From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Gluing Tubulars - A question
Date: 11 May 1999 00:08:24 GMT

Doland Cheung writes:

>> The only technical disadvantage is that, on long descents where you
>> have to brake extensively, some glues can soften to a dangerous level.

> Which glues are these?

All pressure sensitive glues.  That means any glue that is sticky, in
contrast to epoxy or shellac that gets hard and does not melt.
Besides, some people have mentioned that they descend "carefully"
rather than hot-rodding down mountains.  Riding less than maximum
speed puts more of the descending energy into heat in the rims that
blowing it away in wind drag.  This became obvious to me when my young
son rode down some hills (where I had not had tire creep previously)
ahead of me as I followed slowly with my brakes on.  This caused the
glue on my rims to melt and shift the tire.

As I described on my first bike tour in the Alps, I blew out several
tires because repeated hairpins require full stops and dirt roads of
that era required slow descending.  None of this 40mph stuff.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Tubular vs Clincher
Date: 7 Aug 1999 00:28:46 GMT

Steve Freides writes:

>> However, tandems require an auxiliary brake for descending mountains
>> anyway to prevent excess rim heating and tire blow-off.  Even single
>> bicycles heat problem on steep roads where all descending energy
>> goes into the rims, either because the road is too windy to go
>> faster or the road is to rough or loose to safely let it roll.
>
>This topic has been under discussion on the tandem list of late.  Many
>tandem riders, myself included, do not use or even own a drag brake.
>I don't ride in mountains living here in North Eastern NJ but it is
>hilly in places and a drag brake has never been necessary.  Apparently
>quite a number of tandem teams feel equally comfortable without the
>drag brake.

Its not a matter of whether you feel comfortable.  Its a matter of
blowing a tire off the rim, probable at the least favorable location
like in a right hand curve with oncoming traffic.  That this happens
is not disputable and its cause is understood.  I have blown tires off
on steep roads on my single bicycle as have others.  Tandems that
descend where breaking is demanded do this also.

>I don't know if it helps me, but I use my brakes in an on-and-off
>fashion when I need them on descents, applying them for what seems
>like a second or two, then leaving them off for longer than that.  It
>seems, subjectively, to reduce heat-induced brake fade.  I discovered
>this technique while driving a borrowed car one day many years ago
>that had, it turned out, very poor brakes.  I credit it with allowing
>me to reach the bottom of the hill without having an accident.  It was
>the only way the brakes would actually slow down the car (a 1965
>Impala if memory.

Your comment makes me think of Jeff Steinwedel, a local rider here,
who wrote on rec.bicycle.misc assuredly the week before his murder by
a trucker, that he had a good understanding with the truckers and
waved to them as they passed.  You are whistling in the dark if you
think you can prevent a tire blow-off by pumping the brakes.
Alternating the brakes between front and rear is a good method of
accurately dividing the effort between the front and rear wheel, but
if the grade is steep enough, the energy dissipation will exceed the
safe temperature of tire retention.

On the other hand your hills may be insignificant and no matter what
method you use your tires will remain safe.  I don't know these hills
but if you've been doing this for a while they can't be as demanding
of brakes as 8%+ winding roads.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.misc
Subject: Re: Dark art of descending!
Date: 23 Aug 1999 22:03:22 GMT

Jeff Potter writes:

> Going down the top super steep half was like doing a pushup! I had to
> brake full-on on the straights not to go too fast for the curves.
> Tired hands.  SUPERHOT RIMS!  I had sewups on, so I stopped for a
> few minutes halfway down.

> How do you guys deal with superhot rim heating? Is there such
> a thing as too steep?

I don't know how you kept the tires from slipping on the hot glue and
piling up on the stem.  This is the usual indicator that tubular tire
wheels are too hot.  The next is that the tire lifts off in the
compressed area just ahead of the stem.

This is a serious problem both for tubulars and clinchers because most
clincher tires, given enough heating time on a hot rim will blow off
if inflated to the hardness that most racers like for criteriums
(hard).  The faster you can go, the more power goes into wind drag and
the more air rushes over the rims.  Slowing down does not help, unless
you reduce speed to a walking pace.

For steep descents where the rims stay hotter than you can bear to
touch for more than a minute, you should let some air out of the tires
to where you would normally want to re-inflate them after some disuse.
I don't mention a pressure because that depends on the tire size.
Small tires heat up faster than large ones but the blow-off pressure
is the same, it being dependent only on the opening of the rim width.

