate of conversion of kinetic
energy to heat increases with speed until the brake pad fails. Where
do you get 50km/h?

Jobst Brandt
[email hidden]

Quoted message said:

Jim Smith said:

Well, a quick back of the email calculation shows that for a bike and
rider weighing 1000N (225lbs) and a 10% grade, maximum energy
dissipation by the brakes will occur at a speed of around 50 km/h. At
that speed the bike is losing gravitational potential energy at a rate
of 1388 watts and it is taking 465 watts for wind and rolling
resistance, so that leaves 923 watts for the brakes to get rid of. If
we are using only one brake that is 923 watts into a 450 gm piece of
Al with a surface area of a few hundred cm^2. I suspect it could get
pretty hot.

Hold the phone! I'll propose that the rim will get hotter at 1/10
that speed because there is practically no convection cooling when
riding slowly. Convection is the primary coolant of rims in the
absence of rain water. Besides, the rate of conversion of kinetic
energy to heat increases with speed until the brake pad fails. Where
do you get 50km/h?

I should let Jim respond, but from my post it is clear that this
is the speed that maximizes the power dissipation in the brakes.
As you suggest, this may not be the worst-case for rim temperature.

What's a reasonable model for convection losses vs speed?

Joe Riel

Carl Fogel said:

Quoted message said:

Quoted message said:

> On the other hand, I wasn't aware that there was any doubt that rim
> heating cause blow-offs, especially among bicycle shop operators.

Quoted message said:

Quoted message said:

Quoted message said:

There is no question that rim heating causes tube/tire failure.
There is a question as to the mechanism that causes this.
Previously, before the physics was made clear, I had assumed it was
simply high pressure... but since that same amount of pressure
(according to the physics lessons presented in this thread, which
nobody has seriously questioned yet) doesn't accomplish this in the
shop, that causes me to question the assumption.

Quoted message said:

Quoted message said:

The "physics lesson" used an inappropriately low temperature as I
see it.

Quoted message said:

So what's an appropriate rim temperature for your physics
lesson?

Quoted message said:

Elsewhere in this thread, people are calculating rim
temperatures of 570 degrees K (or F, take your pick).

How about starting a 110psi and, following Mike's test of at what
pressur a tire comes off wehn ridden at room temperature, re-evaluate
what temperature that takes. As I said, I could make plenty of steam
on a not-so-steep Alpine pass. I know that you can burn hands
(blisters) at the tempreature I developed on an 18% grade in 500m
using both brakes at 40km/h. I had no way of measuring it but it was
hot enough that we stopped at the runaway lane for the rims to cool to
warm-to-the-touch. There was a breeze on the W?rzen Pass.

Jobst Brandt
[email hidden]

Joe Riel said:

Quoted message said:

Quoted message said:

Well, a quick back of the email calculation shows that for a bike and
rider weighing 1000N (225lbs) and a 10% grade, maximum energy
dissipation by the brakes will occur at a speed of around 50 km/h. At
that speed the bike is losing gravitational potential energy at a rate
of 1388 watts and it is taking 465 watts for wind and rolling
resistance, so that leaves 923 watts for the brakes to get rid of. If
we are using only one brake that is 923 watts into a 450 gm piece of
Al with a surface area of a few hundred cm^2. I suspect it could get
pretty hot.

Hold the phone! I'll propose that the rim will get hotter at 1/10
that speed because there is practically no convection cooling when
riding slowly. Convection is the primary coolant of rims in the
absence of rain water. Besides, the rate of conversion of kinetic
energy to heat increases with speed until the brake pad fails. Where
do you get 50km/h?

Quoted message said:

I should let Jim respond, but from my post it is clear that this
is the speed that maximizes the power dissipation in the brakes.

You are assuming constant speed braking rather than braking for
hairpin turns at the end of free rolling straights. My experience is
that the tube is well insulated by the tire and that heat comes in
mostly by contact with the rim (strip).

Quoted message said:

As you suggest, this may not be the worst-case for rim temperature.

Quoted message said:

What's a reasonable model for convection losses vs speed?

