Time for a Cookout -- we're having Crow

Quoted message said:

It's obvious to me that this failure was the result of overpressure in
the tire, pure and simple.

Oh my God there is absolutely no way that that could have happened! You
know nothing about bikes! I've worked in XXXXXX industry for [censored] years and
this has never happened to me so it can't happen to anyone else!

Quoted message said:

That caused the rim to crack in 2 spots
several inches apart, just as the hapless guy, who had his integrity
and intelligence questioned, claimed had happened to him.

You don't have your head on straight... not only that, you're dumb!

Quoted message said:

A scenario
that was declared by some to be impossible. Crow anyone?

Nope... never in a million years... couldn't have happened!!!
</sarcasm and big smiley>

This picture is a better picture than the other ones, since the depth is
more easily perceived than in the other ones. I don't see how this couldn't
have happened... all the factors point to tire blow-off, namely a
larger-volume tire, faulty gauge, a high-schooler,
hasty-prior-to-attending-school pumping, and a formidable pump with plenty
of capacity.

NiteRider's picture, however, shows a very short portion of rim that's bent
out. That's the big difference here. I think most of us are thinking that
the rim couldn't have blown out on such a small circumference.

In a similar thread, I have blown off the tire tread off of the bead of the
tire on a MTB. It was a Hutchinson Python Airlite on a Mavic X221 rim on a
brand new bike. The sidewall claims 80psi max, but the bead definitely
separated out of the tire. Hutchinson (and I) made a bad call setting 80psi
max on a 480-gram MTB tire. Note that this isn't a tire blowoff, this is a
tread/bead separation. The rim was fine, and is actually still in service.

I have some photos of a rim that was actually squarely hit on the rim,
bending it outwards like NiteRider's, but the tire never came off the rim
and the tube never blew out. I'll find it and post it soon.
--
Phil, Squid-in-Training

Peter, this is a common rim failure of Mavic MA-2 and Open 4CD rims. It is
caused NOT by overinflation but by a pressure pulse caused by hitting
something such as a stone or a pothole or such. The split rim is caused by
brake wear on the braking surface. If you look around the rim you'll
probably discover cracking or excessive wear in other sectors as well. And
if you look at the smaller failure you can see that it was caused by hitting
some sort of object. This is what caused the pressure pulse. But the rim was
on the edge of failure anyway and perhaps the real failure was caused by the
rim splitting from wear and the second damage was caused by your son trying
to save the bike and hitting something AFTER the failure.

If you look more closely at theoriginal photos you'll see that the rim is
not just bent outwards as an overpressure condition will cause, but is
rolled completely 180 degrees which can only be caused by hitting something
in the road.

Now, because the same act that bent the rim flatted the tire almost
instantly and since whatever caused it might have been a stone the same
color as the road and essentially invisible and may have been thrown off of
the road the victim might have no ability to detect that it was a stone save
from the perfectly clear interpretation of the damaged rim.

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

Quoted message said:

Well, maybe not all of us...

A few weeks ago, there was a heated exchange surrounding the experience
of a guy who claimed his rim bent from a tire coming unseated <Is my
tire bad?> :

Quoted message said:

Last season, I managed to have two major problems with one tire, an
IRC Metro/K. The first time was my fault. I 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.

Pictures were posted:
<http://home.comcast.net/~carlfogel/download/rim_nite.jpg>

Aspersions were cast, accusations were hurled, the fray centered on the
charge that the rim damage must have been caused by impact, something
the OP vehemently (that's putting it mildly as I recall) denied. The
claim was made that overinflation could not have caused this damage.

In an interesting coincidence, I was called this afternoon by my 16 YO
son to get a pickup because his rear wheel was trashed. Upon arrival,
examination of the wheel, and interrogation of my enthusiastic, but
naive-in-the-ways-of-wheels son, I determined that:

He inflated the tire this morning before setting off to school (one of
perhaps 8 in a student body of 2,000+ who rides). I asked him how high.
He replied he had no idea, since the "stupid pump gauge jumps all over
the place". An aside: we have the typical "Joe Blow" with a leaky
chuck, so typically the gauge overshoots until the presta unsticks,
then undershoots as the air leaks from the hose/chuck. The actual
correct pressure is just before the leaking, I've told him that, but if
you have, or have had, a 16 YO son, you'll understand. The upshot is
that the pressure in the tire may have been whatever an enthusiastic
and reasonably strong teenage boy could force from a good floor pump.