> I felt I was going too fast for the curves yet it was too steep to
> slow down enough! Well, that was when I was 'rawest,' I got a lot
> bolder at the halfway down point.  It was fun to start throwing the
> body into the turn, to point the shoulders out to the exit of the
> turn, all over again. Kind of point the body, then pull the bike
> around.

All that "body English" is gratuitous gesture, much like the
motorcyclists who stick their butt out in curves while their bikes
never get down to 45 degrees (where hiking out becomes necessary to
keep hardware from dragging on the road).  In fact, if you are taking a
bunch of ess bends rapidly, you'll have no time to change your
position.  Just keep your weight on your (horizontally positioned)
feet, and unless the road is rough, keep light pressure on the saddle.

> The other good rule was: make half your turn by the halfway point!

I disagree, because you can slow down much faster than you can
accelerate.  The trajectory is naturally asymmetric.  And you can
brake all the way to the apex of the curve, but you cannot pedal at
that lean angle.

> The other good rule was: make half your turn by the halfway
> point!into the turn you're already throwing yourself down and to the
> inside and looking to the far straight, you twist your shoulders
> toward the center of the turn. It feels like you're getting yourself
> all oriented to the exit even before you've gone in!

That may look impressive but it doesn't have any positive effect on
the lean of the bicycle and its traction on the road, that being what
counts in order to corner at the limit.

> Does this at all relate to a correct way to handle switchback descents?

The term switchback refers to mountain railroading where at the end of
each traverse, a switch is turned to back up the next traverse, after
which another switch is turned to head up the next traverse.  The
appropriate term is hairpin turn and these are the ones where
trajectory asymmetry is most conspicuous, because braking can be hard
enough to raise the rear wheel when entering but one cannot accelerate
similarly.  Most riders often find themselves with extra unused road
on the exit of such turns.  This exemplifies the difference between
entry and exit of turns.

> Does anyone descend the top half of Flagstaff without much braking?

I'm not familiar with that road but there are many that have gradients
that requiring stops to cool the rims.  There is no way of descending
them continuously unless you have insulators between the tube and rim.
Insulating rim strips are no longer offered because they were an
artifact of dirt roads that required riders to descend so slowly that
all potential energy went into the brakes and almost none into wind
drag.  These rim strips were cloth tubes filled with kapok, their
insulating purpose being a mystery to most riders when they were last
offered.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Max pressure, was Re: Does tube size matter????
Date: 7 Nov 1998 20:07:32 GMT

Matt O'Toole writes:

>> There is a critical pressure below which the tire will stay on and
>> above which it will come off, especially if ridden.  Riding works
>> the rim contact such that it will creep off.  That is why tires
>> have special chafing cloth on that part of the bead.

> How does this critical pressure relate to what's stamped on the
> sidewall?  Is there some kind of industry standard safety margin?
> Is it a really bad idea to exceed the manufacturer's
> recommendations, or can you safely push it a bit?  How much?

Only to the degree that the manufacturer thinks there is a margin of
safety.  I ride my tires above that number knowing that I should not
make any steep descents that require long periods of braking unless
the pressure is near 100psi, not 120psi, which is close to the limit.
Both pressures are above the recommended if I recall.

> I used to run my Conti Avenue slicks at 80 psi, because they felt faster
> than at the recommended max of 65.  A mountain bike with fat slicks is great
> fun for descending steep, twisty mountain roads, more like riding a sports
> motorcycle than a bicycle.

A fat tire takes a long while to get too hot, there being lots of air
and only a narrow strip of contact with the rim that is hidden behind
the rim tape.  As I mentioned, in the "olden days", insulating rime
tapes made of cloth tube filled with kapok were available for touring
bikes that rode in the mountains.  No one knew what they were for and
so they disappeared.  We were riding tubulars at the time and had our
own problems of rim glue becoming liquid at elevated temperatures.

> Perhaps it's too confidence inspiring: going so fast and deep into
> the corners, braking so hard, the rims get pretty hot.  I always let
> some air out beforehand, just in case.  I've never blown a tire off
> doing this, but . . . could I?

What's important is how long you keep the rim hot.  It's surprising
how fast a rim cools off after a hard application.  You can try this
by stopping on a steep descent and feeling the rim before rolling into
a dip with an uphill on which you can stop again and feel the rim.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: tubulars and long steep descents
Date: 2 Sep 1999 17:44:36 GMT

Brian Nystrom writes:

>> All pressure sensitive glues are thermally sensitive.  If you want a
>> glue that permits tire changes on-the-road, you're stuck with a
>> thermally sensitive glue.  Cured glues won't re-stick.

