Exploding tires II

Brian said:

air at -15 degrees, pumped in at 90 ppsi, then allowed to warm to +20
degrees or warmer? Gee, THAT shouldn't cause a problem, should it???

Actually, I'm very surprised it did. The resulting pressure should have
been about 103 psi. That's usually not high enough to cause a problem.

It's the ratio of the _absolute_ temperatures that matters, not the
ratio of the Celsius temperatures.

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

Quoted message said:

Quoted message said:

air at -15 degrees, pumped in at 90 ppsi, then allowed to warm to +20
degrees or warmer? Gee, THAT shouldn't cause a problem, should it???

Actually, I'm very surprised it did. The resulting pressure should have
been about 103 psi. That's usually not high enough to cause a problem.

It's the ratio of the _absolute_ temperatures that matters, not the ratio
of the Celsius temperatures.

For those of us who have forgotten our high-school physics, could you give a
few examples of absolute vs Celsius (or Fahrenheit) temperatures? In the
real world, we might conceivably see a tire/tube start the day at 40 degrees
(F) and reach a peak of well over 100 (F), possibly 150? To tell you the
truth, I don't honestly know just how hot the air in a tube might get on a
very long, very steep descent with ambient air temp at 90 degrees. However,
that's a real-world example that some of us experience.

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

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

Quoted message said:

Quoted message said:

Quoted message said:

air at -15 degrees, pumped in at 90 ppsi, then allowed to warm to +20
degrees or warmer? Gee, THAT shouldn't cause a problem, should it???

Actually, I'm very surprised it did. The resulting pressure should have
been about 103 psi. That's usually not high enough to cause a problem.

It's the ratio of the _absolute_ temperatures that matters, not the

ratio

Quoted message said:

Quoted message said:

of the Celsius temperatures.

For those of us who have forgotten our high-school physics, could you give

a

Quoted message said:

few examples of absolute vs Celsius (or Fahrenheit) temperatures? In the
real world, we might conceivably see a tire/tube start the day at 40

degrees

Quoted message said:

(F) and reach a peak of well over 100 (F), possibly 150? To tell you the
truth, I don't honestly know just how hot the air in a tube might get on a
very long, very steep descent with ambient air temp at 90 degrees.

However,

Quoted message said:

that's a real-world example that some of us experience.

Roughly speaking and assuming the tire volume doesn't change and air is
neither added to nor removed from the tire then the pressure is proportional
to the temperature expressed in degrees Kelvin. 0 degrees Celsius is 273
deg.K. Therefore we're talking about a tire going from 258 deg. K to 293
deg. K. If the pressure at 258K is 90 psi then the pressure at 293K will be
approximately 293/258 X 90 = 102 psi.

Quoted message said:

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

Kelvin = 273.15 + Celcius
(Farenheit -32) * 5/9 gives celcius
Pressure increases proportionally with Kelvin tempature (unless near
condensation point of the gases involved).

Desert, 32F 0C 273K dawn pump to 100 PSI
104F 40C 313K afternoon shade to 114 PSI
212F 100C 373K afternoon in sun with black tires getting soft to 136 PSI

a couple of years ago, at the Springfield IL iron man triathalon,
everyone pumps up their tires in the early morning dawn when it is
cool. After swimming 1/2 miles and running 5 miles, they got back,
after heating in the sun, hopped on their bikes and several tires blew
in from the increased pressure. Once person rode on his flat 45 miles
instead of putting on another tire.

Mike Jacoubowsky said:

Quoted message said:

Quoted message said:

air at -15 degrees, pumped in at 90 ppsi, then allowed to warm to +20
degrees or warmer? Gee, THAT shouldn't cause a problem, should it???

Actually, I'm very surprised it did. The resulting pressure should have
been about 103 psi. That's usually not high enough to cause a problem.

It's the ratio of the _absolute_ temperatures that matters, not the ratio
of the Celsius temperatures.

For those of us who have forgotten our high-school physics, could you give a
few examples of absolute vs Celsius (or Fahrenheit) temperatures? In the
real world, we might conceivably see a tire/tube start the day at 40 degrees
(F) and reach a peak of well over 100 (F), possibly 150? To tell you the
truth, I don't honestly know just how hot the air in a tube might get on a
very long, very steep descent with ambient air temp at 90 degrees. However,
that's a real-world example that some of us experience.