I have no idea. I'm sure there is data on wind speed air temperature
and heat transfer, but that requires a known rim temperature and
speed. As I said, steep slow descents are the bane of tires. These
are where I've seen the blowouts.

Jobst Brandt
[email hidden]

Quoted message said:

Did you try riding that wheel with the tire at 150psi? I suspect that
riding it on flatland, with no braking, that it would come off. I am
not convinced by a static test. Would you test ride that?

Not yet. What are the forces that would, without any braking action, cause
it to come off the rim while being ridden (but not otherwise)? We've
already been through threads explaining that there are virtually no "g
forces" exerted on tires (and thank goodness, since I wouldn't want to be
testing one for blowing off a rim while doing a slalom!).

But maybe I'm looking at the wrong thing. I keep thinking about what would
change in a tire or tube at higher temps that would cause one to blow off a
rim, but maybe it's not the tire that has trouble at (what I consider)
mildly-elevated pressures, but the rim? As pressure on the sides of the rim
increases (due to increasing tire pressure), the sides will bulge out
slightly. Perhaps enough to loosen their grip on the tire bead? And if
higher temperatures turn out to make the sidewall material more slippery?

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

Quoted message said:

Jim Smith said:

Well, a quick back of the email calculation shows that for a bike and
rider weighing 1000N (225lbs) and a 10% grade, maximum energy
dissipation by the brakes will occur at a speed of around 50 km/h. At
that speed the bike is losing gravitational potential energy at a rate
of 1388 watts and it is taking 465 watts for wind and rolling
resistance, so that leaves 923 watts for the brakes to get rid of. If
we are using only one brake that is 923 watts into a 450 gm piece of
Al with a surface area of a few hundred cm^2. I suspect it could get
pretty hot.

Hold the phone! I'll propose that the rim will get hotter at 1/10
that speed because there is practically no convection cooling when
riding slowly. Convection is the primary coolant of rims in the
absence of rain water. Besides, the rate of conversion of kinetic
energy to heat increases with speed until the brake pad fails. Where
do you get 50km/h?

I was just looking at the power input to the rim, which I think we
agree reaches a maximum for this set of numbers somewhere around 50
kmh. At 5 kmh the power to the brakes is about 135 watts.

I am curious how you know that convection is the primary method of
heat transfer from the rims? Has someone measured this? If so, it
seems they would know exactly how hot rims get.

[email hidden] wrote in message ...

Quoted message said:

If your idea of discussion is the classic: "Tires blow off because..."

You should have used tubulars.

Trevor

[email hidden] wrote in message ...

Quoted message said:

Mike Jacoubowsky said:

That it happens isn't questionable. Why it happens is. A tire
ought to be able to handle a pretty significant amount of pressure
over what it's rated for. A typical tire will easily handle 150psi
before blowing off a rim (easily proven in the shop). But I'm not
seeing the physics (yet) that show a high-enough temperature
differential to accomplish this. That's why I'm thinking there's
more to it than just an increase in pressure.

Did you try riding that wheel with the tire at 150psi? I suspect that
riding it on flatland, with no braking, that it would come off. I am
not convinced by a static test. Would you test ride that?

So what pressure does a track cyclist use with 20mm high pressures?
I think it would be near 150psi in most cases.

Trevor

[email hidden] wrote in message ...

Quoted message said:

Jim Smith said:

Well, a quick back of the email calculation shows that for a bike and
rider weighing 1000N (225lbs) and a 10% grade, maximum energy
dissipation by the brakes will occur at a speed of around 50 km/h. At
that speed the bike is losing gravitational potential energy at a rate
of 1388 watts and it is taking 465 watts for wind and rolling
resistance, so that leaves 923 watts for the brakes to get rid of. If
we are using only one brake that is 923 watts into a 450 gm piece of
Al with a surface area of a few hundred cm^2. I suspect it could get
pretty hot.

Hold the phone! I'll propose that the rim will get hotter at 1/10
that speed because there is practically no convection cooling when
riding slowly. Convection is the primary coolant of rims in the
absence of rain water. Besides, the rate of conversion of kinetic
energy to heat increases with speed until the brake pad fails. Where
do you get 50km/h?

You are being ignorant of radiation. And if there is no convection, then
the heat raised is insignificant.

