Re: Is my tire bad? - Page 2

NiteRider wrote:
> In article <%GL0e.81$pI4.71@fe07.usenetserver.com>, Phil,
> Squid-in-Training <phil_leeIHEARTBASHGUARDS@hotmail.com> wrote:
>
>> One of the first things to check would be if the sidewall was really
>> thin at that point, by machining or otherwise.
>
> Thank you! Finally somebody who doesn't just say, "You're an idiot and
> it can't possibly happen." Especially since none of these
> self-annointed "experts" are structural engineers.
>
> As I wrote, there may possibly be a manufacturing defect in this rim
> that weakened it at that point, but I don't have the tools to detect
> such a defect, such as a micrometer. All I can say definitively is
> that the rim wasn't bent like that when I mounted the tire but clearly
> displayed the damage after the tube blew inside my apartment.

I'm 21 and haven't settled into my air of superiority yet

On a serious note, you should be able to use your fingers to roughly gauge
the thickness of the rim at that point, even though it's blown out and
cracked. Check to see if other parts of the rim feel thin, too.
--
Phil, Squid-in-Training

NiteRider? writes:

>>>> http://server5.theimagehosting.com/i...g=rim_nite.jpg

>>>> I am certain that the damage on the pictured rim did not come
>>>> from tire inflation or a faulty tire bead. The damage was most
>>>> likely caused by hitting something lying on the road, like a one
>>>> inch high block of wood or other such obstacle, even a rock. It
>>>> most likely was not an excavation cover plate of step in the
>>>> pavement, because that would have damaged both edges of the rim.

>>>> Kevlar beads have no significant bending resistance and do not
>>>> blow out in this manner when inflated, nor did the wire bead
>>>> tires tested for clinch by cutting the wire at a number of
>>>> places. I wasn't there but I suspect you noticed the jolt and
>>>> assumed it was caused by the blowout. I believe the jolt caused
>>>> the blowout.

>>> Nice hypothesis, but completely wrong. This was the first rim,
>>> the first time this tire caused a problem for me. 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.

>> Well then its worse than I suspected. The rim could not be bent to
>> that shape with 60psi or even 120psi. If so, you need to explain
>> where the local force arose that cause this at this point dent and
>> nowhere else. I can't see your face or whether you are chuckling
>> as you write this, but the more I read the more I get the feeling
>> of a put-on (aka troll). Lateral force around the bead is uniform
>> when the wheel is not loaded, and couldn't possibly cause a local
>> irregularity. As I said, Kevlar bead tires have no bead stiffness
>> and press on the rim uniformly. There is no way your tire could
>> cause this anomaly.

>>> 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.

>> That it occurred the second time while riding ought to make you
>> wonder who bent the rim the first time, there being no damage to
>> the rim while it was loaded. I am certain that if air pressure
>> were the culprit then you could repeat the rim damage experiment by
>> inflating a tire to 120psi, something that folks report fairly
>> often in here. You might blow the tire off the rim if it isn't
>> properly mounted but even then it will not bend the rim, or for
>> that matter cause any damage.

As others have mentioned. the curled lip of the rim cannot have gotten
that way from air pressure, especially when not in use. You are
drawing the conclusion that only a non-observant rider could do this.
No one put that proposition forward in response to your questions.

That there is a crack inside the sidewall of the rim is not proof of
anything other than that the force that curled the rim was strong
enough to produce such a curl, one that no one here has ever seen
without external mechanical interventions, aka witting an obstacle.

As I said, if it was caused by tire inflation then how come there was
no damage on the second occurrence? There is no way a tire can cause
this damage regardless of how poorly it is made. At worst it wold not
stay on the rim, but damaging the rim is not a result of that. The
curl is so rounded that a tire wold locally detach before it got to
that state. There being no holding force left in the rim once it
angles out 30 degrees or so would make further rim deformation an
impossibility.

There is something else afoot here and it is not apparent without more
information especially because the question was formatted in such a
mechanically contradictory manner. In other posts it appears that
this is not the first rim, wheel or tire you have ridden and that many
years have passed with much experience. In that event I wonder why
you need to ask and then reject assessments that you get.

I don't think further pictures will make any difference in what people
on this end of the inquiry can offer.

