Total wheel Failure

Quoted message said:

Quoted message said:

Quoted message said:

On 7 Jun 2006 08:08:23 -0700, [email hidden] wrote:

> How many of you would put an identical wheel/tire/pressure in as a
> replacement and continue riding?

Dear D.,

I wouldn't put a 37mm tire on a rim recommended for no more than
28mm and 117 psi and then blow it up to an estimated 80-85 psi,
particularly if I weighed 275 lbs.

I've heard of a case where the wheel failed catastrophically within
500 miles on smooth pavement when this was done.

Cheers,

Carl Fogel

How about a 28mm tire?

Dear D.,

I'd happily put a 28mm tire on a rim rated for that width with no more
than 117 psi--and inflate it to about 100 psi or less. A recommended
maximum is a warning, not an invitation to see what happens.

In any case, the destroyed rim was wearing a 37mm tire inflated to an
estimated 80-85 psi when it abruptly tore itself in half after only
500 miles.

That 37mm is 32% beyond the CXP33's maximum recommended width.

What could be a more impressive and dramatic illustration that Mavic
was right about those rim limits? Or that wider tires exert more
leverage on rims?

Cheers,

Carl Fogel

Carl, have you ever seen this type of failure before?

How many large people in the world put 37mm tires on their CXP33s, and pump
them up to 85psi? I am willing to bet more than one.

IMO, this is a manufacturing defect.
--
Phil

Quoted message said:

Quoted message said:

Quoted message said:

I'm planning on having all my wheels rebuilt with different rims

Quoted message said:

Briefly, that would be dumb and wasteful

Why? If the Mavics have quality control problems, isn't it possible
that the remaining rims could likely fail also?

Ignore him. He's a Francoshill.

Greg
--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

Phil said:

Quoted message said:

Quoted message said:

[email hidden] wrote:

>On 7 Jun 2006 08:08:23 -0700, [email hidden] wrote:
>
>
>>How many of you would put an identical wheel/tire/pressure in as a
>>replacement and continue riding?
>
>Dear D.,
>
>I wouldn't put a 37mm tire on a rim recommended for no more than
>28mm and 117 psi and then blow it up to an estimated 80-85 psi,
>particularly if I weighed 275 lbs.
>
>I've heard of a case where the wheel failed catastrophically within
>500 miles on smooth pavement when this was done.
>
>Cheers,
>
>Carl Fogel

How about a 28mm tire?

Dear D.,

I'd happily put a 28mm tire on a rim rated for that width with no more
than 117 psi--and inflate it to about 100 psi or less. A recommended
maximum is a warning, not an invitation to see what happens.

In any case, the destroyed rim was wearing a 37mm tire inflated to an
estimated 80-85 psi when it abruptly tore itself in half after only
500 miles.

That 37mm is 32% beyond the CXP33's maximum recommended width.

What could be a more impressive and dramatic illustration that Mavic
was right about those rim limits? Or that wider tires exert more
leverage on rims?

Cheers,

Carl Fogel

Carl, have you ever seen this type of failure before?

How many large people in the world put 37mm tires on their CXP33s, and pump
them up to 85psi? I am willing to bet more than one.

IMO, this is a manufacturing defect.

I'm not 275 but I've been know to run fat tires at high pressure on
narrow rims. I never thought they'd just blow up. In fact I never
thought they'd even fail. I guess MA-2s were made when Mavic still had
quality control.

Greg

--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

Squid-in-Training said:

Quoted message said:

Quoted message said:

[email hidden] wrote:
> On 7 Jun 2006 08:08:23 -0700, [email hidden] wrote:
>
>> How many of you would put an identical wheel/tire/pressure in as a
>> replacement and continue riding?
>
> Dear D.,
>
> I wouldn't put a 37mm tire on a rim recommended for no more than
> 28mm and 117 psi and then blow it up to an estimated 80-85 psi,
> particularly if I weighed 275 lbs.
>
> I've heard of a case where the wheel failed catastrophically within
> 500 miles on smooth pavement when this was done.
>
> Cheers,
>
> Carl Fogel

How about a 28mm tire?

