From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Rim Strips?
Date: 9 Aug 1996 19:25:42 GMT

John T. Rasper writes:

> What is the cause of a heat blow-off?  Expansion of the wire bead causing
> the bead to release from the hook?  Tire cut?  Other?  Any idea?

There are two main reasons for tire blow-offs, one is overheating
while braking, and the other is that the tube was caught under the
bead when the tire was mounted.  Of course, if you don't have a hooked
bead rim, then normal high inflation pressure is not allowed.

The high temperature blow-off seems to be a combination of effects
that include primarily increased pressure from heating and the
softening and slipperiness of the tire bead that heat causes.  In any
case, enough tandem riders have overheated tires that exploded off the
rim, that it is a known phenomenon.  Because we don't know the
temperature of the air in the tire that exploded, we can't make an
estimate of the pressure.  One thing is certain from my experience and
measurements I have made, is that the rim gets hotter than 120 deg C
and that steam can be generated from water inside a hollow rim.  I
don't know how hot a tandem rim gets.

The creeping blowout that occurs without any exceptional heat, or any
heat at all, is generally the result of a tire that trapped the tube
under the bead on installation.  I have experienced this with "short
tubes" that want to lie in the bed of the rim because they are too
small in circumference.  These have caused blow-offs while parked as
well as when underway.  To test for these, the bead must be pushed
away from the rim wall to assure that the tube is not visible.

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Conti GP blowout
Date: 18 May 2001 16:53:14 GMT

Terry Morse writes:

>>> - Can the Kevlar bead have stretched? (The tyre is very easy to
>>> mount on the rim.)

>> Doesn't matter.  The bead is not what holds the tire on the rim.

> A little clarification: A stretched bead doesn't matter, but it is
> the bead that holds the tire on the rim by hooking onto the bead on
> the inside of the rim.

> Someone (Damon Rinard?) did an experiment to show this by cutting
> the bead of a tire in several places, and it still held pressure
> fine.

That someone was I and Damon repeated the experiment after heated
debate here on wreck.bike erupted when I pointed out that it is
primarily the clinch that holds tires on rims.

The tire blow-off in question most likely occurred because the tube
was between the bed of the rim and bead so that the bead was not fully
seated.  It is this phenomenon that inspired my test of cutting the
wire bead in five places on a worn out tire and inflating it to 100
psi.

Tire blow-offs were common at a time when "short tubes" were being
offered, tubes so short in their major diameter that they lay flat on
the bed of a rim when stretched onto it, preventing proper tire
seating.  Short tubes cost less to make (less rubber) and can be
advertised as being lighter.  To test for this condition, push the
casing back from the edge of the rim to see if the tube is exposed.
The tune should not be visible when the tire sidewall is pushed back.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jobst.brandt@stanfordalumni.org
Subject: Re: 6 or 8 inches front disc?
Newsgroups: rec.bicycles.tech
Message-ID: <dKArb.5534$Wy2.66832@typhoon.sonic.net>
Date: Mon, 10 Nov 2003 00:12:57 GMT

anonymous writes:

>> If you dump too much heat into the system which holds your tyres
>> on, you're going to blow tyres.

> This is pretty unlikely unless you're running at excessive pressures
> already - modern hook bead rims will cope with well over the
> "recommended" pressure before the tyre pops off, and the
> overpressure from a mountain descent is only about 25% [1].  Maybe
> this could be a problem with an 18mm tyre and a wide-ish rim
> starting at 150psi - oops, that describes one of my wheelsets!
> Tubular tyre cement melting on long descents, leading to the tyres
> rolling off in corners, *is* a real problem in the mountains (and
> may account for the unimpressive descending of many pro riders), but
> this applies to a miniscule percentage of non-professional riders.

The problem is not rolling off the rim as is often surmised, but
rather the tire creeping around the rim, piling up against the stem
and either blowing out there or making such a lump that it jams on the
fork crown.  This I have seen and done.  Tubular tires roll mainly
from side slip on loose traction and regaining traction.  Otherewise,
there are no side forces on tires.

Clincher tires at below 100psi can be blown off rims, especially when
descending cautiously.  At high speeds, not much energy goes into rims
because most is taken by wind drag, and rims are better cooled.  I and
fellow riders have all had tire blow-offs, my latest one was a few
years ago while descending slowly, waiting for a friend who was taking
pictures.

> The best rationale I heard for disc brakes was that you could use a
> disc-specific rim with no brake track, so it could be optimised to
> be lighter or stronger, and with no need for surface hardness.
> However, most disc-equipped bikes I see have rims with nicely
> machined surfaces for their non-existent V-brakes ;-)

I don't see that much can be spared in rim weight by that rationale.
How would you prevent people from using them with rim brakes?

