Re: Is my tire bad? - Page 3

Jim Smith wrote:
> NiteRider <stingray@bowlander.bike> writes:
>
>> In article <c5fg411mjpscmi0dsa7nj8e81iptosrgdc@4ax.com>, Neil Brooks
>> <Neil0502@yahoo.com> wrote:
>>
>>> Jim Smith <3.141592six@gmail.com> wrote:
>>>>> You can "believe" whatever you want. I know what happened.
>>>>
>>>> It is refreshing to hear from someone who doesn't get bogged down
>>>> in technical details. I especialy enjoy seeing more faith-based
>>>> "thinking" applied to bicycles.
>>
>> Fine, Mr. Wizard. If you're so technically inclined, please tell me
>> the composition and yield strength of the alloy my rim was made
>> with, the point loads applied by a crooked bead on a rim edge, point
>> out any and all stress risers and calculate the strain on the rim's
>> flange. Can't do it? Didn't think so. Tell me, just what engineering
>> degree do you have? Or are you just relying on "faith" that you've
>> accumulated from years of bicycling?
>
> Not that it matters, but I have a sciency job and I consider myself a
> scientician. I do have an undergraduate degree in engineering from
> Berkeley (I considered Stanford, but decided I should go to a good
> school.) True, I did major in electrical engineering, but I did take
> statics, dynamics, strength of materials, and some continuum
> mechanics (hooray for tensor calculus!)
>
> You are right, I don't know what sort of alloy your rims are made of,
> but I bet their yeild strength is somewhere between 50 and 300 mega
> pascals. Other than that, I don't care to play your silly game. I
> would much rather tell you how smart I am.
>
> Anyhoo, how are things at the community college working out for you?
> You ever going to finish that bachelor of pseudoscience in trance
> channeling?
>
> HTH HAND

The only thing worse than a bully is a smart bully.

Bill S., B.A., Basket Weaving '77

The pressure on a rim, when it is inflated is constant, that is to say,
there is not more pressure on one part of the rim than another. What
the many writers of this group are pointing out is that, at a constant
pressure there is no way to cause an irregularity of that type with a
tire pumped to any pressure. The force required to deform the rim in
that manner had to be greater in that single spot than any other on the
rim. Additionally you can notice the rim has a fairly severe apex to
which it was bent. This fact also disallows tire pressure as being the
culprit for this anomaly.