Jobst.Brandt@stanfordalumni.org

On Fri, 25 Mar 2005 16:22:15 GMT, NiteRider
<stingray@bowlander.bike> wrote:

>In article <1111725186.d619ca0428f1215011e3c92046f7cf1d@teranews>, jim
>beam <nospam@example.net> wrote:
>
>> the no-name rim bent because it was weak/defective - as evidenced by
>> having the same tire blowing out again, it did not bend the better
>> quality campy rim. the tire blew because it's got a bead defect. it's
>> unfortunate coincidence you got the first two in the same place at the
>> same time.
>
>You're right. Now that I think about it, the bead did work off on the
>left (non-drivetrain) side in both blowouts. It can't be coincidence
>and both rims can't be bad.
>
>> please note however, that regardless of the pressure rating
>> on the tire sidewall, the wider the tire, the lower the pressure the rim
>> can take. you don't state the tire width in your original post, but
>> check out mavic's web site for a table that shows this relationship.
>
>I can't find the table on Mavic's confusing website, unless it's in the
>"technical manual" available to registered users only. The tire was the
>widest Metro I could get, 26x2.0, which I liked to run at 80psi.
>
>> best, safest thing to do is discard those tires. you don't want that
>> same experience with the front blowing out on a descent.
>>
>> regarding "garage" blowouts, i've had almost identical experience with
>> cheapo kenda tires & some other no-name brand, i forget which. just
>> thrown them as far away as possible. and cut the bead before hand so
>> noone else can salvage them. these days i stick with "known" tire
>> brands like michelin, hutchinson, continental, etc. [my hutchinsons
>> have been /fantastic/ for winter puncture resistance btw.]
>
>That's why I asked here. People have said they've had no problems with
>IRC tires, so it must be just this one tire that has a problem.

Dear NiteRider,

The secret login and password for this site:

http://www.tech-mavic.com/

is mavic-com and dealer.

Security is dreadfully important, so please don't tell
anyone else.

Carl Fogel

NiteRider Stingray Bowlander Huh? writes from cover of darkness:

>> The secret login and password for this site:

http://www.tech-mavic.com/

>> is mavic-com and dealer.

>> Security is dreadfully important, so please don't tell anyone else.

> Thanks. Took a while, but I found the file. Mavic only recommends
> 60-odd psi max for a 2.0 tire, eh? That's pretty low.

That pressure limit is not for rim protection but rather to prevent
tire blow-off. Blow-off force is proportional to tire pressure times
inside rim width per unit length around the rim and you'll see by this
rule it corresponds to the pressure given for narrower rims, the bead
retaining force being the same for small and large tires.

Jobst.Brandt@stanfordalumni.org

NiteRider wrote:
> In article <8cm841tapugjad73qprrdm1rfmtngglfir@4ax.com>,
> <carlfogel@comcast.net> wrote:
>
>
>>Dear NiteRider,
>>
>>The secret login and password for this site:
>>
>>http://www.tech-mavic.com/
>>
>>is mavic-com and dealer.
>>
>>Security is dreadfully important, so please don't tell
>>anyone else.
>
>
> Thanks. Took a while, but I found the file. Mavic only recommends
> 60-odd psi max for a 2.0 tire, eh? That's pretty low.

jobst is right regarding pressure comparison. 80psi for a 2.0 is too high.

note however that pressure /does/ exert a "separation" load between the
rim beads, in the orientation that the rim is weakest, its extrusion
axis. mavic's pressure limits may not be exactly applicable to all
other rims, but if you follow them, you'll be in a safer ballpark than
where you are presently. if high pressure/lower rolling resistance is
important, consider skinnier tires.

jobst.brandt@stanfordalumni.org wrote:
> NiteRider Stingray Bowlander Huh? writes from cover of darkness:
>
>
>>>The secret login and password for this site:
>
>
> http://www.tech-mavic.com/
>
>
>>>is mavic-com and dealer.
>
>
>
>>>Security is dreadfully important, so please don't tell anyone else.
>
>
>>Thanks. Took a while, but I found the file. Mavic only recommends
>>60-odd psi max for a 2.0 tire, eh? That's pretty low.
>
>
> That pressure limit is not for rim protection but rather to prevent
> tire blow-off.

it does help with tire blow off, but there /is/ a rim protection
component as well. tire pressure loading is perpendicular to the rim's
weakest [extrusion] axis - fatigue strength in this orientation is
significantly worse.