The rim was a Mavic "Reflex", with substantial mileage (I had retired
it from my front wheel last spring, but pressed it back into service
when his bike got vandalized). The tire was a Panaracer Pasela,
nominally 32 mm, but they run narrower. This somewhat beefy tire was a
(futile) attempt to reduce pinch flats, he had just had another a few
days ago, which precipitated my lecture to "pump the tires up well
before every ride". He did (too well, apparently), and after riding the
bike to school uneventfully this AM, returned in the PM to find this:

<http://home.comcast.net/~peter_cole/Rim.jpg>

It may not be obvious from the rather poor picture, but the rim has
failed (cracked) in 2 places, several inches apart. The less severe
failure spot looks very much like the rim failure that caused all the
ruckus last month. Both sections of the rim are folded over nearly
horizontal. The tube had a large slit blowout, as you might imagine.

It's obvious to me that this failure was the result of overpressure in
the tire, pure and simple. That caused the rim to crack in 2 spots
several inches apart, just as the hapless guy, who had his integrity
and intelligence questioned, claimed had happened to him. A scenario
that was declared by some to be impossible. Crow anyone?

Tom Kunich said:

Peter, this is a common rim failure of Mavic MA-2 and Open 4CD rims.

It is

Quoted message said:

caused NOT by overinflation but by a pressure pulse caused by hitting

Quoted message said:

something such as a stone or a pothole or such. The split rim is

caused by

Quoted message said:

brake wear on the braking surface. If you look around the rim you'll
probably discover cracking or excessive wear in other sectors as

well. And

Quoted message said:

if you look at the smaller failure you can see that it was caused by

hitting

Quoted message said:

some sort of object. This is what caused the pressure pulse. But the

rim was

Quoted message said:

on the edge of failure anyway and perhaps the real failure was caused

by the

Quoted message said:

rim splitting from wear and the second damage was caused by your son

trying

Quoted message said:

to save the bike and hitting something AFTER the failure.

No, this is impossible. The failures occurred when the bike was parked.
The rim failures were so severe the bike could not have been ridden
with either of them. Whether the rim was worn or not is beside the
point. Two sections of that rim failed simultaneously from
overpressure. That's it. That's what happened to the OP as well.

Quoted message said:

If you look more closely at theoriginal photos you'll see that the

rim is

Quoted message said:

not just bent outwards as an overpressure condition will cause, but

is

Quoted message said:

rolled completely 180 degrees which can only be caused by hitting

something

Quoted message said:

in the road.

The spots are bent more like 90 degrees, exactly what I see when I look
closely at my rim. The smaller of the failures on my rim looks nearly
identical to Niterider's. Both rims show faint (but complete) cracks
there.

Quoted message said:

Now, because the same act that bent the rim flatted the tire almost
instantly and since whatever caused it might have been a stone the

same

Quoted message said:

color as the road and essentially invisible and may have been thrown

off of

Quoted message said:

the road the victim might have no ability to detect that it was a

stone save

Quoted message said:

from the perfectly clear interpretation of the damaged rim.

This was the interpretation that caused so much ill feeling. I found it
implausible then, impossible now.

As someone would say, you're clutching at straws.

I think you're seeing a failure caused by a worn out rim giving away. I
don't have an explanation of why it occurred with no rider.

Compare it to "blowouts" caused by the tube being pinched between the rim
and tire. Why don't they fail instantly or the moment you hit a bump?

-Dion

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

Quoted message said:

Tom Kunich said:

Peter, this is a common rim failure of Mavic MA-2 and Open 4CD rims.

It is

Quoted message said:

caused NOT by overinflation but by a pressure pulse caused by hitting

Quoted message said:

something such as a stone or a pothole or such. The split rim is

caused by

Quoted message said:

brake wear on the braking surface. If you look around the rim you'll
probably discover cracking or excessive wear in other sectors as

well. And

Quoted message said:

if you look at the smaller failure you can see that it was caused by

hitting

Quoted message said:

some sort of object. This is what caused the pressure pulse. But the

rim was

Quoted message said:

on the edge of failure anyway and perhaps the real failure was caused

by the

Quoted message said:

rim splitting from wear and the second damage was caused by your son

trying

Quoted message said:

to save the bike and hitting something AFTER the failure.