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

"Ian S" wrote: (clip) If the pressure at 258K is 90 psi then the pressure
at 293K will be approximately 293/258 X 90 = 102 psi.
^^^^^^^^^^^^^
I have one more little nit to pick, but since we're talking physics here,
you need to remember that 90 PSIG = 105 PSIA*. So 293/258 x 104 = 118 PSIA,
which is 103 PSIG.

* PSIG = Gauge pressure. PSIA = Absolute pressure = Gauge pressure + 15.

Not very important to a bicyclist, but TERRIBLY important to someone grading
a high school physics exam. :-)

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

Quoted message said:

"Ian S" wrote: (clip) If the pressure at 258K is 90 psi then the

pressure

Quoted message said:

at 293K will be approximately 293/258 X 90 = 102 psi.
^^^^^^^^^^^^^
I have one more little nit to pick, but since we're talking physics here,
you need to remember that 90 PSIG = 105 PSIA*. So 293/258 x 104 = 118

PSIA,

Quoted message said:

which is 103 PSIG.

* PSIG = Gauge pressure. PSIA = Absolute pressure = Gauge pressure + 15.

Not very important to a bicyclist, but TERRIBLY important to someone

grading

Quoted message said:

a high school physics exam. :-)

So where'd the 104 in your calculation come from?

"Ian S" wrote: So where'd the 104 in your calculation come from?
^^^^^^^^^^^^^
Sorry--my error. The first time I wrote it, I treated atmospheric pressure
as 24 psi. Then, when I edited it, I overlooked that entry. Take off five
points.

Mike Jacoubowsky said:

For those of us who have forgotten our high-school physics, could

you give a

Quoted message said:

few examples of absolute vs Celsius (or Fahrenheit) temperatures? In the
real world, we might conceivably see a tire/tube start the day at 40 degrees
(F) and reach a peak of well over 100 (F), possibly 150? To tell you the
truth, I don't honestly know just how hot the air in a tube might get on a
very long, very steep descent with ambient air temp at 90 degrees. However,
that's a real-world example that some of us experience.

OK, the relationship is (P1*V1)/T1 = (P2*V2)/T2 where P and T refer to
absolute pressures and temperatures, V is volume. If volume is
(reasonably) assumed constant, it cancels out, and you can rearrange to:

P2 = P1 *(T2/T1)

But again, P & T have to be measured on absolute scales. They're
usually not, so you have to convert.

For metric measurements like the originally quoted Celsius, the absolute
temperature scale is Kelvin. To convert Celsius to Kelvin, add 273.15

If you're starting with degrees Fahrenheit, the corresponding absolute
scale is Rankine. To convert Fahrenheit to Rankine, add 459.67 (or
alternately, convert Fahrenheit to Celsius and use the Kelvin scale.)

For pressures, your gage measures "gage pressure," psig. To convert to
absolute pressure (psia) add the pressure of the atmosphere, 14.7 psia.

So, 40 deg. F = 499.67 deg R 150 deg F = 609.67 deg R
90 psig = 104.7 psia

and P2 = 104.7 psia*(609.67/499.67) = 127.7 psia

But now we have to get that absolute pressure converted back to gage
pressure. Subtract 14.7 and you get P2 = 113 psig.

So in general, it's not as bad as you might think.

There are commercially available stick-on temperature indicators that
record maximum temperatures of the surface to which they're stuck.
http://www.tempil.com/Tempilabel.htm

ISTR someone checking tandem rims on mountain descents with these
things, but I don't recall what the maximum temperature was.

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

Ian S said:

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

Quoted message said:

Quoted message said:

>air at -15 degrees, pumped in at 90 ppsi, then allowed to warm to +20
>degrees or warmer? Gee, THAT shouldn't cause a problem, should it???

Actually, I'm very surprised it did. The resulting pressure should have
been about 103 psi. That's usually not high enough to cause a problem.

It's the ratio of the _absolute_ temperatures that matters, not the

ratio

Quoted message said:

Quoted message said:

of the Celsius temperatures.