> Blow-off force is proportional to tire pressure times
> inside rim width per unit length around the rim and you'll see by this
> rule it corresponds to the pressure given for narrower rims, the bead
> retaining force being the same for small and large tires.
>
> Jobst.Brandt@stanfordalumni.org

NiteRider wrote:
> In article <1111940728.d9df245324d78132f76829d5ab9318ff@teranews>, jim
> beam <nospam@example.net> wrote:
>
>
>>jobst is right regarding pressure comparison. 80psi for a 2.0 is too high.
>
>
> Which makes me wonder why IRC's pressure recommendations on the
> sidewall say 45-85 psi. As I recall, somebody (maybe it was Frank
> Berto) once wrote that a tire shouldn't blow off a rim until it reaches
> roughly twice the maximum recommended pressure.

that's a /should/, not a /does/. tire quality is not a constant. and
as discussed before, you've got a defective tire.

>
>
>>note however that pressure /does/ exert a "separation" load between the
>>rim beads, in the orientation that the rim is weakest, its extrusion
>>axis. mavic's pressure limits may not be exactly applicable to all
>>other rims, but if you follow them, you'll be in a safer ballpark than
>>where you are presently. if high pressure/lower rolling resistance is
>>important, consider skinnier tires.
>
>
> I'm more interested in rim protection. I do long, moderately high speed
> descents (30-35 mph) on bad roads and I don't always have time to stand
> up when a bump or pothole approaches. I have a RockShox, but it's a
> hardtail. I guess I can drop it to 70psi, but I wouldn't be comfortable
> with much less than that.

if you're road riding, i wouldn't worry. i'm just over 200# and ride my
conti vertical pros at 35psi over rock. sometimes less if i can't be
bothered to pump. touch wood, i've never had a pinch flat in the 2
years i've been riding them. admittedly, they're 2.3", not 2.0", but
even so, i think anything over about 50psi on a 2" fattie is excessive.

>
> Noticed something else that blows Brandt's hypothesis out of the water.
> I'd never really closely inspected that rim once I saw the dent and
> knew it was toast. Taking a closer look at it a couple of days ago,
> there are actually *two* such bends in the rim flange, spaced about 12
> inches apart. They look identical, which is probably why I never
> noticed there was more than one. There's no way one rock could make two
> identical dents even if I'd been riding it, which I wasn't. My theory
> is that the badly installed bead started working off. I think, but I
> can't quite remember, that I saw the tube start to bulge out from under
> the bead section that was outside the rim, but it blew a second later,
> before I could detach the pump and relieve the pressure. Before this
> point, the pressure around the tire would have been pushing the tire in
> all directions radially from the hub, trying to stretch the bead. The
> two contact points where the bead crossed over from the inside to the
> outside of the rim had the aggregate force from all this pressure
> bearing down on them and failed catastropically.

lower pressure sir. but look at it another way - you've got one rim
upgrade out of this learning experience. if you're a good student, your
second rim upgrade will be voluntary, not compulsory.

On Sun, 27 Mar 2005 17:29:21 -0800, jim beam
<nospam@example.net> wrote:

>NiteRider wrote:
>> In article <1111940728.d9df245324d78132f76829d5ab9318ff@teranews>, jim
>> beam <nospam@example.net> wrote:
>>
>>
>>>jobst is right regarding pressure comparison. 80psi for a 2.0 is too high.
>>
>>
>> Which makes me wonder why IRC's pressure recommendations on the
>> sidewall say 45-85 psi. As I recall, somebody (maybe it was Frank
>> Berto) once wrote that a tire shouldn't blow off a rim until it reaches
>> roughly twice the maximum recommended pressure.
>
>that's a /should/, not a /does/. tire quality is not a constant. and
>as discussed before, you've got a defective tire.
>
>>
>>
>>>note however that pressure /does/ exert a "separation" load between the
>>>rim beads, in the orientation that the rim is weakest, its extrusion
>>>axis. mavic's pressure limits may not be exactly applicable to all
>>>other rims, but if you follow them, you'll be in a safer ballpark than
>>>where you are presently. if high pressure/lower rolling resistance is
>>>important, consider skinnier tires.
>>
>>
>> I'm more interested in rim protection. I do long, moderately high speed
>> descents (30-35 mph) on bad roads and I don't always have time to stand
>> up when a bump or pothole approaches. I have a RockShox, but it's a
>> hardtail. I guess I can drop it to 70psi, but I wouldn't be comfortable
>> with much less than that.
>
>if you're road riding, i wouldn't worry. i'm just over 200# and ride my
>conti vertical pros at 35psi over rock. sometimes less if i can't be
>bothered to pump. touch wood, i've never had a pinch flat in the 2
>years i've been riding them. admittedly, they're 2.3", not 2.0", but
>even so, i think anything over about 50psi on a 2" fattie is excessive.
>
>>
>> Noticed something else that blows Brandt's hypothesis out of the water.
>> I'd never really closely inspected that rim once I saw the dent and
>> knew it was toast. Taking a closer look at it a couple of days ago,
>> there are actually *two* such bends in the rim flange, spaced about 12
>> inches apart. They look identical, which is probably why I never
>> noticed there was more than one. There's no way one rock could make two
>> identical dents even if I'd been riding it, which I wasn't. My theory
>> is that the badly installed bead started working off. I think, but I
>> can't quite remember, that I saw the tube start to bulge out from under
>> the bead section that was outside the rim, but it blew a second later,
>> before I could detach the pump and relieve the pressure. Before this
>> point, the pressure around the tire would have been pushing the tire in
>> all directions radially from the hub, trying to stretch the bead. The
>> two contact points where the bead crossed over from the inside to the
>> outside of the rim had the aggregate force from all this pressure
>> bearing down on them and failed catastropically.
>
>lower pressure sir. but look at it another way - you've got one rim
>upgrade out of this learning experience. if you're a good student, your
>second rim upgrade will be voluntary, not compulsory.