No, this is impossible. The failures occurred when the bike was parked.
The rim failures were so severe the bike could not have been ridden
with either of them. Whether the rim was worn or not is beside the
point. Two sections of that rim failed simultaneously from
overpressure. That's it. That's what happened to the OP as well.

On 11 Apr 2005 15:13:32 -0700, "Peter Cole" <[email hidden]>

Quoted message said:

<http://home.comcast.net/~peter_cole/Rim.jpg>

It may not be obvious from the rather poor picture, but the rim has
failed (cracked) in 2 places, several inches apart. The less severe
failure spot looks very much like the rim failure that caused all the
ruckus last month. Both sections of the rim are folded over nearly
horizontal. The tube had a large slit blowout, as you might imagine.

It's obvious to me that this failure was the result of overpressure in
the tire, pure and simple. That caused the rim to crack in 2 spots
several inches apart, just as the hapless guy, who had his integrity
and intelligence questioned, claimed had happened to him. A scenario
that was declared by some to be impossible. Crow anyone?

Because the failure became complete when the bike was at rest, I'll
agree that the rim's destruction took place when sufficient pressure
was applied to cause the existing weak points to give way. As
suggested by another poster, I suspect that a close examination of the
rim will reveal that the rim wall has wear and possibly scoring on the
outside from normal brake usage, and very close examination may find
more small fractures along either flange. (I will not rule out the
possibility that there may be an extrusion groove on the inside of the
flange at the point of failure, either, until somebody checks for
that.) Further, it appears that the shearing took place along a
shoulder where the radius was possibly a bit small and the wall was
already as thin as they were willing to make it. Without knowing how
much pressure was involved, I am unwilling to blame overpressure
*alone*, and I really doubt that the amount applied could have been
enough to have caused a failure had the rim been sound. You had
retired this rim, in my opinion, at the proper time and for good
reason. Returning it to service may have seemed safe, but like many
judgements examined in retrospect, this one doesn't look as good now.
It's *much* easier to be right when you're doing an autopsy than a
prediction, of course; I might well have done the same thing you did
under the circumstances, with identical results.

My call: If the rim was possible to destroy with the overpressure
that could have been generated by a hand pump, it was either worn out
or defective. If it was worn out, then it would have failed in
service at some point anyway. Be glad that it did so when the bike
was parked.

That's just my two cents' worth.

I stayed on the sidelines during the previous shouting match because
the failure, the reported circumstances, and the pictures added up to
something that had an aroma of seafood, and I couldn't figure out
where. The OPs comments from that thread left it clear that the rim
had been inspected sufficiently that such an obvious deformation in
the flange would have been detected prior to airing up the tire, so I
took the poster's statement that the flange deformed when the tire
unseated and blew out as being correct for lack of any other
explanation. This left me with the uneasy feeling that either the rim
in question must have been much too fragile, or it had a previously
undetected flaw at the failure location which was revealed when the
new tire was aired up. Close examination of the right-hand photo
shows a crack at the root of the flange in the center of the deformed
area, which, if it was present when the tire was aired up, might have
been the root of the failure...or might have been made when the flange
was rolled outward forcibly. I couldn't see a mechanism by which the
latter would have taken place, so I decided to stay out of the
discussion due to a lack of anything worthwhile to say. (This is, of
course, wildly out of character for me, but hey, every once in a while
I have to do it.)

In the case of your rim, however, the failure fits the pattern
observed in some other instances; a presumably worn rim, subjected to
enough pressure to shear the flange off, failed. As rims wear, the
pressure at which this can occur is gradually reduced. When the rim
wears enough for the failure point to be within the range of the
pressures generated by the compressor or pump, it fails, though
usually not right at the exact moment that the pressure is applied.
More often, the split happens several miles down the road, or even
hours later...but it's still a wear-related failure.

For my part, the crows can stay in the trees. I didn't read much of
the other thread and took no position there.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Peter Cole said:

No, this is impossible. The failures occurred when the bike was
parked. The rim failures were so severe the bike could not have
been ridden with either of them. Whether the rim was worn or not is
beside the point. Two sections of that rim failed simultaneously
from overpressure. That's it. That's what happened to the OP as
well.