For those of us who have forgotten our high-school physics, could you give

a

Quoted message said:

few examples of absolute vs Celsius (or Fahrenheit) temperatures? In the
real world, we might conceivably see a tire/tube start the day at 40

degrees

Quoted message said:

(F) and reach a peak of well over 100 (F), possibly 150? To tell you the
truth, I don't honestly know just how hot the air in a tube might get on a
very long, very steep descent with ambient air temp at 90 degrees.

However,

Quoted message said:

that's a real-world example that some of us experience.

Roughly speaking and assuming the tire volume doesn't change and air is
neither added to nor removed from the tire then the pressure is proportional
to the temperature expressed in degrees Kelvin. 0 degrees Celsius is 273
deg.K. Therefore we're talking about a tire going from 258 deg. K to 293
deg. K. If the pressure at 258K is 90 psi then the pressure at 293K will be
approximately 293/258 X 90 = 102 psi.

Might be easier to invoke the Rankine scale, which also gives absolute
temperatures but is easier to relate to the common Farenheit scale
(degrees R = degrees F + 459). Mike's example would then start at 40F =
499R and heat up to 150F = 609R. Assuming a 90 psi tire in the morning,
the long hot downhill ride would hit (609/499 x 90 psi) = 110 psi.
(Note Ian was calculating the pressure change for Brian's Canadian
store, not Mike's example. The answers should be different!)

I don't question Brian's claim that the department store tires popped
when they came inside. But given the pressure change in Mike's example,
I wouldn't want to ride one of those bikes down a long hill on a summer
afternoon!

Pat

Frank Krygowski said:

Mike Jacoubowsky said:

For those of us who have forgotten our high-school physics, could

you give a

Quoted message said:

few examples of absolute vs Celsius (or Fahrenheit) temperatures? In
the real world, we might conceivably see a tire/tube start the day at
40 degrees (F) and reach a peak of well over 100 (F), possibly 150? To
tell you the truth, I don't honestly know just how hot the air in a
tube might get on a very long, very steep descent with ambient air temp
at 90 degrees. However, that's a real-world example that some of us
experience.

OK, the relationship is (P1*V1)/T1 = (P2*V2)/T2 where P and T refer to
absolute pressures and temperatures, V is volume. If volume is
(reasonably) assumed constant, it cancels out, and you can rearrange to:

P2 = P1 *(T2/T1)

But again, P & T have to be measured on absolute scales. They're
usually not, so you have to convert.

For metric measurements like the originally quoted Celsius, the absolute
temperature scale is Kelvin. To convert Celsius to Kelvin, add 273.15

If you're starting with degrees Fahrenheit, the corresponding absolute
scale is Rankine. To convert Fahrenheit to Rankine, add 459.67 (or
alternately, convert Fahrenheit to Celsius and use the Kelvin scale.)

For pressures, your gage measures "gage pressure," psig. To convert to
absolute pressure (psia) add the pressure of the atmosphere, 14.7 psia.

So, 40 deg. F = 499.67 deg R 150 deg F = 609.67 deg R
90 psig = 104.7 psia

and P2 = 104.7 psia*(609.67/499.67) = 127.7 psia

But now we have to get that absolute pressure converted back to gage
pressure. Subtract 14.7 and you get P2 = 113 psig.

So in general, it's not as bad as you might think.

There are commercially available stick-on temperature indicators that
record maximum temperatures of the surface to which they're stuck.
http://www.tempil.com/Tempilabel.htm

ISTR someone checking tandem rims on mountain descents with these
things, but I don't recall what the maximum temperature was.

Long response, wow.
I think the main thing is that the tire/tube combination is much
more sensitive to temperature than the change in air pressure.
Rubber like materials don't fare well over about 150 F.
Hot pavement with braking on a long descent can cause material
troubles.
Bill Baka

--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Frank Krygowski said:

For metric measurements like the originally quoted Celsius, the
absolute temperature scale is Kelvin. To convert Celsius to Kelvin,
add 273.15

Quoted message said:

If you're starting with degrees Fahrenheit, the corresponding
absolute scale is Rankine. To convert Fahrenheit to Rankine, add
459.67 (or alternately, convert Fahrenheit to Celsius and use the
Kelvin scale.)

Quoted message said:

For pressures, your gage measures "gage pressure," psig. To convert
to absolute pressure (psia) add the pressure of the atmosphere, 14.7
psia.