Josh McClure
Durst Cycles

carlfogel@comcast.net wrote:
> On Mon, 28 Mar 2005 19:51:36 GMT, NiteRider
> <stingray@bowlander.bike> wrote:
>
>
>>In article <c6ig41d8kkngphf4omilfs81vttr9bjkf9@4ax.com>,
>><carlfogel@comcast.net> wrote:
>>
>>
>>>On Mon, 28 Mar 2005 16:57:47 GMT, NiteRider
>>><stingray@bowlander.bike> wrote:
>>>
>>>
>>>>In article <114f5q4kuu4caa3@corp.supernews.com>, A Muzi
>>>><am@yellowjersey.org> wrote:
>>>>
>>>>
>>>>>I do not believe that you can damage a rim by inflation
>>>>>pressure of 80psi no matter how poorly mounted.
>>>>
>>>>You can "believe" whatever you want. I know what happened.
>>>
>>>Dear NiteRider,
>>>
>>>Andrew's point is simply that any non-defective bicycle
>>>wheel rim can easily restrain a tire inflated to 80 psi. No
>>>matter how the tire is mounted, the maximum pressure remains
>>>80 psi. A normal rim doesn't fail with excessive
>>>inflation--the tire just creeps over the edge, the inner
>>>tube goes bang! when exposed.
>>>
>>>He probably bases his opinion on common sense and over
>>>thirty years of inflating bicycle tires on every imaginable
>>>kind of rim at a high-volume bicycle shop.
>>>
>>>If your rim failed when the tire was inflated to that
>>>pressure, then it was a defective rim, either from the
>>>factory or else due to road damage or even brake pad wear.
>>
>>That's not what he wrote. He didn't differentiate between defective and
>>non-defective rims. He simply wrote that it's not possible. Period.
>>It's so easy to be a critic and a skeptic when you don't have something
>>happen to you personally. I accept that such a failure is possible. The
>>skeptics simply wave their hands and say it's impossible. Who is the
>>one with a closed mind here? People like this laughed at the Wright
>>brothers, because their "years of experience" told them
>>heavier-than-air flight was impossible. Not that I'm comparing myself
>>with the Wrights, but it's the same kind of mentality they encountered.
>>
>>The fact is that it happened at home. That's no lie. The fact is that
>>there are two such dents roughly 12 inches apart. No road damage could
>>account for two dents. The fact is that that wheel has a hub brake and
>>is not subject to brake wear. Instead of accepting these facts and
>>trying to figure out what really happened, all I seem to hear around
>>here is "not possible. You're a troll, a liar. You don't have any idea
>>what you're talking about." Sure, there's the occasional reasonable
>>person who says the rim may have been defective, like yourself. But
>>nobody likes being called a liar.
>
>
> Dear NiteRider,
>
> I agree that some posts have treated you to the usual
> obnoxious responses common on this newsgroup. But Andrew
> really wasn't behaving that way--you've just had to put up
> with such rudeness that you're easilly upset.
>
> For example, I should have re-read the whole thread and seen
> that you've mentioned that the hub brake eliminates pad wear
> as a culprit. So I was rude, but not intentionally.
>
> But we're all prone to such slips. I don't think that you're
> trying to be rude when you say that no road damage could
> account for two dents--but I do think that you should
> reconsider that notion. Why can't a wheel hit two things if
> it hits one?
>
> Most riders would have trouble telling if they hit one bump
> or two bumps a foot apart at higher speeds. At 20 mph, the
> wheel is rolling about 30 feet per second, so banging over a
> pair of nasty inch-high rocks a foot apart would take only a
> thirtieth of a second--and we can't tell that camera film is
> showing still pictures 1/24th of a second apart.
>
> And the odds are fair that a rider might hit the same damned
> bump coming and going--which in turn gives good odds that a
> different section of the wheel would hit the bump coming
> home.
>
> Consider also that the failure is on the rear wheel, which
> is the more heavily loaded wheel and far more prone to road
> damage. The front wheel is not only less heavily loaded, but
> also enjoys a much more flexible frame arrangement than the
> rear diamond.
>
> (You've indicated that you don't think that there was any
> impact, much less two, but anyone like Andrew Muzi is
> painfully aware that customers bring bikes in with obvious
> road damage and sincerely believe it couldn't have happened.
> They're not lying--they just can't believe that the dents
> and cracks came from impacts that they didn't notice or
> don't remember. I learned long ago that my clients aren't
> lying when they insist that they didn't do such and so on
> their computers--if they'd realized that they were doing it,
> they wouldn't have done it in the first place.)
>
> While no one would mistake me for an engineer, it does
> strike me that two short sections of a rim bulging out
> doesn't seem like excessive tire pressure on a non-defective
> rim. If you get a tire strong enough to withstand pressures
> that will damage a non-defective rim and pump it up higher
> and higher, a much larger section of the rim should bend
> outward. A pair of small, localized failures suggests either
> some irregular defect in the manufacturing process, two
> places where road damaged occurred, or a combination.
>
> If a mis-mounted tire somehow crept and applied significant
> extra pressure on one small section, there would be only one
> local failure--the shape of the tire and a non-defective rim
> would prevent the tire from creeping out elsewhere to cause
> a second failure.
>
> If pumping up the tire to 80 psi causes dents and bulges to
> form in the rim, then the rim is extraordinarily defective.
> A much more likely explanation is that there were already
> dents and bulges, pumping the tire up added pressure to the
> already defective rim and bent things even more, and then
> the tire slipped off, with the usual inner-tube explosion.
>
> As Andrew pointed out, 80 psi doesn't bend normal bicycle
> rims. He could have added all the qualifiers and exceptions
> that I'm adding, but he has more common sense than I do and
> less time for beating the obvious to death.
>
> I hope your new rim lasts longer.
>
> Carl Fogel

for a good quality rim in good condition, it is indeed most unlikely
that a tire can be pumped sufficiently to bend the rim before blow-off,
but that doesn't mean it can't happen - there has to be some pressure at
which it occurs. once that principle is established, it's then a matter
of quantification.

now, on the pics you're hosting,
http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
the third frame shows clearly that the rim has cracked. this results in
material compromise to the integrity of the rim, and as mentioned
previously regarding fatigue & stress orientation perpendicular to the
extrusion axis, excess pressure is definitely going to play a
significant role in crack formation & propagation. if cracking is
present with our subject, then it absolutely /is/ possible for
niterider's rim to bulge where cracked, at the pressures mentioned, and
there's no reason why it can't happen in two places at once. fatigue
/does/ occur below yield and /does/ result in failures at stresses below
what might be considered "normal service".

jim beam wrote:

> for a good quality rim in good condition, it is indeed most unlikely
> that a tire can be pumped sufficiently to bend the rim before
blow-off,
> but that doesn't mean it can't happen - there has to be some pressure
at
> which it occurs. once that principle is established, it's then a
matter
> of quantification.