Dear D.,

I'd happily put a 28mm tire on a rim rated for that width with no more
than 117 psi--and inflate it to about 100 psi or less. A recommended
maximum is a warning, not an invitation to see what happens.

In any case, the destroyed rim was wearing a 37mm tire inflated to an
estimated 80-85 psi when it abruptly tore itself in half after only
500 miles.

That 37mm is 32% beyond the CXP33's maximum recommended width.

What could be a more impressive and dramatic illustration that Mavic
was right about those rim limits? Or that wider tires exert more
leverage on rims?

Cheers,

Carl Fogel

Carl, have you ever seen this type of failure before?

How many large people in the world put 37mm tires on their CXP33s, and pump
them up to 85psi? I am willing to bet more than one.

IMO, this is a manufacturing defect.

Dear Phil,

No, I've never seen a rim tear itself into two pieces on a smooth
piece of pavement. No one else who's posted has mentioned seeing such
as thing, either, though I expect there are riders who have indeed
seen such failures.

I think that you'd lose your bet.

Think about why Mavic clearly shows safe recommended rim pressures
declining from 146 psi to 117 psi as tire width increases from 19 to
28 mm:

http://www.mavic.com/ewb_pages/p/produit_jante_cxp33.php?onglet=3&gamme=route

Going to a 37mm is about 32% off the manufacturer's scale. Draw a
graph of the four data points, and you get a steeper and steeper
curve. A line drawn between the last two points indicates that 65 psi
would be the maximum safe pressure for a 37mm tire--and that's a
straight line, not the actual diving curve. Any spreadsheet will show
this in a few minutes. Slap a ruler on the last two data points and
see where it ends up over 37mm.

Here's a cross-section diagram of the CXP33:

lickbike.comproductpage.aspxOpen ↗

On my screen, the "19.4mm" exterior width measures 41mm, while the
unlabeled interior width measures 29.5mm.

Scaling indicates that the interior width is only 14mm.

Here's Georg Boeger's well-respected German tandem site's rim/tire
size chart, way up near the top of the page:

http://tandem-fahren.de/Technik/Reifentips/index.html

Here's the edited version, way down on Sheldon's page:

http://www.sheldonbrown.com/tire_sizing.html

If dimension "a" is 14mm (between 13 and 15), then Boeger estimates
that a 37mm tire is about 3 bombs to the right on the warning scale.

The bombs aren't a joke--that's how the an aluminum rim will fail when
overstressed by the leverage of the wrong tire inflated too high. It's
basically a thin-walled pressure vessel.

The rim section under the hub is squashing out abruptly to the sides
as its center flattens at the contact patch. Then it "relaxes" and
spins around again for the next stress rise.

All the time, it's under the tremendous expansion pressure of the
inner tube.

Eventually, ka-boom! About 500 miles in this case.

The wider the bicycle tire and the narrower the rim, the lower the
safe inflation pressure.

Add a rider who weighs twice as much as you do, and 500 miles later
the rim fails dramatically, just as expected.

Darned few riders weighing 265 lbs are likely to be putting 37mm tires
at 80-85 psi on such a narrow rim. The ones who do are going to find
out the hard way that it's a very bad idea.

The posters who are surprised are generally riding 35mm or smaller
tires (that 2mmm matters), using 75% or less as much pressure (20 to
40 psi makes a big difference down that low), and don't weigh 265 lbs
(60 to 130 pounds less is a considerable change).

As I've said before, can you think of a more dramatic illustration of
the warnings about tire width and inflation?

Cheers,

Carl Fogel

Quoted message said:

I suggest the rider needs a 500+ g rim, such as at minimum an Ambrosio
Evolution (480g, 13.5mm

Quoted message said:

ERTRO width, <http://www.ambrosiospa.com/cerchi_corsa.htm>😉, much better an Ambrosio Keba (610g, 18mm ERTRO width, <http://www.a mbrosiospa.com/touring.htm>😉.

Hi! I'm the clydesdale whose Mavic blew up, instigating this thread.
I'm planning on having all my wheels rebuilt with different rims (I'm
scared of those Mavics now...). I'm not familiar with Ambrosio rims.
I note that Ambrosio offers multiple "touring" rims with wider
profiles. What differences are there between the different Ambrosio
touring rims, and which is the strongest?