> Thanks for the clarification, Jobst. Have you seen any data comparing
> relative heat sensitivity of various glues?

No but I am sure there is a wide spread.  Nevertheless, I found that
none was good enough to descend steep dirt roads in the alps because
speed was not an alternative, all energy went into the rims, the road
bing too rough to get up any wind drag.  Recently I descended some
steep paved roads at more than 15% that required stopping to cool
rims with clinchers.  The rims were sizzling hot and I was not about
to let the air out of my tires only to pump them up again in a short
time.  That is an alternative.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: tubulars and long steep descents
Date: 2 Sep 1999 23:53:10 GMT

Tomas Jonsson writes:

> Could you put your engineer hat on and define "sizzling hot" in
> units?  Degrees centigrade would do adequately.  Seems to me the
> Universal Gas Law is adequate to apply here to see if your tires
> were really in danger of blowing out.

What do you mean by "really"?

I don't know other than that tubular rims that I rode that had water
in them from a creek crossing repeatedly caused hissing steam as I
braked for hairpin turns on the Nufenen pass, a pass noted for its 10%
grades.  If you are conversant with gas laws you probably also know
that water has a heat of vaporization of 450 Cal/degF, that is ample
to heat a rim to far more than 212 degF needed for steam.  I know that
the rims are too hot to touch and that it is plenty to melt any
pressure sensitive glue I have used, including Fastack.

> I have routinely over pressured my tires on my tandem above the max
> stated on the sidewall ( I've put 120-130 psi in tires that state
> 100 psi max using 27" Superchampion 48 hole rims) and not had a
> problem under my usual riding circumstances (not steep downhills
> with a lot of heavy braking on the rims as I have a disk brake on
> the rear to control speed).

I know that I and others with whom I ride have blown off tires with
prolonged descents and that tandem riders who have descended the alps
on roads with series of hairpins have done likewise.  Locally, I have
testified in cases where riders spoke as you do and insisted that
their blow-offs were caused by the wheel builder and the tire producer.
I take it you don't believe tires blow off from braking.  Could you
expand on why you are sure of that?

> Perhaps you have knowledge of the design safety factor for tire
> pressure used by the manufacturers.  I would think it would be a
> factor of 2 at least under no load circumstances.

I think you are assuming this and have no idea what it takes to
achieve such a safety factor.  The tires we ride are in fact clinchers
almost exclusively at pressures over 100psi.  I have cut the wire bead
of a 700-28 clincher at 5 places, mounted the tire and inflated it to
100 psi without the tire dislodging.  Higher pressure cause the tire
to fail at the cuts.

> I calculate that if the air in your tires went from 22 deg at 100
> psi to 127 deg C.  (well above water boiling temp) the pressure
> (with insignificant volume expansion) would increase to 136 psi.  Is
> that enough one should worry?

Yes.  In fact the increase in pressure before blow-off is not noticeable
in ride quality.  That is why one does not notice that pressure is
rising above critical.

> At what multiple of the stated sidewall pressure should one begin to
> be concerned.  I know that the rim condition and design play a
> factor, but foolishly assume that good, relatively new rims should
> not seriously compromise your confidence.

The rim condition plays no role unless you mean worn through
sidewalls.  As I have mentioned, formerly insulating rim tapes made of
bias weave cloth tube filled with kapok were available, when I was
still riding tubulars.  No one knew why one should use such base tape,
but now I know.  At that time few hooked bead rims were available and
tire blow-off was more common.  We could do well with such insulators.

By the way, the blow-off pressure is independent of tire size because
only the cross section of the rim gap affects this.  Therefore the
smaller the tire the faster its air will heat up to dangerous
temperatures.  I for one do not inflate my tires to 120 psi when I am
planning to descend big hills where I'll be on the brakes
continuously.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Water in Wheel
Date: 15 Aug 2001 23:46:30 GMT

William Burrow writes:

>> It was raining again for my Sunday ride and I got water in the rear
>> wheel again.  How does it get in?  Spoke nipples look dry so I
>> assume it must get in thru the valve stem hole.  Is this
>> preventable?

> What do you mean, you "got water in the rear wheel"?  Water won't
> make it past a properly inflated tire and tube, even if immersed in
> water (e.g. a stream or similar).  Elaborate.

Light weight rims are hollow extrusions and are not sealed at the
valve stem hole, or for that matter only poorly sealed at the spokes.
It was this fact that first made me aware of transient rim
temperatures from braking on a long descent with many hairpin turns.

