mavic rims don't *all* suck

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dvt

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Feb 26, 2004, 12:54:51 PM2/26/04
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First, thanks a bunch to Carl Fogel for hosting the pictures and helping
me with formatting this message. I have documented a rim failure much
like one of those mentioned in the "mavic rims suck?" thread. This rim
served for a long time without trouble except the time I stacked it into
a snowbank off the side of a hairpin on a descent. I rebuilt the wheel
after that incident and it continued to serve well for a few more years.

Here are 8 *.jpg images of that rim after it failed. The links are
listed here for quick reference and also repeated in the text.

1. http://home.comcast.net/~carlfogel/download/rim_wide.JPG (135k)
2. http://home.comcast.net/~carlfogel/download/rim_label.JPG ( 40k)
3. http://home.comcast.net/~carlfogel/download/big_crack.JPG (111k)
4. http://home.comcast.net/~carlfogel/download/small_crack.JPG ( 86k)
5. http://home.comcast.net/~carlfogel/download/blowup_02.8_1.JPG ( 20k)
6. http://home.comcast.net/~carlfogel/download/blowup_02.8_2.JPG ( 46k)
7. http://home.comcast.net/~carlfogel/download/blowup_4_1.JPG ( 54k)
8. http://home.comcast.net/~carlfogel/download/blowup_4_2.JPG ( 52k)

This Mavic Open SUP CD rim from 1993 failed after 10's of thousands of
miles. It failed in 2003 while I was not on the bike. I inflated the
tires in the morning, rode to work, then found the rim in this condition
when I was ready to ride home at the end of the day. The failure was a
crack in the sidewall. I have no complaints, as the rim served a long
and useful life.

++++
Photo 1: Wide view of rim, with failures at approx 11 and 12 o'clock.
http://home.comcast.net/~carlfogel/download/rim_wide.JPG
++++
Photo 2: Label of the rim showing "Open SUP CD" at the top of the orange
label. This label is at about 8 o'clock on the previous picture.
http://home.comcast.net/~carlfogel/download/rim_label.JPG
++++

The failures were in the sidewall. I had originally presumed that
they were caused by brake wall wear. But after having read some of
the chatter on rec.bicycles.tech, I'm not sure anymore. Could this
be an anodizing failure? Here are some closeup photos of the failures
to help us decide.

++++
Photo 3: This is the larger failure seen at 11 o'clock in photo 1.
http://home.comcast.net/~carlfogel/download/big_crack.JPG
++++
Photo 4: This is the smaller failure seen at 12 o'clock in photo 1.
http://home.comcast.net/~carlfogel/download/small_crack.JPG
++++

Notice the white powder around the spoke socket in the photo 4.
Apparently the anodizing didn't prevent galvanic corrosion. The
yellowish stuff is adhesive residue from the rim strips.

Also note that both cracks are approximately centered on a spoke hole.
The rim should bulge a little bit at each spoke hole, causing the brake
wall to wear a little bit thinner in that area. Both of these failures
were on the right side of a wheel, and the spoke holes nearest the
failures contained spokes that pulled to the right. But the wheel was
a Shimano 8-speed rear, so the bracing angle was low and the bulge was
no longer noticable. Any bulge that had existed was rubbed out by brake
pad wear. The bulge on the left side spokes are still noticeable.

Now let's get even closer.

++++
Photo 5: A blown-up view of the photo 3. This side of the crack is
closest to the spoke bed. Bottom of photo is toward the spokes, top
of photo is the braking surface.
http://home.comcast.net/~carlfogel/download/blowup_02.8_1.JPG
++++
Photo 6: A blow-up of a different part of photo 3. Again, we see the
side closest to the spoke bed. You can see a bit of the socket in the
lower part of the picture. Bottom of photo is toward the spokes, top
of photo is the braking surface.
http://home.comcast.net/~carlfogel/download/blowup_02.8_2.JPG
++++
Photo 7: More magnification of a section from Photo 5. Bottom of photo
is toward the spokes, top of photo is the braking surface.
http://home.comcast.net/~carlfogel/download/blowup_4_1.JPG
++++
Photo 8: More magnification of a section from Photo 6. Bottom of photo
is toward the spokes, top of photo is the braking surface.
http://home.comcast.net/~carlfogel/download/blowup_4_2.JPG
++++

I don't know how to analyze the last four photos. I see that the shiny
part on the top half of the photos has striations perpendicular to the
thickness of the brake wall. I think that shiny part probably broke all
at once while the bike was parked.