If the 2 spots on the rim were folded down by the force of the tire
bead after the bead lifted off but before the tube blew, I would think
either the rim would have to be extremely fragile (and ductile) and/or
the pressure very high. I wonder if the tire was being filled from a
high pressure source (compressor)? It could theoretically be possible
to get very high pressures (>200 psi) before liftoff.

On 29 Mar 2005 14:32:06 -0800, "Peter Cole"
<peter_cole@comcast.net> wrote:

>
>jim beam wrote:
>
>> for a good quality rim in good condition, it is indeed most unlikely
>> that a tire can be pumped sufficiently to bend the rim before
>blow-off,
>> but that doesn't mean it can't happen - there has to be some pressure
>at
>> which it occurs. once that principle is established, it's then a
>matter
>> of quantification.
>
>If the 2 spots on the rim were folded down by the force of the tire
>bead after the bead lifted off but before the tube blew, I would think
>either the rim would have to be extremely fragile (and ductile) and/or
>the pressure very high. I wonder if the tire was being filled from a
>high pressure source (compressor)? It could theoretically be possible
>to get very high pressures (>200 psi) before liftoff.

Dear Pete,

I think that NiteRider was just pumping it up by hand and
mentioned pressures around 80 psi. Curiously, he requested
that Google not archive his posts, so they've been
disappearing. This is the closest that I could find to a
description:

"That time, I wasn't out on the road. I was in my apartment
having just finished mounting a brand new wire bead Metro on
the wheel. The wheel wasn't even back on my bike. Pumping it
up, it blew at around 50-60psi, surprisingly low in my
opinion but not inconsistent with a badly seated bead.
Pretty deafening in a confined space, too."

"It blew off again months later on the rim I rebuilt the
wheel with, a Campagnolo Thorr. But this second time was on
a ride and there was no apparent damage to that rim. That
the tire blew off two different rims is my source of
concern."

Here he mentions just 50-60 psi, but he may even have been
talking about something else--it's a bit confusing.

Here's another quote:

"Last season, I managed to have two major problems with one
tire, an IRC Metro/K. The first time was my fault.
apparently hadn't seated the new tire properly on the rim
and when I was pumping up, a few inches of bead came off and
the tube blew into pieces, bending the rim sidewall."

He's shaken the dust of this newsgroup from his cleats, but
picking through the quoted text in still-available posts
suggests that he pumps tires up by hand in an apartment and
that occasionally they explode, both in the room and on the
road, whereupon he notices rim damage. He felt that the tire
under pressure bent the rim out of shape, while everyone
else suggested that the rim was dented or damaged first,
weakening it enough to bend and allow the tire to creep off,
or that the rim was impressively defective from the factory.

Carl Fogel

Peter Cole writes:

>> for a good quality rim in good condition, it is indeed most
>> unlikely that a tire can be pumped sufficiently to bend the rim
>> before blow-off, but that doesn't mean it can't happen - there has
>> to be some pressure at which it occurs. once that principle is
>> established, it's then a matter of quantification.

> If the 2 spots on the rim were folded down by the force of the tire
> bead after the bead lifted off but before the tube blew, I would
> think either the rim would have to be extremely fragile (and
> ductile) and/or the pressure very high. I wonder if the tire was
> being filled from a high pressure source (compressor)? It could
> theoretically be possible to get very high pressures (>200 psi)
> before liftoff.

This is not a reasonable pursuit. The rim would not bend at the place
where the tire first lifted off because that is a region of reduced
stress, the tire bead no longer having a hold on the rim. I don't see
why, in face of many years of experience by professional bicycle
people, this scenario is given so much consideration. This is all
based on a report from someone who believes this is what occurred and
who asks, whether the scenario is probable.

It isn't.

Jobst.Brandt@stanfordalumni.org

Jim Smith wrote:

> ...I do have an undergraduate degree in engineering from
> Berkeley (I considered Stanford, but decided I should go to a good
> school.)...

Are there any Stanford alumni on rec.bicycles.tech who might be offended?

