Exploding tires II

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:

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

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.

Quoted message said:

Quoted message said:

Quoted message said:

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

Quoted message said:

Frank Krygowski 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, 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]

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).

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

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

Quoted message said:

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:

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

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 said:

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

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.

You want a real hazard? Try riding an medium-gear fixed wheel bicycle
down a long 16% hill with just a front brake. You're on the verge of
spinning out at 150rpm (or 200rpm if you're a track ace), the brake
smells like burning Bakelite, and then you remember you pumped up the
front tyre until it was rock hard. Do you:

[ ] release the brake and let the bike throw you off
[ ] pray the front tyre doesn't explode
[ ] aim for the hedge?

I was there a couple of weeks ago. I chose option 2 and the tyre held,
but on a real mountain I'd have been toast.

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).

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.

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.

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.

So, two possible solutions:

1) Hollow spokes delivering cooling water on demand to the inner
surface of the rim. Reservoir under the saddle, connected to a suitable
fitting at the hub. The optimum rim design would be like the old
Weinmann Concave rims mentioned in another thread, so the water would be
kept at the inner surface and away from the braking surfaces. (A Mr.
Goldberg may already have a patent on this ides, of course.)

2) The water-filled inner tubes from yet another thread.

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

Frank Krygowski said:

So, two possible solutions:

1) Hollow spokes delivering cooling water on demand to the inner
surface of the rim. Reservoir under the saddle, connected to a suitable
fitting at the hub. The optimum rim design would be like the old
Weinmann Concave rims mentioned in another thread, so the water would be
kept at the inner surface and away from the braking surfaces. (A Mr.
Goldberg may already have a patent on this ides, of course.)

2) The water-filled inner tubes from yet another thread.

3) Disc brakes.

Austin

Jim Smith said:

"Mike Jacoubowsky" <[email hidden]> writes:

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.

For those less adept at the computation:

For a cyclist continually braking while descending a constant slope (s),
the speed that generates the maximum power dissipation in the brakes is

Vwc = Vt/sqrt(3).

The max power dissipated in the brakes is

Pmax = 2/(3*sqrt(3)) * Fg*Vt

where
Vt = terminal velocity of rider (descending w/out braking)
Fg = s*m*g
s = slope of road
m = mass of bike and rider
g = gravitational acceleration.

Plugging in some typical values

m = 225lb = 68kg
s = 10% = 0.10
Vt = 54mph = 87kph [a guess]
Fg = 10m/s^2

we get

Vwc = 50kph = 31*mph
Pmax = 930watt,

which is about what Jim came up.

Joe Riel

[email hidden] wrote in message ...

Quoted message said:

Frank Krygowski 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:

> 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.

It may predominantly be the braking in itself which causes the tyre to be
pulled around the rim and so release the tyres grip on the rim, it is only
typical tube pressure which then lifts the tyre from the rim. Degreasing of
the rim and tyre before fitting will ensure satisfactory adhesion to prevent
this lifting. Alternatively use tubulars.

Trevor

[email hidden] wrote in message ...

Quoted message said:

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.

Should have been using tub's. Not liable to snakebites. No snake can catch
yer. Tubs will flat over 30min's due to the close fit between tyre and
tube, not generally available with wired on tyres.

Trevor

Frank Krygowski wrote in message <[email hidden]>...

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!"

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.

Blow off proof tyre - tubular.

Trevor

Peter said:

Quoted message said:

Tom Sherman 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

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.

Your presumption is correct.

The name of the author of the site [1], Morscher is suspicious in light
of its English translation, "more rotten".

[1] The "tinyurl" link seems broken:
<http://www.sagen.at/texte/gegenwart/oesterreich/tirol/allgemein/picknickamzirlerberg.htm>.

--
Tom Sherman

AustinMN said:

Frank Krygowski said:

So, two possible solutions:

1) Hollow spokes delivering cooling water on demand to the inner
surface of the rim. Reservoir under the saddle, connected to a
suitable fitting at the hub. The optimum rim design would be like the
old Weinmann Concave rims mentioned in another thread, so the water
would be kept at the inner surface and away from the braking
surfaces. (A Mr. Goldberg may already have a patent on this idea, of
course.)

2) The water-filled inner tubes from yet another thread.

3) Disc brakes.

<sigh> There's always someone who wants to take the easy way out.

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