Re: Exploding tires II

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]

On Tue, 24 Aug 2004 18:04:11 GMT,
[email hidden] wrote:

[snip frank]

[snip jobst]

Quoted message said:

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.

[snip jobst]

Quoted message said:

Jobst Brandt
[email hidden]

Dear Jobst,

Is this rapid heat loss after you exit the turn and stop
braking mostly air cooling, radiating, or convection into
the tires, tube, and compressed air?

I think that you've mentioned a tire bursting when you were
just dawdling down a steep hill, barely riding the brake at
around 10 mph while waiting for a friend who'd stopped to
take a picture, so this would seem to support air cooling.

But I'm wondering how much heat just radiates off the huge
exposed surface area of the rim in still air and how much
heat is absorbed by the tire-tube-compressed-air covering
the unexposed surface.

Are the other two heat losses negligible?

Carl Fogel

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]

Carl Fogel said:

Quoted message said:

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:

Is this rapid heat loss after you exit the turn and stop braking
mostly air cooling, radiating, or convection into the tires, tube,
and compressed air?

In this case it probably went into making steam but air cooling is a
major sink judging from the absence of blow-offs when I descent the
same road fast.

Quoted message said:

I think that you've mentioned a tire bursting when you were just
dawdling down a steep hill, barely riding the brake at around 10 mph
while waiting for a friend who'd stopped to take a picture, so this
would seem to support air cooling.

This was on a 12%+ grade on which I was waiting for my friend who was
taking pictures. For convenience I used only the rear brake so I
could easily look over my shoulder. I have ridden this route often
with no problem, before that and since with the same normal inflation
pressure. It is also not the first descent encountered on my European
bicycle tour.

Quoted message said:

But I'm wondering how much heat just radiates off the huge exposed
surface area of the rim in still air and how much heat is absorbed
by the tire-tube-compressed-air covering the unexposed surface.

Enough to blow the tire off.

Quoted message said:

Are the other two heat losses negligible?

I don't know or care.

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.

On Tue, 24 Aug 2004 22:57:21 GMT, "Mike Jacoubowsky/Chain Reaction

Bicycles 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.

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

I wonder if the tube gets the snakebite cut after the blowout, before
the rider comes to a stop?

dianne_1234567890? said:

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.

Quoted message said:

I wonder if the tube gets the snakebite cut after the blowout,
before the rider comes to a stop?

That's a red herring! If the tire got a flat first, then what made it
blow off the rim and go BANG! This makes no sense.

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

Jobst Brandt
[email hidden]

<[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.

Quoted message said:

...
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

Is this actually a bad Polish joke?

--
Tom Sherman

Wow...

Did I open a can 'o worms or what??

My thanks to Frank K, author of the first reply...yes, I did the math and
the pressure due to increased temp (25 C) did indeed raise the psi in the
tyres to @ 100-105 psi

For those who asked, yes -15 C is indeed below freezing - around 0 F.

-and +25 = @ 80 F, give or take a degree or two.

These were dept store roadies of early 80's vintage: steel wheels,cheap
tubes, cheap tyres; and although the tyres were rated for 90 psi, I suspect
they couldn't safely hold much more pressure than that...

....and did I say "explode"? It was actually just yer run-of-the-mill pinch
blowout...

Thanks again for the lively discussion...

Frank Krygowski 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:

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.

Quoted message said:

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.

Quoted message said:

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 degradation or short term failure, but
it's interesting.

This is service temperature, not peak survival temperature, which is
far higher. There is also the problem of tube adhesion to the tire
casing, which is also enhanced by higher temperature. I just got a
snake bite flat that went down over about 30 seconds, mainly because
the tube was securely adhering to the tire. After the tube was out of
the tire it leaked like a sieve.

Quoted message said:

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.

So with 200 F the tube would increase in length by about 5/8 of an
inch if it were free to do so... but it's not so who cares.

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?

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!

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

Jobst Brandt
[email hidden]

Tom Sherman said:

Quoted message said:

... 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:

Is this actually a bad Polish joke?

What do you find odd about this. There are runaway tracks on US
railroads and highways. The Grapevine in California was equipped
with these before it became Interstate-5 and in this web site, take a
look at runaway lanes in America:

http://modena.intergate.ca/personal/pl8s/BC5/Hwy_5N_C.htm

Railroads use them as well. In San Francisco, the Geary-B car had one
before the Cliff house before that line was abandoned. RR switches
can generally not be set for straight through traffic until a train
stops to prove its ability to stop.

Jobst Brandt
[email hidden]

Quoted message said:

Frank Krygowski writes:

[snip]

Quoted message said:

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

Jobst Brandt
[email hidden]

Dear Jobst,

Frank is displaying a trait called curiosity. It worries
some people.

Carl Fogel