--
Tom Sherman - Earth (Downstate Illinois, North of Forgottonia)

Carl Fogel wrote:

> ...
> (You've indicated that you don't think that there was any
> impact, much less two, but anyone like Andrew Muzi is
> painfully aware that customers bring bikes in with obvious
> road damage and sincerely believe it couldn't have happened.
> They're not lying--they just can't believe that the dents
> and cracks came from impacts that they didn't notice or
> don't remember. I learned long ago that my clients aren't
> lying when they insist that they didn't do such and so on
> their computers--if they'd realized that they were doing it,
> they wouldn't have done it in the first place.)...

Carl Fogel is a self-appointed expert at detecting when people are lying.

--
Tom Sherman - Earth (Downstate Illinois, North of Forgottonia)

Tom Sherman <tsherman@qconline.com> writes:

> Jim Smith wrote:
>
>> ...I do have an undergraduate degree in engineering from
>> Berkeley (I considered Stanford, but decided I should go to a good
>> school.)...
>
> Are there any Stanford alumni on rec.bicycles.tech who might be offended?

I don't see how anyone could take offense. Berkeley's superiority to
Stanford is a well established fact.

jobst.brandt@stanfordalumni.org wrote:
> Peter Cole writes:
>
>
>>>for a good quality rim in good condition, it is indeed most
>>>unlikely that a tire can be pumped sufficiently to bend the rim
>>>before blow-off, but that doesn't mean it can't happen - there has
>>>to be some pressure at which it occurs. once that principle is
>>>established, it's then a matter of quantification.
>
>
>>If the 2 spots on the rim were folded down by the force of the tire
>>bead after the bead lifted off but before the tube blew, I would
>>think either the rim would have to be extremely fragile (and
>>ductile) and/or the pressure very high. I wonder if the tire was
>>being filled from a high pressure source (compressor)? It could
>>theoretically be possible to get very high pressures (>200 psi)
>>before liftoff.
>
>
> This is not a reasonable pursuit. The rim would not bend at the place
> where the tire first lifted off because that is a region of reduced
> stress, the tire bead no longer having a hold on the rim. I don't see
> why, in face of many years of experience by professional bicycle
> people, this scenario is given so much consideration. This is all
> based on a report from someone who believes this is what occurred and
> who asks, whether the scenario is probable.
>
> It isn't.
>
> Jobst.Brandt@stanfordalumni.org

did you or peter ever bother to look at the cracks in the 3rd panel of
this pic?

http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg

and have you two ever bothered to consider the effects of fatigue caused
by excess tire pressure, particularly with regard to the orientation of
the extrusion axis?

Southern Comfort writes:

>>>> for a good quality rim in good condition, it is indeed most
>>>> unlikely that a tire can be pumped sufficiently to bend the rim
>>>> before blow-off, but that doesn't mean it can't happen - there
>>>> has to be some pressure at which it occurs. once that principle
>>>> is established, it's then a matter of quantification.

>>> If the 2 spots on the rim were folded down by the force of the
>>> tire bead after the bead lifted off but before the tube blew, I
>>> would think either the rim would have to be extremely fragile (and
>>> ductile) and/or the pressure very high. I wonder if the tire was
>>> being filled from a high pressure source (compressor)? It could
>>> theoretically be possible to get very high pressures (>200 psi)
>>> before liftoff.

>> This is not a reasonable pursuit. The rim would not bend at the
>> place where the tire first lifted off because that is a region of
>> reduced stress, the tire bead no longer having a hold on the rim.
>> I don't see why, in face of many years of experience by
>> professional bicycle people, this scenario is given so much
>> consideration. This is all based on a report from someone who
>> believes this is what occurred and who asks, whether the scenario
>> is probable. It isn't. Jobst.Brandt@stanfordalumni.org

> Did you or peter ever bother to look at the cracks in the 3rd panel
> of this pic?

http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg

You must think everyone is blind but you. Of course the crack was
apparent. So what?

> And have you two ever bothered to consider the effects of fatigue
> caused by excess tire pressure, particularly with regard to the
> orientation of the extrusion axis?

It may not have occurred to you that cracks and failure can be caused
by forced rupture and that the bend in the rim material shows that the
crack came after the bend that wouldn't be smooth but rather a kink at
the weak spot where the crack now is, had it been there as a cause.