Trevor

Quoted message said:

Quoted message said:

What's a reasonable model for convection losses vs speed?

I have no idea. I'm sure there is data on wind speed air temperature
and heat transfer, but that requires a known rim temperature and
speed.

Which brings us back to: collecting data. To understand this
phenomenon, it makes sense to measure rim temperatures under various
braking conditions.

--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
Substitute cc dot ysu dot
edu]

Quoted message said:

Frank Krygowski said:

Jobst, it's a discussion. I'm just curious about the details of the
phenomenon! Saying "Accept it!" about tires blowing off the rim
this is like saying "Accept it, people die of cholera!"

You use an odd way to ask. Telling us what else could cause a tire to
come off the rim, raises specters that attain a life of their own. We
have enough myth and lore to quash without you introducing new ones.
You've been around this newsgroup long enough to have read all this
about tire blow-off several times. That's why I ask "what are you
trying to generate?"

Quoted message said:

If the discussion sheds light to enable someone to design a
blow-off-proof tire, that would be wonderful. If the discussion
merely teaches us something about the physics of the situation, that
would at least be beneficial.

If your idea of discussion is the classic: "Tires blow off because..."
followed by a series of remotely plausible reasons, followed by a
belated,"that's right isn't it?" somewhere in a disconnected
sentence, you are not asking. That is a typical "end run" offered by
folks who have pet ideas but have no way to prove them or substantiate
that they ever occur.

As I recall, my contribution so far was to demonstrate that the increase
in pressure from a given air temperature is not so great as many people
think. If you want to dispute that, do it mathematically.

Beyond that, I merely pointed to some material properties data and
wondered if they may be relevant. And I suggested actual measurement of
rim temperature to learn more about the problem.

If you prefer we exclude all information and ideas beyond what you
choose to contribute, that puts a burden on you to explain the
phenomenon completely.

Being a man of supreme self-confidence, I'm sure you wouldn't mind
taking on that job - but up to this point, you haven't delivered. And
until you do, you may have to put up with people doing annoying things
like generating hypotheses, posting data, and doing calculations, rather
than just ignorantly "accepting" things, without wondering why.

Quoted message said:

Quoted message said:

As I see it, this is at least as valuable as harping about whether
the word "stretch" should be used to describe elongation of chain
pitch.

Only if you say stretch without defining what you mean by the word.
From misuse of stretch, we have seen many posts in which riders
believe they stretched their chain from riding on too steep a hill.

And the importance of that illusion is greater than the importance of a
blowout on a mountain descent? I think many would disagree.

--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
Substitute cc dot ysu dot
edu]

Jim Smith said:

Quoted message said:

Quoted message said:

Well, a quick back of the email calculation shows that for a bike
and rider weighing 1000N (225lbs) and a 10% grade, maximum energy
dissipation by the brakes will occur at a speed of around 50
km/h. At that speed the bike is losing gravitational potential
energy at a rate of 1388 watts and it is taking 465 watts for wind
and rolling resistance, so that leaves 923 watts for the brakes to
get rid of. If we are using only one brake that is 923 watts into
a 450 gm piece of Al with a surface area of a few hundred cm^2. I
suspect it could get pretty hot.

Quoted message said:

Quoted message said:

Hold the phone! I'll propose that the rim will get hotter at 1/10
that speed because there is practically no convection cooling when
riding slowly. Convection is the primary coolant of rims in the
absence of rain water. Besides, the rate of conversion of kinetic
energy to heat increases with speed until the brake pad fails.
Where do you get 50km/h?

Quoted message said:

I was just looking at the power input to the rim, which I think we
agree reaches a maximum for this set of numbers somewhere around 50
kmh. At 5 kmh the power to the brakes is about 135 watts.

Quoted message said:

I am curious how you know that convection is the primary method of
heat transfer from the rims? Has someone measured this? If so, it
seems they would know exactly how hot rims get.

OK. What other method of cooling comes into play. Radiation is way
down at the temperatures involved. Besides, as I have mentioned,
creeping downhill on a road that otherwise poses no problem, I blew a
tire off the rim as did a colleague on another occasion.