Quoted message said:

So, 40 deg. F = 499.67 deg R 150 deg F = 609.67 deg R
90 psig = 104.7 psia

Quoted message said:

and P2 = 104.7 psia*(609.67/499.67) = 127.7 psia

Quoted message said:

But now we have to get that absolute pressure converted back to gage
pressure. Subtract 14.7 and you get P2 = 113 psig.

Quoted message said:

So in general, it's not as bad as you might think.

Actually things are worse than you think because rims get much hotter
than suspected. My first introduction to how high rims get was with
steam generated from water in the rim on a mild descent with hairpin
turns at the end of several straight runs. The experience also showed
that on exiting the turn, steam stopped escaping which revealed how
fast air cooling reduces rim temperatures.

That rim heating is significant has been experienced by tandem riders
who ride in mountains as well as singles on steep roads such as those
in Austria, typically Zirlerberg with winding 18% grade and where
bicycling are absolutely prohibited downhill, and for good reason.
Even for cares and trucks, several steep run-away tracks exit from
curves in the event of brake failure.

http://tinyurl.com/jhiu

Quoted message said:

There are commercially available stick-on temperature indicators that
record maximum temperatures of the surface to which they're stuck.
http://www.tempil.com/Tempilabel.htm

Forget about that, it's both temperature and duration that cause
dangerous heating and overpressure blow-offs. I've done it as have
others with whom I have ridden on steep roads. Unobservant riders
might attribute the blow-off to a faulty tire or poor tire mounting but
it is heat.

Quoted message said:

ISTR someone checking tandem rims on mountain descents with these
things, but I don't recall what the maximum temperature was.

After you have ridden a few hundred miles in mountainous terrain and
then have a blow-off should be definitive.

Jobst Brandt
[email hidden]

Quoted message said:

Frank Krygowski said:

There are commercially available stick-on temperature indicators that
record maximum temperatures of the surface to which they're stuck.
http://www.tempil.com/Tempilabel.htm

Forget about that, it's both temperature and duration that cause
dangerous heating and overpressure blow-offs. I've done it as have
others with whom I have ridden on steep roads. Unobservant riders
might attribute the blow-off to a faulty tire or poor tire mounting but
it is heat.

As a guy who likes data, I'd still be interested in a "maximum
temperature" reading. If someone wanted to log temperature versus time
instead, that would be even more interesting, but much more difficult.

Quoted message said:

Quoted message said:

ISTR someone checking tandem rims on mountain descents with these
things, but I don't recall what the maximum temperature was.

After you have ridden a few hundred miles in mountainous terrain and
then have a blow-off should be definitive.

I've done the first, but not the second. I'd hope to find a less scary
way of learning about this!

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

Quoted message said:

Actually things are worse than you think because rims get much hotter
than suspected. My first introduction to how high rims get was with
steam generated from water in the rim on a mild descent with hairpin
turns at the end of several straight runs. The experience also showed
that on exiting the turn, steam stopped escaping which revealed how
fast air cooling reduces rim temperatures.

So perhaps for a cheap thrill or two, a cyclist could put a small amount of
colored water (to make the steam easier to observe) into their rim prior to
a descent?

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).

I have seen a far greater number of tubes exhibiting snake-bite-type damage
(as you'd see on a compression cut) on "blowouts" on steep descents, making
me wonder if the material properties of the rubber itself change (for the
worse) as temperatures rise.

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
IMBA, BikesBelong, NBDA member

Frank Krygowski said:

Quoted message said:

Quoted message said:

There are commercially available stick-on temperature indicators that
record maximum temperatures of the surface to which they're stuck.
http://www.tempil.com/Tempilabel.htm

Quoted message said:

Quoted message said:

Forget about that, it's both temperature and duration that cause
dangerous heating and overpressure blow-offs. I've done it as have
others with whom I have ridden on steep roads. Unobservant riders
might attribute the blow-off to a faulty tire or poor tire mounting
but it is heat.

Quoted message said:

As a guy who likes data, I'd still be interested in a "maximum
temperature" reading. If someone wanted to log temperature versus
time instead, that would be even more interesting, but much more
difficult.

Quoted message said:

Quoted message said:

Quoted message said:

ISTR someone checking tandem rims on mountain descents with these
things, but I don't recall what the maximum temperature was.