I think the dull, rough section in the lower part of each photo came
apart slowly. But it isn't smooth with the parallel lines that typical
of a fatigue failure.

So what was the failure mode of this rim?

--
Dave
d...@psu.edu

Tom Nakashima

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Feb 26, 2004, 1:26:04 PM2/26/04
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Very interesting Dave, great photos by you and Carl...
never seen that failure in a rim before.
Might want to email these to Mavic, see what they say.
-tom

"dvt" <dvt_...@psu.edu> wrote in message
news:c1lbtc$du4$1...@f04n12.cac.psu.edu...

jobst....@stanfordalumni.org

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Feb 26, 2004, 1:46:32 PM2/26/04
to
Dave vt? writes:

> First, thanks a bunch to Carl Fogel for hosting the pictures and
> helping me with formatting this message. I have documented a rim
> failure much like one of those mentioned in the "mavic rims suck?"
> thread. This rim served for a long time without trouble except the
> time I stacked it into a snowbank off the side of a hairpin on a
> descent. I rebuilt the wheel after that incident and it continued to
> serve well for a few more years.

> Here are 8 *.jpg images of that rim after it failed. The links are
> listed here for quick reference and also repeated in the text.

> This Mavic Open SUP CD rim from 1993 failed after 10's of thousands
> of miles. It failed in 2003 while I was not on the bike. I inflated
> the tires in the morning, rode to work, then found the rim in this
> condition when I was ready to ride home at the end of the day. The
> failure was a crack in the sidewall. I have no complaints, as the
> rim served a long and useful life.

That is not what I would find acceptable. How would you feel if you
were descending a mountain road while the rim fell apart? Make that a
right hand turn with opposing traffic or at the entry of a hairpin turn
over an abyss. The rim shows no excessive wear on the braking surface
so it appeared to have plenty of life left... but it didn't.

> So what was the failure mode of this rim?

Cracking is a fatigue failure. The rough fracture (formerly called
"it crystallized") is a typical fatigue fracture. A forced rupture is
smoother and bright, it having occurred all at once from overload.

There is no reason to be an apologist for reckless manufacturing.
Anodizing is not to our advantage! But thanks for documenting that it
is so.

Jobst Brandt
jobst....@stanfordalumni.org

jobst....@stanfordalumni.org

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Feb 26, 2004, 1:56:24 PM2/26/04
to
Tom Nakashima writes:

> Very interesting Dave, great photos by you and Carl... never seen
> that failure in a rim before. Might want to email these to Mavic,
> see what they say.

That's old hat and they've seen it aplenty. As I said, bicycle shops
around here had rims where the rim cracked all the way around into the
hollow section, leaving the tire on the outer half and the spokes on
the inner, the wheel still slightly ridable. That was when the MA-40
came on the scene.

Jobst Brandt
jobst....@stanfordalumni.org

Tad Borek

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Feb 26, 2004, 3:00:37 PM2/26/04
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jobst....@stanfordalumni.org wrote:

> Dave vt? writes:
>>So what was the failure mode of this rim?
>
> Cracking is a fatigue failure. The rough fracture (formerly called
> "it crystallized") is a typical fatigue fracture. A forced rupture is
> smoother and bright, it having occurred all at once from overload.

Do you know where the motion comes from that leads to this type of
fatigue failure? Is it sidewall bending in response to, say, hard bumps
that momentarily increase the pressure in the tube? Is there a normal
cycle of sidewall bending that occurs as the wheel rotates? Is it
repetitions of inflating & deflating the tire/tube over a long time
period (akin to those old aluminum failures in aircraft, from
pressurization cycles)?

It seems some of this motion must be negligible - I'm wondering if
there's something in particular that is the biggest contributor to this
type of fatigue failure. Eg maybe there's an argument for keeping your
tires topped off even if you're not riding.

A curious thing is that it looks like two unconnected sections failed at
the same time. It makes sense to have a fracture that creeps in both
directions, even unzipping all the way around the rim, but unless I'm
seeing wrong it seems the cracks aren't connected. Viewing fatigue
failure ITO probabilities, it seems unlikely two unconnected sections
would reach the failure point on exactly the same day, after all those
years, especially because once it began to fail the pressure of the bead
must have dropped a bit (hypothesis: crack one began to propogate at
lower pressure than crack two, unless they began at the same time.
Yes/no?). So what was the trigger...a way-worn brake pad, dragging metal
on that edge? Higher than normal tire pressure that day? OP - after the
snowbank crash did you bend out the rim in these spots?