The person you really want to correspond with is Chalo Cholina of this
forum, the heaviest serious rider on the internet, if not the planet.
On the way to that distinction he spent enough time at your weight to
know exactly what will last and what will not. You will find Ambrosio
rims a little hard to come by in the US, and I believe he uses Sun
rims. These come or at least used to come in suitably strong models
(CR-18, CR-16, Rhyno and Rhyno Lite) but they don't have double eyelets
and sockets, which is not quite as desirable. Another suitable rim
would likely be the Rigida Sphinx, also unavailable in 700C in the US.
You will find instead Mavic touring rims that have the right basic
specs, but they are expensive and I believe Mr Cholina has a low
opinion of them. Velocity rims also have a good reputation but are also
single eyeletted and I don't know the models.

You and your builder were fooled by Mavic into thinking the rim was
strong because of the 36 holes and the aero profile. An aero profile
makes for a stiff rim, but the strength to weight ratio is not as good
as a box section with double eyelets. People confuse stiffness with
strength and durability. They are not the same, the classic extreme
example being styrofoam. Now that we have an "exploded view" of the
innards of the CXP33, thanks to you, we can see that in fact it is not
a strong rim, the walls, from your photograph, appearing to be
extremely thin. They have to be, to get a 460g rim in that cross
section. Compare the cross sections at
<www.ambrosiospa.com/cerchi_corsa.htm>, and you will see that their
comparable model, the Balance, is 500g, and it already has much thinner
walls than the 460g Excellence or the 480g Evolution, in turn both
thicker than the 430g Excellight. Probably the Evolution with 32mm
tires at 90 psi would work for you, without a heavy load, but you
should check with Chalo to be sure.

I certainly would not use your wheels at your weight, even if the tire
size and pressure were within spec. I suggest returning the wheels to
the builder or selling them on eBay. One would expect them to be fine
only for someone much lighter.

As for the heavier Ambrosio touring rims, the strongest, according to
the weight and the fact that it is a box section with double eyelets
and sockets, would be the C.C. 28. You can see from the cross section
that it has very thick walls, and the weight is correspondingly high. I
doubt you really need this strong a rim, unless you are touring with a
heavy load. I haven't used it or the Keba, but the Keba is similar to
the model no longer available I do use from a different manufacturer, a
smaller and lighter (~560g) 622-17. But I weigh much less than you.

On this forum Jobst has described some terrible accidents, one where
the rider went backwards onto a rear wheel. It's not something you want
to do. I think you are fortunate to have escaped disastrous injury. The
wheels you have are evidently not suitable for you and you need to find
something better, or else start planning your funeral.

On Wed, 07 Jun 2006 23:22:05 -0700, "G.T." <[email hidden]>

Quoted message said:

Phil said:

Quoted message said:

On 7 Jun 2006 12:07:36 -0700, [email hidden] wrote:

>[email hidden] wrote:
>
>>On 7 Jun 2006 08:08:23 -0700, [email hidden] wrote:
>>
>>
>>>How many of you would put an identical wheel/tire/pressure in as a
>>>replacement and continue riding?
>>
>>Dear D.,
>>
>>I wouldn't put a 37mm tire on a rim recommended for no more than
>>28mm and 117 psi and then blow it up to an estimated 80-85 psi,
>>particularly if I weighed 275 lbs.
>>
>>I've heard of a case where the wheel failed catastrophically within
>>500 miles on smooth pavement when this was done.
>>
>>Cheers,
>>
>>Carl Fogel
>
>How about a 28mm tire?

Dear D.,

I'd happily put a 28mm tire on a rim rated for that width with no more
than 117 psi--and inflate it to about 100 psi or less. A recommended
maximum is a warning, not an invitation to see what happens.

In any case, the destroyed rim was wearing a 37mm tire inflated to an
estimated 80-85 psi when it abruptly tore itself in half after only
500 miles.

That 37mm is 32% beyond the CXP33's maximum recommended width.