I had crossed spring snowfields and a creek from which my rims had
apparently collected water.  Braking on the descent caused steam to
come hissing around the valve stem so loud that I though I had a flat,
only to notice that after the curve the tire was still hard with no
'leak'.  After a couple of these I saw that it was steam and that soon
there was none as the rim dried out.

The reason this was interesting to me is that I was riding tubulars in
those days and wasn't aware how hot rims get from braking and that rim
glue got soft enough to let the tires creep.

Jobst Brandt    <jbrandt@hpl.hp.com>

From: jobst.brandt@stanfordalumni.org
Subject: Re: Potential good news for Mt. Washington access.
Newsgroups: rec.bicycles.misc
Message-ID: <1gIDd.693$m31.7748@typhoon.sonic.net>
Date: Sat, 08 Jan 2005 03:16:13 GMT

Matt O'Toole writes:

>>> Mountain bikers ride fire roads like that all the time.  The
>>> mountains of the western US are riddled with them -- 4000' climbs
>>> at over 10%, sometimes over 15%.  Rims get hot, but not enough to
>>> blow tires.  So I don't see what the big deal is.  There are a
>>> bunch of roads around here with sustained grades like that, but
>>> nothing that long -- 2-3 miles at most.

>> I'm unclear on what you are proposing.  Do you mean that tires do
>> not blow off rims from brake heating?  As a counterpoint, I have
>> had two of these occurrences and have witnessed many more.

> Of course this happens.  I've seen it too, but it's not common.  I
> don't think there are too many hills in the US where this is likely
> to be a problem, Mt.  Washington included.  Like I said, I've ridden
> many hills of similar steepness and length for many years, and never
> heard of anyone blowing tires off.  The Alps are another story, with
> 2-3 times the vertical relief of most mountain ranges in the US.
> How big and how steep a drop does it take to blow a tire off anyway?

I think you don't understand the problem.  A steep section of 200
yards is enough to blow off a tire if only one (typically the front
one) rim brake is used.  I have done it and so have others.  If only
one in a hundred riders has such a failure and suffered serious injury
or death, as it has on local roads, all hell would break loose.

You may have seen pictures from Sonora Pass in California with its 26%
warnings.  It has a few longer runs of 18% but these are straight and
require no braking until the next turn.  These turns are mostly not
extra steep and I know of no one who had a tire blow-off on this pass
that is equally steep on both sides.  I can imagine that it has
occurred, but not in any of the rides I have seen.  In contrast, I
have seldom exceeded 50mph on this road because it is intermittently
extra steep and it has many curves where all speed is lost.

In contrast, a 13% grade on the Fedaia Pass and a 15% section of the
Rombo pass guarantee 60mph.  Neither of these roads is a major hazard
to descending although the Rombo has a bicycles prohibited sign on
ascent of the Italian side.  The steep descent is on the Austrian
side.  The cavalier attitude to this hazard is classic of the machismo
in the USA and therefore no one will assess the hazard it being non
existent in the minds of bicyclists.

>> I think the management doesn't want the contention for road space
>> between bicycles and cars.  I am aware of these problems locally
>> because there are a great many drivers who will not pass a bicyclist
>> climbing a grade on a curvy road even if the bicyclists rides outside
>> of the edge stripe on a paves highway.  On an unpaved road this could
>> case traffic jams even with light auto traffic.

> You're right about contention for space.  Actual traffic jams should
> be addressed.  But drivers who are just pissy because they can't put
> the pedal to the metal should not be pandered to like big babies, at
> the expense of other road users.  Unfortunately most managers would
> not want to face the issue, and would prefer it never arise.  Thus
> the ban.

They are only looking out for your safety... so goes the word.  It's
hard to argue with that.  You may not have noticed, but the people
backed up behind one of these bike watchers are pissed off at the
bicyclist, not the car driver.

http://draco.acs.uci.edu/rbfaq/FAQ/6.1.html

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Rim brake heat and clincher blowoff, was Re: Potential good news 
	for Mt. Washington access.
Newsgroups: rec.bicycles.misc
Message-ID: <Di0Ed.812$m31.10093@typhoon.sonic.net>
Date: Sun, 09 Jan 2005 02:04:19 GMT

Matt O'Toole writes:

>> This isn't about MTB's.  It is primarily a road bicycle problem.
>> It takes the same pressure to blow a skinny tire off a rim as a fat
>> one, the interface being the inside width of the rim, on which
>> inflation pressure acts (between tire and rim).  If your 2.5" MTB
>> tire on a narrow rim can withstand 140psi then you may be able to
>> experience blow-off.  On the other hand, starting at 45psi, I doubt
>> that you could get enough pressure even if you have a wider rim.