> [1] John Forester did a descending test and couldn't even get his
> front rim up to 200 deg F (366K), but if the tyres were filled at 20
> deg C (293K), the pressure at 200 deg F would only have been the
> ratio of the Kelvin temperatures = 125% of the starting pressure.  A
> mountain bike tyre at 40psi is only going to reach 50psi at the
> bottom of a really big mountain.  Not an issue at all.

I have crossed paths with Forester in accident reconstruction law
suits and found his testimony to be based on myth and lore.  I have
little faith in his tests.  I for on have generated steam from water
that got inside tubular tire rims while normally descending a mountain
pass with fast straight sections between hairpins.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: 6 or 8 inches front disc?
Newsgroups: rec.bicycles.tech
Message-ID: <WGDrb.5595$Wy2.66852@typhoon.sonic.net>
Date: Mon, 10 Nov 2003 03:34:14 GMT

Jim Beam writes:

>> I don't see that much can be spared in rim weight by that
>> rationale.  How would you prevent people from using them with rim
>> brakes?

> you don't prevent them.  some shops commonly build disk wheels with
> traditional rims because they're either cheaper or just happen to be
> what they have in stock.  and besides, as you will have seen here on
> r.b.t, some people want dual-purpose wheels.

>>> [1] John Forester did a descending test and couldn't even get his
>>> front rim up to 200 deg F (366K), but if the tyres were filled at
>>> 20 deg C (293K), the pressure at 200 deg F would only have been
>>> the ratio of the Kelvin temperatures = 125% of the starting
>>> pressure.  A mountain bike tyre at 40psi is only going to reach
>>> 50psi at the bottom of a really big mountain.  Not an issue at
>>> all.

>> I have crossed paths with Forester in accident reconstruction law
>> suits and found his testimony to be based on myth and lore.  I have
>> little faith in his tests.  I for on have generated steam from
>> water that got inside tubular tire rims while normally descending a
>> mountain pass with fast straight sections between hairpins.

> who won the lawsuit?

His testimony was easily refuted.  Either he is not aware of the cause
of some bicycle failures or he is prostituting himself for the
plaintiff.  There are such people in the business, like John Howard
and Eugene Sloan and above all, Jim Green of North Carolina whose
testimony I had discredited without knowing what it was, mainly
because he testified against Huffy and Trek using the same evidence to
prove opposite conclusions.  Even Forester finds fault with him:

http://www.johnforester.com/Consult/green_intro.htm

> steam doesn't mean massively elevated temperatures.  my tea is
> steaming right now.

I think you are using the colloquial term for water vapor rather than
steam.  I generated hissing steam (an invisible gas) rushing from the
valve stem hole while braking.  At the heat of vaporization of water,
this requires substantial braking heat in the rim.  Tandem riders and
shops that cater to tandem tourists can tell about many tire blow-offs
reported.  I testified on such a case where the rider was trying to
sue the bicycle shop and rim manufacturer.  That was an easy case once
I saw the evidence.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: HED H3 tire blow off
Newsgroups: rec.bicycles.tech
Message-ID: <amQoc.11091$Fo4.145606@typhoon.sonic.net>
Date: Thu, 13 May 2004 19:52:38 GMT

Carl Fogel writes:

>>> For descending steep roads where the ratio between braking and air
>>> speed (cooling) is poor, such as on rough roads that do not allow
>>> higher speeds than 15MPH, inflation pressure should be kept below 100
>>> psi to avoid tire blow-off.  I often read of tires inflated to
>>> 120-140psi and wonder what sort of steep, hard braking descents these
>>> riders experience, having seen and experienced plenty of blow-offs at
>>> 100+psi on such descents.  Tandems are special cases that should
>>> always have a hub brake to make such descents safe.

>> If a tyre has 100psi at 20C (68F), it need to get to about 80C
>> (176F) to increase the pressure to 120psi. This seems unlikely as
>> the tyre is cooled by conduction to the road surface. As the rim
>> will probably always be hotter than the tyre under braking, thermal
>> expansion shouldn't loosen the tyre fit either. Do you know why
>> tyres blow off on descents? Is there a significant difference in
>> failure rate depending on bead material? Does the valve stem lock
>> the tyre to the rim at one point and the rest of the tyre creeps
>> round the rim due to braking force? Just curious to know whether
>> there is any rigorous research into failure mode and cause.

> I assume that you're using the relative temperatures in degrees
> Kelvin to obtain a 100/120 psi ratio for termperatures 293/353 K,
> which seems to make sense.

> But the absolute effect of heat on gas pressure is greater at higher
> initial pressures. If a 100 psi tire goes to 120 psi, then a tire
> that started out at 125 psi goes to 150 psi. It's only a 5-pound
> difference, but with bicycle tires we tend to feel comfortable about
> 100 to 120 psi, but start to worry when 125 psi rises to 150 psi.