What could be a more impressive and dramatic illustration that Mavic
was right about those rim limits? Or that wider tires exert more
leverage on rims?

Cheers,

Carl Fogel

Carl, have you ever seen this type of failure before?

How many large people in the world put 37mm tires on their CXP33s, and pump
them up to 85psi? I am willing to bet more than one.

IMO, this is a manufacturing defect.

I'm not 275 but I've been know to run fat tires at high pressure on
narrow rims. I never thought they'd just blow up. In fact I never
thought they'd even fail. I guess MA-2s were made when Mavic still had
quality control.

Greg

Dear Greg,

Well, that raises a few questions . . .

How much short of 275 lbs?

Tires as fat as 37mm on a rim with an apparent interior diameter of
14mm? Or only the 35 and 32mm models that most posters have mentioned?

Pressures as high as 80-85 psi ("estimated" by thumb tests, which
leaves even higher pressures quite possible)?

The CXP33 has apparent exterior/interior widths of 19.4/14 mm, judging
by this cross-section:

lickbike.comproductpage.aspxOpen ↗

Any idea what those dimensions are on an MA2? I won't be surprised if
the two rims are similar, but those first 3 questions are probably
more important.

Cheers,

Carl Fogel

Quoted message said:

On Wed, 07 Jun 2006 23:22:05 -0700, "G.T." <[email hidden]>

Quoted message said:

Phil said:

[email hidden] wrote:

>On 7 Jun 2006 12:07:36 -0700, [email hidden] wrote:
>
>
>
>>[email hidden] wrote:
>>
>>
>>>On 7 Jun 2006 08:08:23 -0700, [email hidden] wrote:
>>>
>>>
>>>
>>>>How many of you would put an identical wheel/tire/pressure in as a
>>>>replacement and continue riding?
>>>
>>>Dear D.,
>>>
>>>I wouldn't put a 37mm tire on a rim recommended for no more than
>>>28mm and 117 psi and then blow it up to an estimated 80-85 psi,
>>>particularly if I weighed 275 lbs.
>>>
>>>I've heard of a case where the wheel failed catastrophically within
>>>500 miles on smooth pavement when this was done.
>>>
>>>Cheers,
>>>
>>>Carl Fogel
>>
>>How about a 28mm tire?
>
>Dear D.,
>
>I'd happily put a 28mm tire on a rim rated for that width with no more
>than 117 psi--and inflate it to about 100 psi or less. A recommended
>maximum is a warning, not an invitation to see what happens.
>
>In any case, the destroyed rim was wearing a 37mm tire inflated to an
>estimated 80-85 psi when it abruptly tore itself in half after only
>500 miles.
>
>That 37mm is 32% beyond the CXP33's maximum recommended width.
>
>What could be a more impressive and dramatic illustration that Mavic
>was right about those rim limits? Or that wider tires exert more
>leverage on rims?
>
>Cheers,
>
>Carl Fogel

Carl, have you ever seen this type of failure before?

How many large people in the world put 37mm tires on their CXP33s, and pump
them up to 85psi? I am willing to bet more than one.

IMO, this is a manufacturing defect.

I'm not 275 but I've been know to run fat tires at high pressure on
narrow rims. I never thought they'd just blow up. In fact I never
thought they'd even fail. I guess MA-2s were made when Mavic still had
quality control.

Greg

Dear Greg,

Well, that raises a few questions . . .

How much short of 275 lbs?

50.

Quoted message said:

Tires as fat as 37mm on a rim with an apparent interior diameter of
14mm? Or only the 35 and 32mm models that most posters have mentioned?

55mm mtn bike tires.

Quoted message said:

Pressures as high as 80-85 psi ("estimated" by thumb tests, which
leaves even higher pressures quite possible)?

No, up to 70 psi with a gauge.

Quoted message said:

The CXP33 has apparent exterior/interior widths of 19.4/14 mm, judging
by this cross-section:

lickbike.comproductpage.aspxOpen ↗

Any idea what those dimensions are on an MA2? I won't be surprised if
the two rims are similar, but those first 3 questions are probably
more important.

Don't know. And I don't recall seeing tables with max pressure per tire
width for the MA-2.