Jobst.Brandt@stanfordalumni.org

On Tue, 29 Mar 2005 19:49:46 -0800, jim beam
<nospam@example.net> wrote:

>jobst.brandt@stanfordalumni.org wrote:
>> Peter Cole writes:
>>
>>
>>>>for a good quality rim in good condition, it is indeed most
>>>>unlikely that a tire can be pumped sufficiently to bend the rim
>>>>before blow-off, but that doesn't mean it can't happen - there has
>>>>to be some pressure at which it occurs. once that principle is
>>>>established, it's then a matter of quantification.
>>
>>
>>>If the 2 spots on the rim were folded down by the force of the tire
>>>bead after the bead lifted off but before the tube blew, I would
>>>think either the rim would have to be extremely fragile (and
>>>ductile) and/or the pressure very high. I wonder if the tire was
>>>being filled from a high pressure source (compressor)? It could
>>>theoretically be possible to get very high pressures (>200 psi)
>>>before liftoff.
>>
>>
>> This is not a reasonable pursuit. The rim would not bend at the place
>> where the tire first lifted off because that is a region of reduced
>> stress, the tire bead no longer having a hold on the rim. I don't see
>> why, in face of many years of experience by professional bicycle
>> people, this scenario is given so much consideration. This is all
>> based on a report from someone who believes this is what occurred and
>> who asks, whether the scenario is probable.
>>
>> It isn't.
>>
>> Jobst.Brandt@stanfordalumni.org
>
>did you or peter ever bother to look at the cracks in the 3rd panel of
>this pic?
>
>http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>
>and have you two ever bothered to consider the effects of fatigue caused
>by excess tire pressure, particularly with regard to the orientation of
>the extrusion axis?

Dear Jim,

Hmmm . . . now that I look at the pictures again, it strikes
me that the rim seems to be damaged severely on only one
side, so maybe my faith in the rim hitting something is too
childlike and trusting.

So now I hope that everyone will tell me interesting tales
about whether rims that narrow often sustain such heavy
damage on only one side.

As for the fatigue idea, I'm still puzzled and probably
breathtakingly ignorant.

Is the sideways pressure on the rim steady, or does it
increase when it rolls under the hub?

Is the pressure greater at the edge or down in the well?

Would the crack come first, leading to the outward bend, or
would the bend come first, followed by the crack?

Carl Fogel

On Wed, 30 Mar 2005 04:28:32 GMT,
jobst.brandt@stanfordalumni.org wrote:

>Southern Comfort writes:
>
>>>>> for a good quality rim in good condition, it is indeed most
>>>>> unlikely that a tire can be pumped sufficiently to bend the rim
>>>>> before blow-off, but that doesn't mean it can't happen - there
>>>>> has to be some pressure at which it occurs. once that principle
>>>>> is established, it's then a matter of quantification.
>
>>>> If the 2 spots on the rim were folded down by the force of the
>>>> tire bead after the bead lifted off but before the tube blew, I
>>>> would think either the rim would have to be extremely fragile (and
>>>> ductile) and/or the pressure very high. I wonder if the tire was
>>>> being filled from a high pressure source (compressor)? It could
>>>> theoretically be possible to get very high pressures (>200 psi)
>>>> before liftoff.
>
>>> This is not a reasonable pursuit. The rim would not bend at the
>>> place where the tire first lifted off because that is a region of
>>> reduced stress, the tire bead no longer having a hold on the rim.
>>> I don't see why, in face of many years of experience by
>>> professional bicycle people, this scenario is given so much
>>> consideration. This is all based on a report from someone who
>>> believes this is what occurred and who asks, whether the scenario
>>> is probable. It isn't. Jobst.Brandt@stanfordalumni.org
>
>> Did you or peter ever bother to look at the cracks in the 3rd panel
>> of this pic?
>
> http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>
>You must think everyone is blind but you. Of course the crack was
>apparent. So what?
>
>> And have you two ever bothered to consider the effects of fatigue
>> caused by excess tire pressure, particularly with regard to the
>> orientation of the extrusion axis?
>
>It may not have occurred to you that cracks and failure can be caused
>by forced rupture and that the bend in the rim material shows that the
>crack came after the bend that wouldn't be smooth but rather a kink at
>the weak spot where the crack now is, had it been there as a cause.
>
>Jobst.Brandt@stanfordalumni.org

Dear Jobst,

If I'm following you, you're saying that the rim was first
forced to bend out by something, causing the crack to appear
as a forced rupture, not a slowly growing fatigue crack.

http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg

But I'm not sure what you're saying would have kinked, where
it would have kinked, or which way it would have kinked if
it had been a fatigue crack leading to the bend.