> There may be another heat source. The brake pads heat up the rim on
> a descent, and that's what we notice. But the tire's contact patch
> is braking just as hard against the pavement and also rolling a
> steady bulge through the tire--it squashes out under braking load
> far more than just rolling freely along.

I think you can dump that concept because even a freshly blown-off
tire is not hot to the touch on the tread... or anywhere else.  My
latest experience with that was descending Grosse Scheidegg to
Grindelwald with some of the most famous mountains and glaciers
arrayed in front of me.  My friend stopped to take pictures so I
waited for him riding the rear brake over the lever hood at less than
10mph when BAM! the tire that I had previously ridden over steep
curving descents blew off.  The tire wasn't even noticeably warm as I
changed the tube.  Rubber doesn't gain much heat while rolling, and
even with brakes applied, they aren't skidding or tires would not last
3000miles.

> These descents may also involve stretches of pavement hot enough to
> fry eggs on.  Blacktop sitting in the sun all day is usually much
> warmer than the pleasant mountain breeze.

My experience has been in the mountains where the roads are cold and
often in the shade.  This is grasping for straws.  An inflated tube
pressed against a hot aluminum rim will heat the enclosed air.  Those
who have toured much can verify that this occurs and that tires
blow-off.

> The tire may also act as an insulator, trapping heat.  Car tires
> running at much higher speeds with much higher loads have speed
> ratings related to expected temperatures.  The car tires fail far
> more often in summer temperatures.

I haven't had a car tire fail in so many years that I can't recall
whether I ever had one.  That is not a good statistical model.  I
don't know of any acquaintances who have had flats on their cars
either.

> It's possible that the blow-offs are due not just to higher pressure,
> but also o the tires themselves deteriorating at the higher
> temperatures, the bead material question that you raise.

Why do you try to divert attention from the principal source of such
failures?  This is not a safe thing to do.  People should know that
riding the brake down a hill can cause tire failure and that inflation
pressures as we often hear about here are dangerous for anyone who
rides hills that require braking.

> Thanks for asking an interesting question.

I don't think the answer was any help.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: HED H3 tire blow off
Newsgroups: rec.bicycles.tech
Message-ID: <m7Yoc.11159$Fo4.146300@typhoon.sonic.net>
Date: Fri, 14 May 2004 04:42:58 GMT

Carl Fogel writes:

> Are you suggesting then that the rim heats up from braking, the hot
> rim heats the air insulated by the thin rubber inner tube and any
> rim strip, and the thicker outer tire acts as an insulator,
> remaining much cooler?

It is more than a suggestion.  I have observed enough blow-offs and
talked to tandem tourists who have had to go to drum and disc rear
brakes to avoid overheating the air in their tires.

> That is, where does the heat come from and where does it go?  Is
> just as much energy going into the pavement/contact-patch as into
> the rim/brake-pad patch under steady braking?  Does contact with the
> ground cool the tire significantly?

As I suggested in a related message, next time you are descending a
steep road at speed, bring your bicycle to a stop using the front
brake only and grasp the tire and rim.. carefully, to appreciate the
temperature.

> Your example of a blow-off was at low speed, under 10 mph, but  your
> scenic description didn't specify whether it was the front tire.  (I
> assume so, since that's what does most of the braking and you mention
> riding the rear brake, which might imply no front brake use.).

As I said, it was the rear tire and I merely braked with one hand over
the lever hood keeping the bicycle at just over walking speed as I
waited or my friend.  It never occurred to me that this would blow
off the tire, having descended this road many times without incident
with many others.

> Is this the common scenario, with a hot rim rolling slowly under no
> braking to blow the rim off?

Who said anything about "no braking"?????

> Why does the pressure rise so dramatically after no further braking
> was generating heat?  Or would it have blown off anyway in another
> few moments if you'd kept descending?

> How hot does the rim get and what would the pressure increase be?
> Is the original example of 100 psi rising to 120 psi what you would
> expect?  Would such a rise blow your tires off?

Much more than that.

> I still find Kinky's question interesting and still don't know the
> answer, so I hope that you'll think it through and come up with a
> helpful answer.

You gotta read more carefully Carl.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: HED H3 tire blow off
Newsgroups: rec.bicycles.tech
Message-ID: <Jn8pc.11239$Fo4.147097@typhoon.sonic.net>
Date: Fri, 14 May 2004 18:39:37 GMT

Carl Fogel writes:

>>> Is this the common scenario, with a hot rim rolling slowly under
>>> no braking to blow the rim off?

>> Who said anything about "no braking"?????

>>> Why does the pressure rise so dramatically after no further
>>> braking was generating heat?  Or would it have blown off anyway in
>>> another few moments if you'd kept descending?

>>> How hot does the rim get and what would the pressure increase be?
>>> Is the original example of 100 psi rising to 120 psi what you
>>> would expect?  Would such a rise blow your tires off?