-Tad

dvt

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Feb 26, 2004, 3:39:19 PM2/26/04
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Tad Borek wrote:
> A curious thing is that it looks like two unconnected sections failed at
> the same time. It makes sense to have a fracture that creeps in both
> directions, even unzipping all the way around the rim, but unless I'm
> seeing wrong it seems the cracks aren't connected.

The fracture is not connected. I also found that odd for all the same
reaons you mention. I should have mentioned it in the OP.

> Viewing fatigue
> failure ITO probabilities, it seems unlikely two unconnected sections
> would reach the failure point on exactly the same day, after all those
> years, especially because once it began to fail the pressure of the bead
> must have dropped a bit (hypothesis: crack one began to propogate at
> lower pressure than crack two, unless they began at the same time.
> Yes/no?).

I don't know if they began at the same time. I didn't notice the crack
inceptions, only the final failure.

> So what was the trigger...a way-worn brake pad, dragging metal
> on that edge?

No grooves in the brake wall to indicate that. No noticeable marks on
the inside or the outside of the brake wall. Maybe I'll get pix of that.

> Higher than normal tire pressure that day?

I guess it was a bit higher than "normal" since I don't pump my tires up
frequently. I usually go weeks between inflations. I get slightly bigger
tires than I need to allow this laziness to occur.

> OP - after the
> snowbank crash did you bend out the rim in these spots?

No, I just released all spoke tension and started anew. When I had
removed all tension I laid the rim on a flat surface. The rim was still
flat.

Dave
dvt at psu dot edu

dvt

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Feb 26, 2004, 3:47:48 PM2/26/04
to
jobst....@stanfordalumni.org wrote:
>>This Mavic Open SUP CD rim from 1993 failed after 10's of thousands
>>of miles. It failed in 2003 while I was not on the bike. I inflated
>>the tires in the morning, rode to work, then found the rim in this
>>condition when I was ready to ride home at the end of the day. The
>>failure was a crack in the sidewall. I have no complaints, as the
>>rim served a long and useful life.

> That is not what I would find acceptable. How would you feel if you
> were descending a mountain road while the rim fell apart? Make that a
> right hand turn with opposing traffic or at the entry of a hairpin turn
> over an abyss. The rim shows no excessive wear on the braking surface
> so it appeared to have plenty of life left... but it didn't.

The braking surface is definitely concave. The braking surface *did*
show significant wear. I don't know if it was excessive. How thin does a
wall need to be in good aluminum? I don't know how thick the wall was
when the rim was new, so I can't comment on the change in thicknes. I
could measure the remaining wall thickness.

In retrospect, riding this rim in that well-worn condition was probably
not wise. But then we wouldn't be having all of this fun. :)

>>So what was the failure mode of this rim?

> Cracking is a fatigue failure. The rough fracture (formerly called
> "it crystallized") is a typical fatigue fracture. A forced rupture is
> smoother and bright, it having occurred all at once from overload.

There is part of the surface that appears to be forced rupture, as you
would expect when the crack propogated until the remaining wall was too
weak. The recent inflation was probably the proverbial last straw,
causing the rupture.

> There is no reason to be an apologist for reckless manufacturing.
> Anodizing is not to our advantage! But thanks for documenting that it
> is so.

Even if, as you say, the rough surface indicates fatigue, how does this
condemn the anodizing? How do I know this wouldn't have happened with an
MA-2 under the same conditions.

I currently have a pair of MA-2s on my commuter bike. Maybe I'll report
back in a few years with their failure mechanism. <g>

dianne_1234

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Feb 26, 2004, 5:50:31 PM2/26/04
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On Thu, 26 Feb 2004 20:00:37 GMT, Tad Borek <bor...@pacbell.net>
wrote:

>Do you know where the motion comes from that leads to this type of
>fatigue failure?

In theory, all causes "count". (Miner's rule, etc.)

> Is it sidewall bending in response to, say, hard bumps
>that momentarily increase the pressure in the tube?

The number of cycles of bump-hitting is normally many, many times less
than from just rolling. I'd neglect them.

> Is there a normal
>cycle of sidewall bending that occurs as the wheel rotates?