Now that you mention it. The ding in the rim to the right looks
almost exactly like the one Nitrider posted. In any case, if this
occurred while parked and no one present then it was most likely break
wear that weakened the sidewall of the rim enough for it to slit. The
ding on the right part of the picture was not caused by tire pressure
as most of the folks who commented on Nitrider's claims said. A
curled ding bent 90 degrees to the side was caused by an impact.

Quoted message said:

Quoted message said:

Now, because the same act that bent the rim flatted the tire almost
instantly and since whatever caused it might have been a stone the
same color as the road and essentially invisible and may have been
thrown off of the road the victim might have no ability to detect
that it was a stone save from the perfectly clear interpretation of
the damaged rim.

Quoted message said:

This was the interpretation that caused so much ill feeling. I
found it implausible then, impossible now.

Quoted message said:

As someone would say, you're clutching at straws.

If you are sure about this then you must have an explanation for how a
local 90 degree bend in a rim can occur. The split on the left side
of the picture is consistent with experience others have had and rims
that I have seen.

[email hidden]

Tom Kunich said:

Peter, this is a common rim failure of Mavic MA-2 and Open 4CD rims. It is
caused NOT by overinflation but by a pressure pulse caused by hitting
something such as a stone or a pothole or such. The split rim is caused by
brake wear on the braking surface. If you look around the rim you'll
probably discover cracking or excessive wear in other sectors as well. And
if you look at the smaller failure you can see that it was caused by hitting
some sort of object. This is what caused the pressure pulse. But the rim was
on the edge of failure anyway and perhaps the real failure was caused by the
rim splitting from wear and the second damage was caused by your son trying
to save the bike and hitting something AFTER the failure.

If you look more closely at theoriginal photos you'll see that the rim is
not just bent outwards as an overpressure condition will cause, but is
rolled completely 180 degrees which can only be caused by hitting something
in the road.

Now, because the same act that bent the rim flatted the tire almost
instantly and since whatever caused it might have been a stone the same
color as the road and essentially invisible and may have been thrown off of
the road the victim might have no ability to detect that it was a stone save
from the perfectly clear interpretation of the damaged rim.

Dear Tom,

For what it's worth, the original Niterider posts pointed
out to the less observant (such as C. Fogel) that there was
no rim wear, since the wheel involved a hub brake, and he
had said so before nitwits like C. Fogel suggested rim wear.

(D'oh!)

(This may be quite different with Peter's son.)

Niterider also repeatedly insisted that he noticed no
impact.

(TMBQDWPS.)

And Niterider's tire exploded in his apartment, not on the
road.

(TMBQDWPS.)

(Possibly you mean the rim was bent out at 90 degrees, not
180 degrees?)

Whatever happened, it's still a curious situation.

Carl Fogel

Quoted message said:

Peter Cole writes:

[snip]

Quoted message said:

Quoted message said:

It's obvious to me that this failure was the result of overpressure
in the tire, pure and simple. That caused the rim to crack in 2
spots several inches apart, just as the hapless guy, who had his
integrity and intelligence questioned, claimed had happened to him.
A scenario that was declared by some to be impossible. Crow anyone?

He was not hapless. That should have been apparent by how he came on
and how rude he was in his responses. Don't cry for him.

[email hidden]

Dear Jobst,

I forget--did you suggest that Niterider was lying and
making it all up in your first or your second post in that
thread?

Carl Fogel

Peter Cole wrote

<snip> ... as the hapless guy, who had his integrity

Quoted message said:

and intelligence questioned, claimed had happened to him. A scenario
that was declared by some to be impossible. Crow anyone?

Yes, thank you.

Is she going to bring her guitar? And her boyfriend, what's his name?

Quoted message said:

Peter Cole said:

No, this is impossible. The failures occurred when the bike was
parked. The rim failures were so severe the bike could not have
been ridden with either of them. Whether the rim was worn or not is
beside the point. Two sections of that rim failed simultaneously
from overpressure. That's it. That's what happened to the OP as
well.