>> Much more than that.

>>> I still find Kinky's question interesting and still don't know the
>>> answer, so I hope that you'll think it through and come up with a
>>> helpful answer.

> "My friend stopped to take pictures so I waited for him riding the
> rear brake over the lever hood at less than 10mph when BAM!"

> Actually, you never do say which tire went BAM! Some of us would
> assume that the front tire is the one that would heat up on a descent.
> We weren't there. The lever hood is a nice detail, but you gotta write
> more clearly, Jobst. (After all, you were surprised.)

Carl, we are talking about brake heating and tire blow-off resulting
from heating the air in the tire.  Descriptions here would get longer
than the unnecessary citation you already include.  I see no ambiguity
in what I wrote and anyone following the thread with attention could
deduce that the rear tire was the only one being heated.  My surprise
came from the light braking I was doing with a hand draped over the
lever hood while creeping along.

> As another example of how easily things may be mis-read, what does the
> end of this sentence mean?

> " It never occurred to me that this would blow off the tire, having
> descended this road many times without incident with many others."

> Many others? What others?

Others means other riders on many rides over the Grosse Scheidegg pass
on bicycle tours in the Swiss Alps on the same bicycle with the same
wheels and similar tires over many years in the past.  Now what did I
leave out?  Oh yes, and descending rapidly and braking hard down the
12+ percent grade with many hairpin turns.

> Many other tires? (Well, obviously. Descending without tires would be
> tricky.)

Your getting warmer.  Keep it up.  I guess Jose Rizel's exchange
knocked your comprehension a bit.  Don't get so testy.

> Other friends? (Seems unlikely, but perhaps the point is that many
> other riders had no tire trouble.)

I'm sure you can come up with an even more distantly related scenario.
You are engaging in what appears to be willful misunderstanding.

> Other brands of tires?  (Possibly, but stretching.)

> You know what you meant, of course, but I don't.  A single word
> would probably clear it up.  Or maybe removing the last three words
> would still say what you meant.  Or it could easily be something
> that I haven't guessed.  Or even just a word processor editing oops.

> Quick writing about vivid events is often like this--we can't believe
> that the reader failed to follow us, while they're left wondering what
> on earth we meant.  You can't imagine how I could think it was your
> front tire, while I can't figure out which one you meant.

Well how about explaining why a front tire would blow-off the rim with
only the rear brake applied.  If you followed that concept I think you
would come upon the fact that the rear tire came off.

> Leaving clarity theory aside, you say that it never occurred to you
> that this would blow the tire off.  So what's the explanation?  I seem
> to recall that you've suggested that prolonged low-speed braking is
> worse than high-speed descent because there's less air cooling of the
> rim, but I may have misunderstood you.

You may have taken from what I wrote that all slow speed braking can
cause tire blow-off yet you suspect my front tire came off.  I thought
the heat input to the wheel at such low speeds would not cause
overheating but it reinforced my appreciation for the effects of air
cooling loss at low speeds.  This is much like riding next to a friend
who is walking down an RR underpass sidewalk while lost in
conversation.  Fortunately such descents are too short but they are
steep enough and at low speeds that we regularly find innocuous, tire
blow-off can occur.

> Was this a prolonged low-speed descent?  You say that you'd slowed
> down for a friend, but for how long?  A minute or so?  Ten minutes?
> A hundred yards, half a mile, a thousand feet of altitude?

For about 200 meters distance.  The point is that this example in
particular underscores the heat generated and loss of cooling.  That
was the point of mentioning it so others don't believe that slowing
down will prevent this.

> And where does the heat generated at the tire's contact patch go on
> a long descent with heavy braking?  Into the pavement?  The tire?
> Dissipated into the air?  Or am I mistaken about as much heat being
> generated at the contact patch as at the brake pad?

There is no perceptible heat at the contact patch.  As I mentioned. if
there were, tires would wear out in a short time.
Heat can be derived from the RR tables shown here often:

http://www.terrymorse.com/bike/rolres.html

You can compute the work of pushing a few grams times speed.  RR
losses are energy that goes into heat.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: HED H3 tire blow off
Newsgroups: rec.bicycles.tech
Message-ID: <aIPoc.11078$Fo4.145562@typhoon.sonic.net>
Date: Thu, 13 May 2004 19:07:50 GMT

anonymous snipes:

>> For descending steep roads where the ratio between braking and air
>> speed (cooling) is poor, such as on rough roads that do not allow
>> higher speeds than 15MPH, inflation pressure should be kept below
>> 100 psi to avoid tire blow-off.  I often read of tires inflated to
>> 120-140psi and wonder what sort of steep, hard braking descents
>> these riders experience, having seen and experienced plenty of
>> blow-offs at 100+psi on such descents.  Tandems are special cases
>> that should always have a hub brake to make such descents safe.