This rim failed after heavy brake pad wear:

http://home.comcast.net/~carlfogel/download/rim.jpg
http://home.comcast.net/~carlfogel/d.../rimdetail.jpg

Dumb questions.

Is that a forced rupture of the kind that you have in mind
after heavy wear rather than fatigue?

And is the split in the middle of the dangling strip the
result of the kind of kink that you have in mind?

I'm really just asking for elaboration or even kinky
pictures, which I'd be glad to host. I'm not sure what the
differences would be between a rim bent out and ruptured and
a rim fatigued.

Carl Fogel

Carl Fogel writes:

> If I'm following you, you're saying that the rim was first forced to
> bend out by something, causing the crack to appear as a forced
> rupture, not a slowly growing fatigue crack.

http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg

That is correct, and as I mentioned, if the crack were there first,
the bend would be abrupt at that line and the edge of the rim would not
have the classic curl, caused by running over a one inch rock, for
instance.

> But I'm not sure what you're saying would have kinked, where it
> would have kinked, or which way it would have kinked if it had been
> a fatigue crack leading to the bend.

It would have a sharp bend there because it was broken. As it is the
root of the curled rim sidewall was solid and strong enough to make
the rim curl at the top edge first and finally cause a crack where the
bend could not continue, there being a transverse member.

> This rim failed after heavy brake pad wear:

http://home.comcast.net/~carlfogel/download/rim.jpg
http://home.comcast.net/~carlfogel/d.../rimdetail.jpg

> Is that a forced rupture of the kind that you have in mind after
> heavy wear rather than fatigue?

No, but the failure you see here occurred to a rim that had been worn
far thinner than the one above and you see what it did. Although it
was far weaker, it failed at the base of the sidewall with no curl to
the top.

> And is the split in the middle of the dangling strip the result of
> the kind of kink that you have in mind?

Well it isn't the type of failure attributed to an otherwise healthy
rim. It is what one expects of a cracked or worn-thin sidewall. If
you've seen a few of these as the bicycle shop guys on this newsgroup
have, there is no doubt about the cause.

> I'm really just asking for elaboration or even kinky pictures, which
> I'd be glad to host. I'm not sure what the differences would be
> between a rim bent out and ruptured and a rim fatigued.

A fatigued rim wold have no deformation, only a long crack and
separation of the sidewall from the base of the rim. That's the whole
concept of fatigue failure. It separates on a crack line without
other deformation because it operated below yield. The rim with the
dent in it had a heavy blow that caused it to yield locally.

Jobst.Brandt@stanfordalumni.org

jim beam wrote:
> jobst.brandt@stanfordalumni.org wrote:
> > Peter Cole writes:
> >
> >
> >>>for a good quality rim in good condition, it is indeed most
> >>>unlikely that a tire can be pumped sufficiently to bend the rim
> >>>before blow-off, but that doesn't mean it can't happen - there has
> >>>to be some pressure at which it occurs. once that principle is
> >>>established, it's then a matter of quantification.
> >
> >
> >>If the 2 spots on the rim were folded down by the force of the tire
> >>bead after the bead lifted off but before the tube blew, I would
> >>think either the rim would have to be extremely fragile (and
> >>ductile) and/or the pressure very high. I wonder if the tire was
> >>being filled from a high pressure source (compressor)? It could
> >>theoretically be possible to get very high pressures (>200 psi)
> >>before liftoff.
> >
> >
> > This is not a reasonable pursuit. The rim would not bend at the
place
> > where the tire first lifted off because that is a region of reduced
> > stress, the tire bead no longer having a hold on the rim. I don't
see
> > why, in face of many years of experience by professional bicycle
> > people, this scenario is given so much consideration. This is all
> > based on a report from someone who believes this is what occurred
and
> > who asks, whether the scenario is probable.
> >
> > It isn't.
> >
> > Jobst.Brandt@stanfordalumni.org
>
> did you or peter ever bother to look at the cracks in the 3rd panel
of
> this pic?
>
> http://home.comcast.net/~carlfogel/d...d/rim_nite.jpg
>
> and have you two ever bothered to consider the effects of fatigue
caused
> by excess tire pressure, particularly with regard to the orientation
of
> the extrusion axis?

Yes, I did, but I was struck by the curvature of the rim edge, I
wouldn't have thought that it would bend so far in a simple crack
failure. It was also surprising to hear that there were 2 such spots on
the rim, that seems a little too coincidental for fatigue failure. I'd
also find it difficult to believe that an experienced rider would dent
a rim that badly without remembering an impact (or 2), so I'm baffled.