> So perhaps a 25mm or 28mm tire at 90psi is safer than a 23mm one at
> 120psi?  Care to make an educated guess at what the threshold of
> safety is?  Wouldn't it be interesting to test this?

Interesting that you mention that, because I am working on a test for
blow-off.  I made a valve stem pressure sensor adapter that, when
installed, opens the Presta valve to an aneroid pressure sensor that
sends its readings to a data-logger (about the size of a deck of
cards) that also reads a thermocouple attached to the rim.  The data
logger is tied to the inside of the wheel near the hub and has a USB
connector to download test data to a PC where it can be charted.

The plan is to descend Hicks Road near Los Gatos CA using only the
rear brake at about 15mph until the tire blows off.  Since this is
essentially a straight run, there is no problem stopping with a flat
rear tire.  Each such run will require a new tube and I think the
second run should make clear whether this is reasonably repeatable.
Of course I'll have to cool the rim down with water before running
again and pump the tire to the same pressure.

I will also test a 1950's French touring rim tape that was designed to
prevent tire blow-off but was never recognized as such, and was
therefore, unmarketable from the Cupertino Bike Shop of those days.
After having not ridden down Hicks Rd.  since the days of my insulated
tubulars, I was concerned about this descent the last few times I
recently came down that hill and recall reading about a fatality in
2004 on that road... attributed to lack of rider skill.

Not to worry, the results will be announced.  There is still a matter
of designing a small circuit board for the thermocouple.  I hope to
see a product emerge from this.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Rim brake heat and clincher blowoff, was Re: Potential good news 
	for Mt. Washington access.
Newsgroups: rec.bicycles.tech
Message-ID: <VkiEd.951$m31.11857@typhoon.sonic.net>
Date: Sun, 09 Jan 2005 22:35:33 GMT

Tom Compton writes:

>> Interesting that you mention that, because I am working on a test
>> for blow-off.  I made a valve stem pressure sensor adapter that,
>> when installed, opens the Presta valve to an aneroid pressure
>> sensor that sends its readings to a data-logger (about the size of
>> a deck of cards) that also reads a thermocouple attached to the
>> rim.  The data logger is tied to the inside of the wheel near the
>> hub and has a USB connector to download test data to a PC where it
>> can be charted.

> I have a model of rim heating caused by descending.  I would be
> interested in seeing your data to see how well the model predicts
> the temperature.

As I have related a few times, I have experience with rim heating, in
the days of riding tubulars, riding clinchers, riding in the Alps on
extremely steep roads, roads that required cooling down stops, and
blowing off tires on some descents.  I also have done accident
reconstruction in law suits claiming that a crash occurred from bicycle
shop wheel building malpractice where blow-offs were the cause.  Of
course this can be shown because the rim was sliding on the road
leading to the crash.  The wheel collapsed as a result of the crash
rather than being the cause.

My interest lies in the rate of pressure rise and the effect of
insulating rim strips.  If the effect of an insulator is good enough,
we can be done with much of the problem.  Rims heat up in a few yards
of braking but heat transfer to the air in the tube takes longer or we
would see blow-offs regularly.  One hard downhill stop from 30mph is
enough to heat a rim to peak temperatures and we do that all the time
on roads like the Grossglockner and Stelvio passes in the Alps or even
Sonora Pass in the Sierra Nevada.  What we don't do is maintain these
temperatures for long enough to raise inflation pressures to the
critical level.

My experience with water in the rim producing steam at each hairpin
turn and immediately cooling off as the brakes were released makes
clear how greatly air cooling affects rim temperature.  The hissing
sound of the tire apparently going flat ceased each time, a few
seconds after releasing the brakes.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Rim brake heat and clincher blowoff, was Re: Potential good news 
	for Mt. Washington access.
Newsgroups: rec.bicycles.tech
Message-ID: <mVmEd.988$m31.12273@typhoon.sonic.net>
Date: Mon, 10 Jan 2005 03:47:30 GMT

Terry Morse writes:

>> My experience with water in the rim producing steam at each hairpin
>> turn and immediately cooling off as the brakes were released makes
>> clear how greatly air cooling affects rim temperature.  The hissing
>> sound of the tire apparently going flat ceased each time, a few
>> seconds after releasing the brakes.