> If a tyre has 100psi at 20C (68F), it need to get to about 80C
> (176F) to increase the pressure to 120psi.  This seems unlikely as
> the tyre is cooled by conduction to the road surface.  As the rim
> will probably always be hotter than the tyre under braking, thermal
> expansion shouldn't loosen the tyre fit either.  Do you know why
> tyres blow off on descents?  Is there a significant difference in
> failure rate depending on bead material?  Does the valve stem lock
> the tyre to the rim at one point and the rest of the tyre creeps
> round the rim due to braking force?  Just curious to know whether
> there is any rigorous research into failure mode and cause.

Descending a mountain pass with a series of hairpin turns after having
descended snowfields and crossing creeks while approaching the first
hairpin turn I noticed that I had a leak in my front tire by the
hissing pss-pss-pss... as the wheel rotated.  Since it wasn't flat yet
I continued after the turn to find a good spot to fix the tire and
noticed that it had not lost significant air and was no longer audibly
leaking.  After repeating that routine a couple of times, I braked to
a stop on a straight section and found that what I heard was steam
coming from around the stem, the only place where it could escape
easily.

This event makes clear what temperatures are generated and how fast
they rise and fall while and after braking.  As I said, I have
observed blow-offs on my own bicycle from braking and ones on riders
with whom I rode in areas where this presents a problem.  If you need
more information on this, talk to tandem tourists who have descended
the Alps.  I have been involved in a blow-off tandem law suit where
the rider claimed the rear wheel was faulty and that is why the tire
came off even though he used only the rear brake after a longer ride.

On such rides I also discovered how poorly rim brakes work when wet,
wetter than when riding in rain.  With snow packed on the rim inside
circumference, even moderate braking returns only after all snow has
melted from the rim.  A continuous water supply to the braking surface
reduces braking to near nothing, something that is not apparent when
just riding in rain where only partial wetting of the rim occurs.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: HED H3 tire blow off
Newsgroups: rec.bicycles.tech
Message-ID: <rOXoc.11150$Fo4.146191@typhoon.sonic.net>
Date: Fri, 14 May 2004 04:20:39 GMT

Alfred Ryder writes:

>> Descending a mountain pass with a series of hairpin turns after
>> having descended snowfields and crossing creeks while approaching
>> the first hairpin turn I noticed that I had a leak in my front tire
>> by the hissing pss-pss-pss... as the wheel rotated.  Since it
>> wasn't flat yet I continued after the turn to find a good spot to
>> fix the tire and noticed that it had not lost significant air and
>> was no longer audibly leaking.  After repeating that routine a
>> couple of times, I braked to a stop on a straight section and found
>> that what I heard was steam coming from around the stem, the only
>> place where it could escape easily.

>> This event makes clear what temperatures are generated and how fast
>> they rise and fall while and after braking.  As I said, I have
>> observed blow-offs on my own bicycle from braking and ones on
>> riders with whom I rode in areas where this presents a problem.  If
>> you need more information on this, talk to tandem tourists who have
>> descended the Alps.  I have been involved in a blow-off tandem law
>> suit where the rider claimed the rear wheel was faulty and that is
>> why the tire came off even though he used only the rear brake after
>> a longer ride.

> Would you be kind enough to give a little more information on the
> mechanism for the blow-off?  I understand that heavy braking causes
> the rim to get very hot.  But is it simply the increased air
> pressure that blows off the tire?

Yes.  That's it.  Having had such occurrences and having replaced the
tube in the same tire to continue riding for a long distance
thereafter, I am sure there is nothing else significantly involved.
In fact once two of us were descending a steep dirt road at the same
speed except that my friend had that morning inflated his tires to
just over 100psi while mine were no more than 100psi (I'm also the
heavier rider).  His tire blew off, probably because he was not as
careful to use both brakes as I was, because I recognized the descent
as a heating hazard while he did not, not having had this experience
before.

> How high does the pressure have to get before a tire blows off?  I
> could try it by putting a couple of cartridges of CO2 in a wheel
> but, for some reason, don't feel like it.  Would a steel bead keep
> it on better than a composite bead?

No.  As I explained, the tire is held in place by the clinch, not the
constriction of the bead wire or Kevlar.  Besides, All the tires I
have witnessed blowing off were steel beaded tires.

> Is it possible that differential thermal expansion is a contributing
> factor?  I know that rubber and some composites have relatively high
> coefficients of thermal expansion.

Try grasping your wheel after a hard stop on a steep grade and beware
that you will burn the skin off your fingers if you do so.  Rims cool
amazingly fast as soon as the bicycle is allowed to coast above 20mph.
It is even faster if there is water in the rim, but even that reaches
boiling temperatures rapidly.

> I had a blow-off only once and that was just after a panic stop at a
> stop light.  I could not believe how loud it was.