Jobst Brandt
[email hidden]

Carl Fogel said:

Elsewhere in this thread, someone suggested attaching some kind of
temperature-sensitive strips to the rim to show how hot they get. I
suppose that I'll have to pin my hopes on that approach.

I've done that and all the temperature spots turned from silver to
black, indicating that the strips don't go high enough and their
sensitivity to crude.

This was a red tape with silver spots calibrated in degrees. They
turn black when their temperature is reached. I did this long ago and
do not recall the name of the product or how high a temperature they
could read, only that they did not go high enough. Not much was
learned from this experiment.

Jobst Brandt
[email hidden]

Quoted message said:

Carl Fogel said:

Elsewhere in this thread, someone suggested attaching some kind of
temperature-sensitive strips to the rim to show how hot they get. I
suppose that I'll have to pin my hopes on that approach.

I've done that and all the temperature spots turned from silver to
black, indicating that the strips don't go high enough and their
sensitivity to crude.

This was a red tape with silver spots calibrated in degrees. They
turn black when their temperature is reached. I did this long ago and
do not recall the name of the product or how high a temperature they
could read, only that they did not go high enough. Not much was
learned from this experiment.

Maybe it's time for a rerun.

One brand of these is Tempilabel, and at least some of them read up to
500 deg. F. That ought to cover things. See
http://www.tempil.com/pdf/Tempilabel.pdf
or see Omega's offerings at http://www.omega.com/ppt/pptsc.asp?ref=TL-10

As an alternative, an infrared thermometer could be used.
http://www.omega.com/toc_asp/section.asp?book=temperature&section=j

These are non-contact, and might even be rigged to get readings while
riding the bike. These things can measure up to the melting temperature
of aluminum, which is probably enough range.

--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
Substitute cc dot ysu dot
edu]

Mike Jacoubowsky said:

Quoted message said:

Did you try riding that wheel with the tire at 150psi? I suspect that
riding it on flatland, with no braking, that it would come off. I am
not convinced by a static test. Would you test ride that?

Not yet. What are the forces that would, without any braking action, cause
it to come off the rim while being ridden (but not otherwise)? We've
already been through threads explaining that there are virtually no "g
forces" exerted on tires (and thank goodness, since I wouldn't want to be
testing one for blowing off a rim while doing a slalom!).

But maybe I'm looking at the wrong thing. I keep thinking about what would
change in a tire or tube at higher temps that would cause one to blow off a
rim, but maybe it's not the tire that has trouble at (what I consider)
mildly-elevated pressures, but the rim? As pressure on the sides of the rim
increases (due to increasing tire pressure), the sides will bulge out
slightly. Perhaps enough to loosen their grip on the tire bead? And if
higher temperatures turn out to make the sidewall material more slippery?

FWIW, I just remembered a (possibly) related incident.

One summer day a few years ago, I had to drive to work, but I planned to
ride with a friend immediately after work. I had Avocet slicks on the bike.

The car was parked in the sun (don't recall the outside temperature).
When I finished work and drove to the friend's house, I pulled out a
bike with a blown back tire. Obviously, that tire'd blown off the rim
while the car was parked.

Air pressure would have been between 100 psi and 105 psi that morning.
Of course, I don't know the eventual air temperature inside the car. As
a guess, I'd assume the rear tire was partly in the sun as it came
through the rear window. I don't know if it was that part of the tire
that slipped off the rim, though.

What strikes me about this is: there was certainly a rise in
temperature, but I'm sure the rim didn't get anywhere near the boiling
point of water, let alone 500+ degrees. And there was no braking force
which might tend to cause any further shifting, creeping, etc. of the
tire on the rim. All that could have done it would be the (as we've
seen) moderate rise in air pressure, and the possible effects of
temperature on the rubber and other materials.

Unfortunately, it's a one-off "experiment." There is, I suppose, the
chance there was a unique problem with that tire, or its mounting
(although it had plenty of miles on it with no trouble).

If anyone wants to get experimental, they might take a wheel with a
well-mounted tire and pop it in the oven for a few hours!

And for a totally unrelated incident: I once blew a hole right in the
center of the tread of an expensive Clement Campianato Del Mundo Seta
(sp?) tubular, by leaving it parked in the Georgia summer sun. And it
wasn't even noon yet!