Greg

--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

41 said:

ss
section. Compare the cross sections at
<www.ambrosiospa.com/cerchi_corsa.htm>, and you will see that their
comparable model, the Balance, is 500g, and it already has much thinner
walls than the 460g Excellence or the 480g Evolution, in turn both
thicker than the 430g Excellight.

Has anyone ever given a thought that a rim is under very severe stress
upon braking, which does not necessarily go with the rider's weight,
and that a thin wall and a non-boxed geometry are really bad features
in that regard?

Sergio
Pisa

41 said:

If we plot hoop force per unit length as caculated by a previous poster
as P*R, versus tire size, the results are not a horizontal line. The
figures (force in megaN) are:

mm psi MN/m
19 146 9.56 (spec)
23 138 10.94 (spec)
25 131 11.29 (spec)
28 117 11.29 (spec)
35 88 10.62 (spec)
37 85 10.84 (catastrophic failure)

That shows it : the 37mm@85psi configuration puts (a tad) less stress
on the rim walls than a Mavic-acceptable (and quite common)
23mm@138psi.
So, this configuration alone cannot be a single cause for the failure,
but the high-side load generated may be a contributive factor.

On the other hand, rider weight can also be a factor according to
Mavic's documentation. I can not find it again on Mavic's website, but
I found the following downloaded 2-3 years ago (original in french, I
tried to translate) :

"Mavic recommends that the total weight of the biker and his gear does
not exceeds the following :
- Road rims : 100 kg (except MA3 : 85 kg) ;
- MTB rims :
- 75 kg on X517 ;
- 90 kg on X139, X139 Disc, X221, X223 Disc, X225, X 317 Disc,
X618, X3.1 and X3.1 Disc ;
- 115 kg on F219 Disc, F519, D521, D321 Disc and D3.1 Disc.
- Asphalt [touring] rims : 105 kg on T223 and T224, 125 kg on T520."

So the 275lb rider (that makes around 125kg or am I wrong?) could only
use the T520 rim in the Mavic Range.... and taking into account the
bike weight, he should go elsewhere.
It was definitively written as a recommendation, not a warranty limit,
but according to that data any Mavic road rim should not be used with a
total weight of more than 220lb, ie a rider weight of more than
190-200lb, with the exception of MA3 rim limited at 185/160lb.

Imho, the main factor of the catastrophic failure could well be a
pre-existing defect, either a manufacturing one or a previous
unremarked shock, with the higher-than-recommended load as a
contributing factor.

Quoted message said:

I suggest the rider needs a 500+ g rim,

Sounds very sensible according to the above.

Quoted message said:

That shows it : the 37mm@85psi configuration puts (a tad) less stress
on the rim walls than a Mavic-acceptable (and quite common)
23mm@138psi.

That's exactly what I thought, without looking at any specs in fact (if
you can, read my post on it in it.sport.cuclismo).
The stress on the rim from the inflated tube depends on the inflation
pressure and the width of the bed onto which the tube pushes. It has
nothing to do with how large the tube and tire are outside of the rim.

At least, this is what makes sense to me.

Sergio
Pisa

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

Quoted message said:

Not mine, but a friends.

Your thoughts?

Currently the server is slow, so it may take a bit to load.

http://bikeforums.net/showthread.php?t=201510

I thought about it some more, and I think that since it was mentioned that
the tube had a inner tear hole from where it blew out at.
That either you have a rim strip that wasn't protecting the tube from the
spoke holes as expected, or the tire slipped off the rim at one point
causing the tube to fail, and then the sudden release of air pressure
coupled with a maybe overtensioned wheel, along with the rider's weight and
power pedaling along, made the wheel taco. At that point pedaling along
under power the wheel jammed in the frame or brakes and had the total
failure collapse like you show in the pictures.
I suspect one culprit is the use of narrow road bike rims with big wide
tires, the tire sides are at a angle and maybe don't get hooked well, plus
the tube doesn't get down into the tire rim area very well and maybe doesn't
put enough pressure on the tire bead to help lock it in place.
Thus wider rims and making sure the rim tape is wide and good for the rim
would seem to me to be the solution to preventing this from happening again.