Yes, it is convincing.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: HED H3 tire blow off
Newsgroups: rec.bicycles.tech
Message-ID: <3%Xoc.11156$Fo4.146107@typhoon.sonic.net>
Date: Fri, 14 May 2004 04:34:07 GMT

Jay Beattie writes:

> Sounds like an argument for disk brakes.

Interesting that you bring that up.  I am unwilling to load my bicycle
with the extra weight and complexity to try it but I have considered
the heat I have observed.  I cannot imagine that the typical disc we
see on bicycles today, weighing only a few 100 grams, can absorb the
energy required without collapsing and initiating brake failure.  A
crumpled disk is a certain endo that I am unwilling to test, even if I
were offered such a bicycle before a descent.

The flimsy perforated disks offered today are a mere lacework of thin
steel that is easily deformable at room temperature and easily
collapsible at yellow heat, which it would achieve on descending roads
I have encountered on my rides.

In the summer:

http://www-math.science.unitn.it/Bike/Countries/Europe/Tour_Reports/Tour_of_the_Al

now:

http://jpeg.popso.it/webcam/webcam_online/image11.jpg

Note that this CAM is 9hrs earlier than PDT or 6hrs from EDT.

The plows have finally come.  The Giro d'Italia is due soon so the
road must be open here and over the Gavia.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: HED H3 tire blow off
Newsgroups: rec.bicycles.tech
Message-ID: <qsBpc.11465$Fo4.149672@typhoon.sonic.net>
Date: Sun, 16 May 2004 03:44:22 GMT

Pook who? writes:

>>> Sounds like an argument for disk brakes.

>> Interesting that you bring that up.  I am unwilling to load my
>> bicycle with the extra weight and complexity to try it but I have
>> considered the heat I have observed.  I cannot imagine that the
>> typical disc we see on bicycles today, weighing only a few 100
>> grams, can absorb the energy required without collapsing and
>> initiating brake failure.  A crumpled disk is a certain endo that I
>> am unwilling to test, even if I were offered such a bicycle before
>> a descent.

>> The flimsy perforated disks offered today are a mere lacework of
>> thin steel that is easily deformable at room temperature and easily
>> collapsible at yellow heat, which it would achieve on descending
>> roads I have encountered on my rides.

>> In the summer:

http://www-math.science.unitn.it/Bike/Countries/Europe/Tour_Reports/Tour_of_the_Al

> When I first arrived in Colorado, I rather foolishly decided to go
> to Winter Park, ski resort and take my bike up the ski lift and
> cycle down.  Now I considered myself to be a reasonably good MTB'er
> but quickly found myself out of my depth; the trail being both
> extremely steep and rocky (as in large rocks) After a semi-nasty
> fall, I lost my nerve, and descended the rest of the slope v.slowly
> indeed.  Definitely slower than 10mph.  My bike was equipped with
> hydraulic disk brakes: Magura Julies.  At no point did they fail,
> indeed my controlled descent never required more than one finger.

That still doesn't assure me that the disc will not fail mechanically
on a hard descent.  Riders have reported bright red discs at sunset and
knowing that, I am sure I would see yellow glow, judging from the
demands that I put on brakes on my road bicycle.  It was not for
nothing that I devised epoxy heat insulators for my tubular tires on
descent that others told me were no problem although I could
completely melt rims glue and explode tires on them.

> Subsequently I've ridden the same trail at much higher speed as I
> became more competent, with no problems.  Now I'll happily admit
> that they look spindly, but I've never heard of disks collapsing as
> you suggest, although a friend reports his XT disk brakes fade on
> this run, but this is a pads issue I surmise.  Has anyone heard of
> the disk itself buckling (not just warping slightly), and indeed
> actually seen said item?

I'm concerned that it soften and wrinkle, locking up the brake.  Fade
or a little wobble is not a crash worthy problem but disc collapse is.
As I said, my rims get hot enough entering turns to generate plenty of
steam with rim brakes.

> This may sound perverse, but I've knowingly tried to see if I could
> get the rear disk to 'fade' but to no avail.  I've tried this on
> roads/trails that I believe are as steep as those to which you
> refer, i.e >12% (cf. bottom part of Magnolia Rd, off Boulder
> Canyon).

As I said, fade is not as serious a problem as disc collapse.

> I'm not averse to your supposition, but my practical experience has
> not borne this out.

> A couple of side-notes:

> The disks on my bike are the standard stainless steel 180mm/190g
> front and 160mm/155g rear.  These seem to be significantly larger
> than most: Shimano XT (2003 model without separate spider) are
> 160mm/140g FRONT!

> I weigh 70kg.

> On my descent at Winter Park they did ooze fluid out the reservoir
> as they heated up to such an extent.  Now the reason for this I
> believe is that Magura and Shimano both use mineral oil, instead of
> DOT fluid.  I can't imagine that would have happened if DOT fluid
> had been spec'ed.