Now that you mention it. The ding in the rim to the right looks
almost exactly like the one Nitrider posted. In any case, if this
occurred while parked and no one present then it was most likely break
wear that weakened the sidewall of the rim enough for it to slit. The
ding on the right part of the picture was not caused by tire pressure
as most of the folks who commented on Nitrider's claims said. A
curled ding bent 90 degrees to the side was caused by an impact.

Quoted message said:

Quoted message said:

Now, because the same act that bent the rim flatted the tire almost
instantly and since whatever caused it might have been a stone the
same color as the road and essentially invisible and may have been
thrown off of the road the victim might have no ability to detect
that it was a stone save from the perfectly clear interpretation of
the damaged rim.

Quoted message said:

This was the interpretation that caused so much ill feeling. I
found it implausible then, impossible now.

Quoted message said:

As someone would say, you're clutching at straws.

If you are sure about this then you must have an explanation for how a
local 90 degree bend in a rim can occur.

Is it possible that the hook of the rim and the bead of the tire were locked
together well enough to deform the rim, but didn't blow out the tube until
reaching what appears to be more like 75 degrees or so. Whether or not this
was helped by a pinchflat-style rim dent is irrelevant.
--
Phil, Squid-in-Training

Peter Cole said:

Phil said:

This picture is a better picture than the other ones, since the
depth is more easily perceived than in the other ones. I don't see
how this couldn't have happened... all the factors point to tire
blow-off, namely a larger-volume tire, faulty gauge, a high-schooler,
hasty-prior-to-attending-school pumping, and a formidable pump with
plenty of capacity.

NiteRider's picture, however, shows a very short portion of rim
that's bent out. That's the big difference here. I think most of
us are thinking that the rim couldn't have blown out on such a small
circumference.

Niterider's rim had 2 identical failures a few inches apart.
Niterider's failure is about the same length of the second one on my
rim (fits between 2 spoke holes). I'm very sure both rims failed the
same way -- from overpressure and cracking. The surprising thing is
that the rim would crack in 2 sections simultaneously.

I find that interesting, also.

Kudos to your son for riding his bike at 16YO... most kids that age don't
think riding a bike to school is cool, and would much rather ride up in a
car instead.

--
Phil, Squid-in-Training

Quoted message said:

In any case, if this
occurred while parked and no one present then it was most likely

break

Quoted message said:

wear that weakened the sidewall of the rim enough for it to slit.

The

Quoted message said:

ding on the right part of the picture was not caused by tire pressure
as most of the folks who commented on Nitrider's claims said. A
curled ding bent 90 degrees to the side was caused by an impact.

One of my bikes suffered a rim failure of this kind while parked. I
had ridden a few miles from my house to get an insurance binder for my
car, and the bike was leaning against the window of the storefront that
housed the insurance agency. When the tire (which was a 700x28
inflated to some 140 psi) let go, several folks in the office took
shelter under their desks!

On examining the bike, I found that the sidewall of one of the bike's
rims had folded over. The area of failure was like that on the right
in Peter's photo, but it was perhaps 50% longer overall.

I will add that my bike's rim was just months old and had sidewall wear
that was negligible at most. It was a colorless matte anodized Mavic
261, which was a lightweight rim (for its sectional area) that had
relatively thin sidewalls.

There had been no braking anomalies on my ride immediately preceding
the blowout, so it was not a progressive failure. There had been no
impact damage to the rim before it failed.

Chalo Colina

chalo colina wrote:

When the tire (which was a 700x28

Quoted message said:

inflated to some 140 psi) let go, several folks in the office took
shelter under their desks!

On examining the bike, I found that the sidewall of one of the bike's
rims had folded over. The area of failure was like that on the right
in Peter's photo, but it was perhaps 50% longer overall.

Folded over or curled over? I can't tell from this picture which is the
case, but a blowout will certainly not curl the rim, as was the case
previously. Also, it's significant that the length of your failure was
considerably longer than the ones depicted here or previously.

Finally, did you have two failures in the rim or just one? These rims
have two failures, supposedly, miracle of miracles, simulataneous.

Dion Dock said:

I think you're seeing a failure caused by a worn out rim giving away.

I

Quoted message said:

don't have an explanation of why it occurred with no rider.

Compare it to "blowouts" caused by the tube being pinched between the

rim

Quoted message said:

and tire. Why don't they fail instantly or the moment you hit a

bump?