Dear Jim,

Just for the fun of comparison, 6 psi works fine fore and
aft on 21x2.75 and 18x4.00 trials tires with 200-lb riders
on 220-lb motorcycles for rough trail riding. Of course, the
motorcycle tires have rather higher and stiffer sidewalls.

Carl Fogel

> In article <1111940728.d9df245324d78132f76829d5ab9318ff@teranews>, jim
> beam <nospam@example.net> wrote:
>>jobst is right regarding pressure comparison. 80psi for a 2.0 is too high.
> Which makes me wonder why IRC's pressure recommendations on the
> sidewall say 45-85 psi. As I recall, somebody (maybe it was Frank
> Berto) once wrote that a tire shouldn't blow off a rim until it reaches
> roughly twice the maximum recommended pressure.

>>note however that pressure /does/ exert a "separation" load between the
>>rim beads, in the orientation that the rim is weakest, its extrusion
>>axis. mavic's pressure limits may not be exactly applicable to all
>>other rims, but if you follow them, you'll be in a safer ballpark than
>>where you are presently. if high pressure/lower rolling resistance is
>>important, consider skinnier tires.

NiteRider wrote:
> I'm more interested in rim protection. I do long, moderately high speed
> descents (30-35 mph) on bad roads and I don't always have time to stand
> up when a bump or pothole approaches. I have a RockShox, but it's a
> hardtail. I guess I can drop it to 70psi, but I wouldn't be comfortable
> with much less than that.
>
> Noticed something else that blows Brandt's hypothesis out of the water.
> I'd never really closely inspected that rim once I saw the dent and
> knew it was toast. Taking a closer look at it a couple of days ago,
> there are actually *two* such bends in the rim flange, spaced about 12
> inches apart. They look identical, which is probably why I never
> noticed there was more than one. There's no way one rock could make two
> identical dents even if I'd been riding it, which I wasn't. My theory
> is that the badly installed bead started working off. I think, but I
> can't quite remember, that I saw the tube start to bulge out from under
> the bead section that was outside the rim, but it blew a second later,
> before I could detach the pump and relieve the pressure. Before this
> point, the pressure around the tire would have been pushing the tire in
> all directions radially from the hub, trying to stretch the bead. The
> two contact points where the bead crossed over from the inside to the
> outside of the rim had the aggregate force from all this pressure
> bearing down on them and failed catastropically.

I do not believe that you can damage a rim by inflation
pressure of 80psi no matter how poorly mounted.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

NiteRider <stingray@bowlander.bike> writes:

> 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.

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.

Jim Smith <3.141592six@gmail.com> wrote:

>NiteRider <stingray@bowlander.bike> writes:
>
>> 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.
>
>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.

Yeah . . . I could be way off the mark, but I've got a pretty clear
and detailed image of this NiteRider guy . . . and it's nothing to be
proud of.

NiteRider: you may want to examine your approach: combative and
indignant aren't going to leave you open to learning around here . . .
and there are many from whom you could learn if you chose to.

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.

Carl Fogel

NiteRider snipes from cover:

>> 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.

So why do you come to this forum if you have the answers? You may
think you know what happened, but you don't. Your responses are no
affirmation that you are a person seeking advice either.

Jobst.Brandt@stanfordalumni.org

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

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