> That experience doesn't tell you much about the cooling rate, since
> boiling water stops boiling almost immediately after removal of the
> heat source.  You can see this effect when removing a boiling pot of
> water from a stove.

I think that is not the right model.  The rim was not full of water
but merely had a few cc's.  If there was much heat in the rim the tiny
amount of steam generation would not have cooled it so fast.  What
you suggest would mean that a fog spray from a Windex bottle would cool
rims sufficiently to prevent overheating.  From my experience with
descending in rain, that doesn't do the trick.

http://www.windexglasscleaner.com/

Rather than saying my assessment is wrong, can you suggest a better
scenario of rim heating.  As I pointed out, steam generation occurred
after only a few meters of hard braking.  How much heat do you think
is generated and what does this do for tandem riders?

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Rim brake heat and clincher blowoff, was Re: Potential good news 
	for Mt. Washington access.
Newsgroups: rec.bicycles.tech
Message-ID: <p8zEd.1091$m31.12944@typhoon.sonic.net>
Date: Mon, 10 Jan 2005 17:42:45 GMT

Paul Kopit writes:

>> Not to worry, the results will be announced.  There is still a
>> matter of designing a small circuit board for the thermocouple.  I
>> hope to see a product emerge from this.

> Try 2 different tube of different weights and/or thickness.  A
> skinny one that is stretched when inflated and a roomier one that
> needs to be shoved into the tire.

I'm looking for a trend here, realizing that different rim tape,
thickness of tube, thickness if tire casing (for cooling), type of
rim, quality of tire bead and a slew of other effects play a role.  I
have two goals.  To show that tires blow off from increased inflation
pressure through brake heating; a concept that has been challenged
here often, and that an insulating rim tape can reduce that effect
substantially.  Ultimately, I would like to see rim tapes for road
riding in mountains to be a standard product once more.  As I said,
I have such rim tapes from the 1950's.

> From my experience on the tandem, I think that the tubes blow from
> the heat of the rim.  Thermoplastic rim tape also is a disaster.

Please explain that last concept.  Are you saying the tube fails
without the tire coming off the rim?  How does a plastic rim tape
affect this?

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Rim brake heat and clincher blowoff, was Re: Potential good news 
	for Mt. Washington access.
Newsgroups: rec.bicycles.tech
Message-ID: <Q4EEd.1282$m31.13488@typhoon.sonic.net>
Date: Mon, 10 Jan 2005 23:20:16 GMT

Matt O'Toole writes:

>> To show that tires blow off from increased inflation pressure
>> through brake heating; a concept that has been challenged here
>> often, and that an insulating rim tape can reduce that effect
>> substantially.  Ultimately, I would like to see rim tapes for road
>> riding in mountains to be a standard product once more.  As I said,
>> I have such rim tapes from the 1950's.

> Do you mean a rim tape designed with insulation in mind?  Or were
> older rim tapes better insulating by accident?

These insulating rim tapes were available at the time when we were all
riding tubulars and when we switched to clinchers, no one recalled
these insulators, or for that matter, recognized that they were
insulators.  These rim strips are loose bias weave cotton 'hoses'
about 10mm in diameter, filled with kapok having a short flat piece of
rubberized cloth with at the stem hole.  They do not interfere with
the tire mounting because they can be compressed laterally and then
conform to the bed of the rim between the beads of the tire on
inflation.

I recall that they, as the Clement hard glue for tubulars, were a
mystery to riders of that era.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Rim brake heat and clincher blowoff, was Re: Potential good news 
	for Mt. Washington access.
Newsgroups: rec.bicycles.tech
Message-ID: <abEEd.1284$m31.13365@typhoon.sonic.net>
Date: Mon, 10 Jan 2005 23:27:02 GMT

Paul Kopit writes:

>> Please explain that last concept.  Are you saying the tube fails
>> without the tire coming off the rim?  How does a plastic rim tape
>> affect this?

> I believe that the tube fails due to the heat and not the pressure
> and ruptures.  That forces the bead off the rim.

Oh!  Then how do you explain the loud bang when the tire goes flat?
Have you seen any melting or similar deformation on such a tube?

http://www.sheldonbrown.com/brandt/blowouts.html

> Plastic rim tape melts and that forces the tube into the nipple socket
> or puts the tube more directly in contact with the hot rim.

Oh BS!  I've been riding Kool-Stop plastic rim strips for many years
and have not had any problems, hot as my rims have gotten.  I now have
one Rolf plastic/mesh rim strip that also works fine.  Pleas explain
on what you base this finding.

Jobst Brandt
jobst.brandt@stanfordalumni.org