Exploding tires II

wrote:

...
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 writes:

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/Specifi...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 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.

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.

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

Tom Sherman writes:

... 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?

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/...5/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

wrote:

Tom Sherman writes:


... 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?


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/...5/Hwy_5N_C.htm

Yes, they're quite common. I presume Tom was referring to the
story on the page you first referenced. It refers to a Polish family
that made the unfortunate choice to have their picnic at the site of the
emergency runaway lane. While they were there a truck with a 40 ton
load lost its brakes and needed to use the lane.

What would colored water do?

Make coloured steam.


Too bad it isnt that easy.

But you get the idea. Add something to the water so the steam is colored.
Then you can pretend you're the Great Waldo Pepper on a bike.

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

wrote:

Frank Krygowski wrote:
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, 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!"

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.

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

Sheesh!

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

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.

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.

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


wrote in message
...
Mike Jacoubowsky writes:

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?

What would colored water do?

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.

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

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/...5/Hwy_5N_C.htm

There are presently at least two runaway truck ramps on I5 northbound (at
least there were Sunday night when I rode past), as well as a number of them
on westbound I80 in the Sierras. Just out of curiosity, I always look for
evidence of recent use when I pass them, but I suspect they "recondition"
them after each incident (smooth out the gravel).

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

Mike Jacoubowsky wrote:
There are presently at least two runaway truck ramps on I5 northbound (at
least there were Sunday night when I rode past), as well as a number of
them on westbound I80 in the Sierras. Just out of curiosity, I always
look for evidence of recent use when I pass them, but I suspect they
"recondition" them after each incident (smooth out the gravel).

While every situation is different, every runaway truck ramp does get used.
For some, it may be a couple times a year, for others it may be a couple
years between uses, but they justify their existence.

Austin