--
Frank Krygowski [To reply, remove rodent and vegetable dot com.
Substitute cc dot ysu dot
edu]

"Trevor" <[email hidden]> wrote in message
news:[email hidden]

Quoted message said:

[email hidden] wrote in message ...

Quoted message said:

Mike Jacoubowsky said:

That it happens isn't questionable. Why it happens is. A tire
ought to be able to handle a pretty significant amount of pressure
over what it's rated for. A typical tire will easily handle 150psi
before blowing off a rim (easily proven in the shop). But I'm not
seeing the physics (yet) that show a high-enough temperature
differential to accomplish this. That's why I'm thinking there's
more to it than just an increase in pressure.

Did you try riding that wheel with the tire at 150psi? I suspect
that riding it on flatland, with no braking, that it would come off.
I am not convinced by a static test. Would you test ride that?

So what pressure does a track cyclist use with 20mm high pressures?
I think it would be near 150psi in most cases.

FWIW, when Anna Meares was interviewed the other night at one point she said
she was running at 220psi, but obviously she was using tubulars.

--

A: Top-posters.
Q: What is the most annoying thing on Usenet?

Quoted message said:

Mike Jacoubowsky said:

Quoted message said:

>Are you suspecting that the air temp in the tube actually exceeds
>100C? In the 0-100C example, the pressure differential didn't
>appear to be enough to blow a (properly mounted) tire off of a rim
>(from 100psi to 136psi).

Quoted message said:

Quoted message said:

That depends on how long the tube is exposed to how high a
temperature. What is proven is that you can blow a tire off the
rim with brake heating.

Quoted message said:

That it happens isn't questionable. Why it happens is. A tire
ought to be able to handle a pretty significant amount of pressure
over what it's rated for. A typical tire will easily handle 150psi
before blowing off a rim (easily proven in the shop). But I'm not
seeing the physics (yet) that show a high-enough temperature
differential to accomplish this. That's why I'm thinking there's
more to it than just an increase in pressure.

Did you try riding that wheel with the tire at 150psi? I suspect that
riding it on flatland, with no braking, that it would come off. I am
not convinced by a static test. Would you test ride that?

I have, and the tire didn't come off. I have a set of
Vredestein Fortezza Pista tires, which are spec.'ed with a
maximum pressure of 145 psi. When competing in time trials
of up to 40 km, I have been known to inflate them to maximum
pressure, or maybe a smidgen more. I also compete in roller
races where I inflate these tires to 160 psi. They are
mounted on a set of Campagnolo Shamal wheels. They have
never even given a hit of coming off.

Mark McMaster
[email hidden]

Frank Krygowski said:

Quoted message said:

Quoted message said:

Elsewhere in this thread, someone suggested attaching some kind of
temperature-sensitive strips to the rim to show how hot they
get. I suppose that I'll have to pin my hopes on that approach.

Quoted message said:

Quoted message said:

I've done that and all the temperature spots turned from silver to
black, indicating that the strips don't go high enough and their
sensitivity to crude.

Quoted message said:

Quoted message said:

This was a red tape with silver spots calibrated in degrees. They
turn black when their temperature is reached. I did this long ago
and do not recall the name of the product or how high a temperature
they could read, only that they did not go high enough. Not much
was learned from this experiment.

Quoted message said:

Maybe it's time for a rerun.

Quoted message said:

One brand of these is Tempilabel, and at least some of them read up
to 500 deg. F. That ought to cover things. See:

http://www.tempil.com/pdf/Tempilabel.pdf

Quoted message said:

or see Omega's offerings at:

http://www.omega.com/ppt/pptsc.asp?ref=TL-10

Quoted message said:

As an alternative, an infrared thermometer could be used.

http://www.omega.com/toc_asp/section.asp?book=temperature&section=j

If you've got one, make some measurements,

Quoted message said:

These are non-contact, and might even be rigged to get readings
while riding the bike. These things can measure up to the melting
temperature of aluminum, which is probably enough range.

How else do you measure infrared radiation it not optically.

Jobst Brandt
[email hidden]