Quoted message said:

Imho, the main factor of the catastrophic failure could well be a
pre-existing defect, either a manufacturing one or a previous
unremarked shock, with the higher-than-recommended load as a
contributing factor.

Quoted message said:

I suggest the rider needs a 500+ g rim,

Sounds very sensible according to the above.

I weigh 230. My strategy has always been to (where possible) use
components rated for heavy duty, like touring stuff for road bikes and
DH stuff for off-road. I think it makes sense to spec bike weight as a
fraction of rider weight, and that goes double for wheels, which are
often the most problematic component for heavy riders.

I mostly use Mavic touring rims on my road bikes, just to manage my own
weight. I have used lighter rims, but only in a box section. I have used
those lighter rims with over-size tires (35mm studs), but I inflate them
only to 65psi. I inspect rims regularly, measure sidewall wear, and am
conservative about retiring them.

Heavy riders should stay away from lightweight components, a rider
that's 50% heavier than nominal should be using a rim that's much
heavier than nominal -- it's that simple.

Quoted message said:

41 said:

If we plot hoop force per unit length as caculated by a previous poster
as P*R, versus tire size, the results are not a horizontal line. The
figures (force in megaN) are:

mm psi MN/m
19 146 9.56 (spec)
23 138 10.94 (spec)
25 131 11.29 (spec)
28 117 11.29 (spec)
35 88 10.62 (spec)
37 85 10.84 (catastrophic failure)

By the way, sorry, make those kiloNewtons.

Quoted message said:

That shows it : the 37mm@85psi configuration puts (a tad) less stress
on the rim walls than a Mavic-acceptable (and quite common)
23mm@138psi.
So, this configuration alone cannot be a single cause for the failure,
but the high-side load generated may be a contributive factor.

I note that the 55/70psi used by another poster here gives 13.3 kN on
an MA2, same interior width (13.5mm) as the CXP33. I believe this shows
just how much stronger the MA2 is.

Quoted message said:

On the other hand, rider weight can also be a factor according to
Mavic's documentation. I can not find it again on Mavic's website, but
I found the following downloaded 2-3 years ago (original in french, I
tried to translate) :

"Mavic recommends that the total weight of the biker and his gear does
not exceeds the following :
- Road rims : 100 kg (except MA3 : 85 kg) ;
- MTB rims :
- 75 kg on X517 ;
- 90 kg on X139, X139 Disc, X221, X223 Disc, X225, X 317 Disc,
X618, X3.1 and X3.1 Disc ;
- 115 kg on F219 Disc, F519, D521, D321 Disc and D3.1 Disc.
- Asphalt [touring] rims : 105 kg on T223 and T224, 125 kg on T520."

So the 275lb rider (that makes around 125kg or am I wrong?) could only
use the T520 rim in the Mavic Range.... and taking into account the
bike weight, he should go elsewhere.

I agree with this. While 37/85 is not a good combination with this rim,
it does not seem to be the only factor, the rider's 275lb weight being
even worse. Still, I would like to know why the plot above does not
give a horizontal line for Mavic's specs. Perhaps only the 25 and 28
specs are ideal, and for the rest they give a further safety factor.
This makes sense according to the tire/rim compatibility charts,
although I don't have time to check them right now.

Thus apart from any tire/rim incompatibility, the rim itself is clearly
way too underbuilt for the rider's weight. There may or may not also
have been a manufacturing defect, but there does not seem to be any
necessity for that.

Quoted message said:

Quoted message said:

I suggest the rider needs a 500+ g rim,

Sounds very sensible according to the above.

Problem may be finding a good one, especially if the rider doesn't want
to go the 600+g route. The Ambrosio Evolution, box section at 480g,
with 32mm tires, might be a bare safe minimum, but here someone of that
size should speak up and let us know. The concept of "bare safe
minimum" is a little unclear anyway.
e

Quoted message said:

Quoted message said:

That shows it : the 37mm@85psi configuration puts (a tad) less stress
on the rim walls than a Mavic-acceptable (and quite common)
23mm@138psi.