So I weigh 90kg and brake from 70kmh to essentially zero on successive
hairpins, or continuously on 20% and steeper roads.  Austria and the
Dolomites are full of such roads.

> I don't see the benefit of disks out in Colorado as there's no mud
> to speak of, however in the UK they're the single best thing to have
> happened to MTBs IMO; I'd never go back, to the massive drag of
> clogged rims/brakes and the 'disappearing' act that rims and pads do
> in such conditions.

The smooth and continuous brake response is worth the difference if
it is reliable.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: HED H3 tire blow off
Newsgroups: rec.bicycles.tech
Message-ID: <KN8pc.11243$Fo4.147140@typhoon.sonic.net>
Date: Fri, 14 May 2004 19:07:22 GMT

Bill Kellagher writes:

> What's up with these rims??  Why do they fail to hold tires?

> Here are a few details/observations:

> In mounting the tires, I was very careful to avoid tube inclusions.
> After mounting the tire, I slightly inflated the tube and went round
> the entire rim pulling the tire back a bit to make sure the tube
> wasn't sitting under the bead.

> In inspecting the rim for damage, I noticed that these rims are NOT
> hooked.  The rim flanges are straight, and do not have the usual
> bulge to the inside that I would expect.

I wouldn't ride a mile on a non-hooked bead rim.  My Kevlar bead tires
blow off smooth side rims at about 90psi.  This is not my idea of a
reasonable rim.  I've never seen them and don't advise anyone to use
them.  High pressure clinchers were made possible by the hooked bead
rims.  Before that one had to ride tubulars to get high performance.

> Also, the rim flanges are not very tall.  I did not measure, but the
> distance between the rim floor and the top of the the flange is much
> smaller than other rims I have seen.

These guys deserve to be sued for offering a faulty product.  This is
a hazard in its worst form.  One that typically gives no warning
before causing a fatal error if, for instance you are approaching a
curve at a precipice or an intersection with heavy traffic.  Where do
these guys get such weird notions after years of high performance
hooked bead rims offered by rim manufacturers.  What is their point?

On their web site:

# Lance uses these on the front of the TT bike. I have the same 2002
# USPS Frameset with the H3's. One this bike, there are like knife
# blades slicing into straight-on head winds. Yet, when a stiff cross
# wind, or a large van, SUV, or truck pass you in the same direction,
# you need to be prepared to have the front of the bike dive into the
# negative pressure created by the vehicle. Just have to grip extra
# tight for a few seconds until the pressure comes back up.  I have
# the Rolf Vector Pros and the H3's. On the same day, within 10
# minutes of each, I let gravity pull me down a 1/2 mile hill on each
# set of wheels. Here are the results:

# TT Bike with Vector Pros...27 MPH MAX (coasting only)
# TT Bike with HED H3's......33 MPH MAX (coasting only)

# As you can see, they are unreal! Worth the bux! $900.00 range for
# the pair.

# Posted by Joe Rafferty
# LawyerJoe.com

There are more things amiss in this testimonial than omissions.

Power is Velocity cubed on a bicycle so knowing that a trained rider
working hard can ride 25 to 27 mph or the equivalent of 27**3 = 19683
while 33**3 = 35937 or 35937/19683 = 1.826, nearly twice the power,
and this is a result of the wheels.  Consider that the comparison
Rolf wheels are already low spoke count wheels that make unbelievable
claims for themselves.  I don't believe a word of it.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Exploding flats - BLAM! Blowout.
Newsgroups: rec.bicycles.misc
Message-ID: <Ha6L9.54848$Ik.1632154@typhoon.sonic.net>
Date: Sun, 15 Dec 2002 21:07:51 GMT

Mark Benson writes:

>> The second occurrence sounds more like a pinched tube, a place
>> where the bead was sitting ON the tube at the edge of the rim.
>> This is also exacerbated by temperature and braking forces that act
>> as a massaging function to allow the tire bead to creep off the
>> rim.

> This type of problem can sometimes be caught before it becomes a
> blowout.  If, after fixing a flat, your wheel suddenly has a "hop"
> to it, the bead is not properly seated and the tube will "blow out".

That's where I became familiar with the problem many years ago,
however, I got off grabbed the place where the tire was lifting off
but could not get the valve open in time before the tube blew out
under my grip.  The lump-lump-lump got bigger as I braked to a stop.