Quoted message said:

Quoted message said:

After you have ridden a few hundred miles in mountainous terrain
and then have a blow-off should be definitive.

Quoted message said:

I've done the first, but not the second. I'd hope to find a less
scary way of learning about this!

OK, nothing lost if you put a few heat indicators on your rear rim,
find a steep road (steeper than 12%) in your area and with a tire
inflated over 100psi, roll down the hill at between 5 and 8 mph with
only the rear brake applied. When the tire blows off, use the front
brake to stop and check the highest temperature reached. This will
cost you no more than one tube, preferably one that had a few patches.
There is no hazard here if you don't have any tight turns.

This is an easy test that I have done inadvertently without
instrumentation. I'm satisfied that it occurs easily. I have had an
opportunity to testify on a tandem case where the rider concocted a
story that was immediately apparent to me, because the scenario was
based on the belief that brake heating did not cause the tire to bow
off. I could prove by the evidence on the bicycle that his story was
false and also how the failure actually occurred.

Jobst Brandt
[email hidden]

Mike Jacoubowsky said:

Quoted message said:

Actually things are worse than you think because rims get much
hotter than suspected. My first introduction to how high rims get
was with steam generated from water in the rim on a mild descent
with hairpin turns at the end of several straight runs. The
experience also showed that on exiting the turn, steam stopped
escaping which revealed how fast air cooling reduces rim
temperatures.

Quoted message said:

So perhaps for a cheap thrill or two, a cyclist could put a small
amount of colored water (to make the steam easier to observe) into
their rim prior to a descent?

What would colored water do?

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).

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:

I have seen a far greater number of tubes exhibiting snake-bite-type
damage (as you'd see on a compression cut) on "blowouts" on steep
descents, making me wonder if the material properties of the rubber
itself change (for the worse) as temperatures rise.

It makes no difference, the tire blows off the rim. That is why you
hear a loud bang that produces a long slash in the tube.

http://draco.acs.uci.edu/rbfaq/FAQ/8b.4.html

Jobst Brandt
[email hidden]

Quoted message said:

OK, nothing lost if you put a few heat indicators on your rear rim,
find a steep road (steeper than 12%) in your area and with a tire
inflated over 100psi, roll down the hill at between 5 and 8 mph with
only the rear brake applied. When the tire blows off, use the front
brake to stop and check the highest temperature reached. This will
cost you no more than one tube, preferably one that had a few patches.
There is no hazard here if you don't have any tight turns.

No hazard of crashing maybe, but when it happened to me I had a big welt
on the side of my calf from the explosion. I suggest wearing protective
clothing if anyone tries this.

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

Quoted message said:

Mike Jacoubowsky writes:

[...]

Quoted message said:

Quoted message said:

So perhaps for a cheap thrill or two, a cyclist could put a small
amount of colored water (to make the steam easier to observe) into
their rim prior to a descent?

What would colored water do?

Make coloured steam.

--

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

Mike Jacoubowsky/Chain Reaction Bicycles 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).

I have seen a far greater number of tubes exhibiting snake-bite-type damage
(as you'd see on a compression cut) on "blowouts" on steep descents, making
me wonder if the material properties of the rubber itself change (for the
worse) as temperatures rise.

Checking the Matweb site,
http://www.matweb.com/search/SpecificMaterial.asp?bassnum=P0RUB1
for properties of vulcanized natural rubber, there are two things that
strike me as interesting.

One is "Maximum service temperature, Air = 176 deg. F." They don't
specify the consequences of exceeding this, and I don't know if they're
related to long term degredation or short term failure, but it's
interesting.

The other is the coefficient of thermal expansion, 125 microinches per
inch per degree F. That's pretty high, of course, about ten times as
much as aluminum and 20 times steel.

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 distorion of the bead shape, and cause the
bead to lose its grip on the rim?

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

DRS said:

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

Quoted message said:

Mike Jacoubowsky writes:

[...]

Quoted message said:

Quoted message said:

So perhaps for a cheap thrill or two, a cyclist could put a small
amount of colored water (to make the steam easier to observe) into
their rim prior to a descent?

What would colored water do?

Make coloured steam.

Too bad it isnt that easy.