That's exactly what I thought, without looking at any specs in fact (if
you can, read my post on it in it.sport.cuclismo).
The stress on the rim from the inflated tube depends on the inflation
pressure and the width of the bed onto which the tube pushes. It has
nothin g to do with how large the tube and tire are outside of the rim.

At least, this is what makes sense to me.

Correct, but there is also force in the other direction, on the
hooks/wall, which depends on the product of inflation pressure and tire
cross sectional radius.

Quoted message said:

Add a rider who weighs twice as much as you do, and 500 miles later
the rim fails dramatically, just as expected.

Darned few riders weighing 265 lbs are likely to be putting 37mm tires
at 80-85 psi on such a narrow rim. The ones who do are going to find
out the hard way that it's a very bad idea.

The posters who are surprised are generally riding 35mm or smaller
tires (that 2mmm matters), using 75% or less as much pressure (20 to
40 psi makes a big difference down that low), and don't weigh 265 lbs
(60 to 130 pounds less is a considerable change).

Carl,

You've posted about the rider's weight several times in this thread, and
I don't understand the attention you're giving his weight. Why do you
think the rider weight is so important? ISTM rider weight won't change
the tube pressure or hoop stress significantly.

Pat

41 said:

Correct, but there is also force in the other direction, on the
hooks/wall, which depends on the product of inflation pressure and tire
cross sectional radius.

I beg to differ, here.
Strictly speaking there is a continuum of angles, and trigonometric
factors, involved; the result of all being just the (weighted)
vectorial sum. There is no way any such contribution can depend on
anything but the inside pressure, no matter what the shape of the other
portions of the tube are, which does depend on the size of the
clincher.
So, what ultimately matters is only the shape of the rim, to which that
portion of the tube conforms, and the inflation pressure.

Sergio
Pisa

Quoted message said:

41 said:

If we plot hoop force per unit length as caculated by a previous poster
as P*R, versus tire size, the results are not a horizontal line. The
figures (force in megaN) are:

mm psi MN/m
19 146 9.56 (spec)
23 138 10.94 (spec)
25 131 11.29 (spec)
28 117 11.29 (spec)
35 88 10.62 (spec)
37 85 10.84 (catastrophic failure)

That shows it : the 37mm@85psi configuration puts (a tad) less stress
on the rim walls than a Mavic-acceptable (and quite common)
23mm@138psi.
So, this configuration alone cannot be a single cause for the failure,
but the high-side load generated may be a contributive factor.

On the other hand, rider weight can also be a factor according to
Mavic's documentation. I can not find it again on Mavic's website, but
I found the following downloaded 2-3 years ago (original in french, I
tried to translate) :

"Mavic recommends that the total weight of the biker and his gear does
not exceeds the following :
- Road rims : 100 kg (except MA3 : 85 kg) ;
- MTB rims :
- 75 kg on X517 ;
- 90 kg on X139, X139 Disc, X221, X223 Disc, X225, X 317 Disc,
X618,

Damn, I have to get down to 90kg.

Greg

--
"All my time I spent in heaven
Revelries of dance and wine
Waking to the sound of laughter
Up I'd rise and kiss the sky" - The Mekons

41 wrote:
<snip>

Quoted message said:

Still, I would like to know why the plot above does not
give a horizontal line for Mavic's specs. Perhaps only the 25 and 28
specs are ideal, and for the rest they give a further safety factor.
This makes sense according to the tire/rim compatibility charts,
although I don't have time to check them right now.

<snip>

One factor no one has mentioned (at least not that I noticed) is that
the hoop stress we've calculated acts tangentially to the tire casing.
At the bead/rim interface, the diameter of the tire changes the
tangential direction substantially. For a given rim width (let's use
the Mavic rim in question) a 19mm tire's casing exerts force nearly
radially where it touches the rim. A 37mm tire exerts its force both
radially and axially (that is, in a direction parallel to the hub
axle). This axial force stresses the bead flange in bending. Of course,
the 19mm tire produces bending stresses in the rim's bead flange as
well, but those stresses are not nearly as high.