Quoted message said:

Perhaps you're not familiar with the previous thread. The question
involves whether overpressure could cause a rim (worn or otherwise) to
fail in that manner.

Werehatrack said:

In the case of your rim, however, the failure fits the pattern
observed in some other instances; a presumably worn rim, subjected to
enough pressure to shear the flange off, failed. As rims wear, the
pressure at which this can occur is gradually reduced. When the rim
wears enough for the failure point to be within the range of the
pressures generated by the compressor or pump, it fails, though
usually not right at the exact moment that the pressure is applied.
More often, the split happens several miles down the road, or even
hours later...but it's still a wear-related failure.

Again, the wear on the rim is not the issue. Of course the rim was worn
and probably wouldn't have failed if it wasn't! The point of contention
is not whether a worn/defective rim can fail that way, but whether
*any* rim can fail that way. It was judged impossible for the OP's
wheel to have failed in 2 spots simultaneously, even though it was
known to be a cheap rim that could easily have been flawed. The opinion
was also given (with the weight of <ahem> scientific fact) that a rim
could not deform like that from an overpressure failure, that it had to
be impact damage. Now, I'm hearing the same BS after having an
identical experience, and so is Chalo. I think both of us know a little
bit about bikes, materials and mechanics. Please try to keep your
responses on topic.

41 anonymously sniped:

Quoted message said:

You have only your son's word for what happened, which you
extracted via "interrogation",

OK, it's the "liar, liar, pant's on fire" argument. Brilliant! That's
what the OP heard. Don't forget to tell Chalo, too.

Thanks for the warmth.

A couple of new pictures:

Showing location of tube split:
<http://home.comcast.net/~peter_cole/tube.jpg>

Showing closeup of smaller failure:
<http://home.comcast.net/~peter_cole/closeup.jpg>

Same failure, from above:
<http://home.comcast.net/~peter_cole/closeabove.jpg>

Peter Cole said:

A couple of new pictures:

Showing location of tube split:
<http://home.comcast.net/~peter_cole/tube.jpg>

Showing closeup of smaller failure:
<http://home.comcast.net/~peter_cole/closeup.jpg>

Same failure, from above:
<http://home.comcast.net/~peter_cole/closeabove.jpg>

I think the picture with the split tube is revealing. It is as good as
a high speed movie or time-lapse series of photos. It shows that the
liftoff started between the 2 failed rim sections. The length of the
split corresponds to the length of the liftoff, which indicated that
the bead (wire) was over the rim and pressing down at both locations.
There would, of course, be no load in the center where the liftoff
started. Would the explosive decompression of the tube cause an impulse
load at the 2 spots the bead loaded the rim, or is it just the tension
in the bead with a fully inflated tire? Whatever, it was enough to
cause the simultaneous failures here, and doubtless the 2 failed rim
sections the OP found.

Peter Cole said:

Peter Cole said:

A couple of new pictures:

Showing location of tube split:
<http://home.comcast.net/~peter_cole/tube.jpg>

Showing closeup of smaller failure:
<http://home.comcast.net/~peter_cole/closeup.jpg>

Same failure, from above:
<http://home.comcast.net/~peter_cole/closeabove.jpg>

I think the picture with the split tube is revealing. It is as good

as

Quoted message said:

a high speed movie or time-lapse series of photos. It shows that the
liftoff started between the 2 failed rim sections. The length of the
split corresponds to the length of the liftoff, which indicated that
the bead (wire) was over the rim and pressing down at both locations.
There would, of course, be no load in the center where the liftoff
started. Would the explosive decompression of the tube cause an

impulse

Quoted message said:

load at the 2 spots the bead loaded the rim, or is it just the

tension

Quoted message said:

in the bead with a fully inflated tire? Whatever, it was enough to
cause the simultaneous failures here, and doubtless the 2 failed rim
sections the OP found.

Thinking about this some more, it seems that the tension in the bead
must increase during the period after the bead has lifted from the hook
and before the tube has expanded enough to lower the pressure. It's
likely that there is an instant when the bead tension peaks, it
supporting the area of sidewall that has disengaged from the rim hook.
I think this tension must be sufficient to fold/crack a weak rim. It
would do so at two spots, and these spots would be a reasonably
predictable distance apart. I don't think the similarities in that
regard between the OP's failure and mine are coincidental.