Jobst Brandt  <jobst.brandt@stanfordalumni.org>  Palo Alto CA

From: jobst.brandt@stanfordalumni.org
Subject: Re: Tyre Pressure
Newsgroups: rec.bicycles.tech
Message-ID: <bhbxa.14752$JX2.893108@typhoon.sonic.net>
Date: Fri, 16 May 2003 19:49:27 GMT

Per Elmsäter writes:

>> Fat tires may not be as susceptible to over heating as road bicycle
>> tires, but this is my primary concern, having blown tires off from
>> severe braking.  The blow-off pressure is dependent mainly on the
>> rim width at the bead, that being the effective cross section for
>> pressure induced blow-off force.  For this reason, it is my
>> experience that no more than 100psi is the safe limit for
>> descending steep roads that require much braking.  This won't be a
>> problem for fat tires because they don't run that high.  Their
>> problem lies in casing failure.

> Does that mean the pros inflate their tires to sub 100 psi pressures
> on steep mountain stages?

I don't know what they do but the pursuit of 140psi inflation even on
flat runs is useless, rolling resistance of racing tires being
insignificant at 100psi.  Few mountain passes require braking that
would be a hazard, there usually being long enough straight sections
to cool rims.  Steep dirt roads are no longer part of major races and
these often required continuous braking.

I generally don't ride more than 100psi because my rides occasionally
require steep descending such as the Idria ride posted on
wreck.bike.rides recently.

Jobst Brandt
jobst.brandt@stanfordalumni.org
Palo Alto CA

From: jobst.brandt@stanfordalumni.org
Subject: Re: Disc brakes on tandems?
Newsgroups: rec.bicycles.tech
Message-ID: <mu6Qd.6779$m31.82347@typhoon.sonic.net>
Date: Mon, 14 Feb 2005 18:55:14 GMT

David Damerell writes:

>> Couple of questions for setting up disc brakes on our tandem.

> I'm curious to know why you don't want to use rim brakes and a drum
> brake.

Unless you've blown a tire off a rim from braking, the reason is less
apparent.  Tandem tire blow-offs are well known.  I have experienced
them on single bicycles as well and am aware of fatalities on local
descents that I am certain resulted from such an occurrence, there
being no other reasonable explanation for the crashes.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Disc brakes on tandems?
Newsgroups: rec.bicycles.tech
Message-ID: <4tbQd.6816$m31.84126@typhoon.sonic.net>
Date: Tue, 15 Feb 2005 00:35:12 GMT

Pete Cresswell writes:

>> ... and am aware of fatalities on local descents that I am certain
>> resulted from such an occurrence, there being no other reasonable
>> explanation for the crashes.

> That's an interesting observation.

> When I lived on the island of Oahu a looooong time ago, one of the
> things that struck me was that a cyclist was killed on something
> called the Likelike Pali about once every month or so.

> At the time I just figured it was a bad traffic mix.

As I mentioned in this regard previously, there are a few major roads
in the Alps where bicycling downhill is prohibited for that reason.
An especially famous one is the Zirlerberg between Garmisch and
Innsbruck.  It has six runaway exits for cars and trucks:

http://www.sagen.at/texte/gegenwart/oesterreich/tirol/allgemein/picknickamzirlerbe

> But the descent into the town on either side of this
> sort-of-mountain is *really* steep and long...  Now I've got to
> wonder if people were losing front tires on the descent.

The incidents here on Hicks and Metcalf roads were passed off as "too
much speed" something that anyone astute in accident reconstruction
could easily show that the tire blew off.  If the rim has pavement
scrapes on its periphery it had no tire on it before the crash.  The
report of the most recent Hicks road fatality had the condescending
tone toward an irresponsible bicyclist speeding out of control.

On the other hand, I don't want to see these roads closed to
bicyclists, only that riders are made aware of the hazard of
descending steep grades.  I ride there on occasion and am careful to
distribute braking to both wheels and to not exceed 100psi inflation
pressure.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Disc brakes on tandems?
Newsgroups: rec.bicycles.tech
Message-ID: <uerQd.6936$m31.86931@typhoon.sonic.net>
Date: Tue, 15 Feb 2005 18:31:54 GMT

Bill Bushnell writes:

>> The incidents here on Hicks and Metcalf roads were passed off as
>> "too much speed" something that anyone astute in accident
>> reconstruction could easily show that the tire blew off.  If the
>> rim has pavement scrapes on its periphery it had no tire on it
>> before the crash.  The report of the most recent Hicks road
>> fatality had the condescending tone toward an irresponsible
>> bicyclist speeding out of control.

> Were the bicycles in question examined for evidence of blowoff?

I don't believe so.  Otherwise there would have been a different tone
to the reports of these incidents.

> I descended the west side of Metcalf on Saturday and found the
> pavement in poorer condition than on Hicks, especially in the corners
> where "asphalt moguls" had been raised and gravel from a cheap tar &
> gravel job had been sloughed off leaving slick tar exposed.  A little
> moisture on the road could make it dangerously slick.

The incidents I am referring to occurred in summer.

Jobst Brandt
jobst.brandt@stanfordalumni.org