One data point:
I remember when Bontrager first re-sized MA40s and MA-2s...they were
shockingly light for mountain bike rims. People ran 2.2-inch tires on
those rims at maybe 55 psi. Trek briefly used their Matrix ISO-C
extrusion (a road aero rim) to make mountain bike rims. (This was prior
to Trek's purchase of Bontrager). That rim was quite narrow, and I had
a friend who ran 2.2-inch Gary Fisher tires (the plain square-block
ones) on those rims, and while they looked absurd on such narrow rims,
they worked fairly well for him. In retrospect it strikes me funny that
back in the day my friend was riding Bontrager-inspired Trek rims with
Fisher tires (on a Fisher Hoo Koo E Koo bike), and just a few years
later all three brands would be melded into a single entity. I guess it
shows how much the industry has consolidated.

At any rate, I'm not trying to suggest that tire width is irrelevant
because my skinny friend rode fat tires on skinny rims fifteen years
ago. I think tire width does matter, but so do a lot of other factors.

As much as I love computing stresses, I don't think that's the whole
story here. People have advanced all sorts of ornate theories about
this failure, but it's hard to know anything without a phyisical
inspection (and the photomicrographs that would result). It's certainly
an interesting topic for discussion, however.

Cheers,

Jason

Pat Lamb said:

Quoted message said:

Add a rider who weighs twice as much as you do, and 500 miles later
the rim fails dramatically, just as expected.

Darned few riders weighing 265 lbs are likely to be putting 37mm tires
at 80-85 psi on such a narrow rim. The ones who do are going to find
out the hard way that it's a very bad idea.

The posters who are surprised are generally riding 35mm or smaller
tires (that 2mmm matters), using 75% or less as much pressure (20 to
40 psi makes a big difference down that low), and don't weigh 265 lbs
(60 to 130 pounds less is a considerable change).

Carl,

You've posted about the rider's weight several times in this thread, and
I don't understand the attention you're giving his weight. Why do you
think the rider weight is so important? ISTM rider weight won't change
the tube pressure or hoop stress significantly.

Pat

Dear Pat,

No, the rider weight shouldn't change air pressure or the force that
the air pressure exerts on the side of the rim.

But the rider's weight constantly flexes the rim as it rolls under the
hub. In this case, when the spokes under the hub lose about 150 pounds
of tension, it's because that rim section is being pressed toward the
hub with 150 pounds of force. This force is exterted through the tire
sidewalls, which act partly like a wedge--some of the force goes to
spreading the rim.

With the pre-stressed aluminum rim, the flexing is invisible to the
naked eye, but the results in this case are not.

The heavier the rider, the greater the flexing, the sooner things
break.

Here's an imaginary metal bridge resembling the short section of rim
at the contact patch--which will break it sooner, a 180 pound weight
added and removed once per second, or a 275 pound weight added and
removed once per second?

Consider two more points.

Much heavier rims are routinely recommended for tandems that carry
about 275~350 pound loads. (Compare a truck rim to a car rim.)

The same rim with the same tire at the same inflation spinning in a
truing stand is unlikely to fail before the next ice age--no
fluctuation in stress in the rim.

But this rim failed in 500 miles, about 30 hours at 15~20 mph and
about 375,000 revolutions at about 750 revs per mile. Sounds like a
fatigue failure.

Cheers,

Carl Fogel

Quoted message said:

41 said:

ss
section. Compare the cross sections at
<www.ambrosiospa.com/cerchi_corsa.htm>, and you will see that their
comparable model, the Balance, is 500g, and it already has much thinner
walls than the 460g Excellence or the 480g Evolution, in turn both
thicker than the 430g Excellight.

Has anyone ever given a thought that a rim is under very severe stress
upon braking, which does not necessarily go with the rider's weight,
and that a thin wall and a non-boxed geometry are really bad features
in that regard?

Sergio
Pisa

Dear Sergio,

The frictional force retarding the spin is applied by rubber brake
pads, which should fail long before the aluminum rim--the rim sidewall
is coming at the pads lengthwise, giving it enormous strength that
way.

As for the pinching force at right angles, the rim is supported by
about 100 psi of air pressure--you have to squeeze that much just to
overcome the static pre-tension of the inner tube pushing the rim
outward.

Cheers,

Carl Fogel