This is my guess as to the largest number of cycles. The bulge at the
bottom of the tire changes the angle at which the casing pulls on the
rim. This changes the bending moment. This is cyclic with every wheel
rotation.

> Is it
>repetitions of inflating & deflating the tire/tube over a long time
>period (akin to those old aluminum failures in aircraft, from
>pressurization cycles)?

Probably (Miner's rule again). My guess is there are far fewer cycles
of pumping than of rolling.

>It seems some of this motion must be negligible - I'm wondering if
>there's something in particular that is the biggest contributor to this
>type of fatigue failure. Eg maybe there's an argument for keeping your
>tires topped off even if you're not riding.

See above, by far the largest number of cycles comes from rolling.

Later the OP mentions larger tires. The casing of larger tires makes a
more horizontal angle with the rim, so increases the bending moment on
the rim side wall.

>A curious thing is that it looks like two unconnected sections failed at
>the same time.

Yeah, I thought so too! What are the chances of that? Never mind -- it
happened this once at least! :-)

jobst....@stanfordalumni.org

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Feb 26, 2004, 6:16:55 PM2/26/04
to
Tad Borek writes:

>>> So what was the failure mode of this rim?

>> Cracking is a fatigue failure. The rough fracture (formerly called
>> "it crystallized") is a typical fatigue fracture. A forced rupture
>> is smoother and bright, it having occurred all at once from
>> overload.

> Do you know where the motion comes from that leads to this type of
> fatigue failure? Is it sidewall bending in response to, say, hard
> bumps that momentarily increase the pressure in the tube? Is there a
> normal cycle of sidewall bending that occurs as the wheel rotates?
> Is it repetitions of inflating & deflating the tire/tube over a long
> time period (akin to those old aluminum failures in aircraft, from
> pressurization cycles)?

I think the FAQ item explains that. There is a large cycling lateral
load with each pass of the load affected zone:

http://draco.acs.uci.edu/rbfaq/FAQ/8b.25.html

> It seems some of this motion must be negligible - I'm wondering if
> there's something in particular that is the biggest contributor to
> this type of fatigue failure. Eg maybe there's an argument for
> keeping your tires topped off even if you're not riding.

This is for most rims an insignificant load unless there are crack
initiators. As I have mentioned, I have ridden MA-2 rims until
sidewalls were worn down to 0.5mm (0.020") with no failure.

> A curious thing is that it looks like two unconnected sections
> failed at the same time. It makes sense to have a fracture that
> creeps in both directions, even unzipping all the way around the
> rim, but unless I'm seeing wrong it seems the cracks aren't
> connected. Viewing fatigue failure ITO probabilities, it seems
> unlikely two unconnected sections would reach the failure point on
> exactly the same day, after all those years, especially because once
> it began to fail the pressure of the bead must have dropped a bit

> (hypothesis: crack one began to propagate at lower pressure than


> crack two, unless they began at the same time. Yes/no?). So what

> was the trigger... a way-worn brake pad, dragging metal on that


> edge? Higher than normal tire pressure that day? OP - after the
> snowbank crash did you bend out the rim in these spots?

I believe the cracks opened before parking the bicycle and that they
slowly peeled apart. I have observed this sort of failure somewhere
but I don't recall the circumstance.

Jobst Brandt
jobst....@stanfordalumni.org

jim beam

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Feb 26, 2004, 11:26:11 PM2/26/04
to
i think you're right, the rim served a long & useful life, especially as
a brake track, /by definition/, is subject to wear and is going to fail
in this way at some point, if other failure modes don't get to it first.

why did it crack when not in actual use? well, i'm becoming more & more
inclined to think there's a stress corrosion element to this picture.
the granular fracture surfaces in your pics are typical of such a
failure mode.

a micrograph showing this in more detail is here:
http://corrosion.ksc.nasa.gov/images/scc4.jpg

here, the crack can clearly be seen growing between the grains, not
progressing through them as is typical of fatigue.

your pics are not perfect, and may well show an element of fatigue under
closer examination, but the bright crystalline intergranular nature of
the bulk of the fracture surface is clear. it's not uncommon for
failures to combine stress corrosion, corrosion and fatigue, so it could
easily be a combination.

further examples of stress corrosion can be seen here:
http://technology.open.ac.uk/materials/mem/mem-corr.html

Werehatrack

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Feb 27, 2004, 1:26:59 AM2/27/04
to
On Thu, 26 Feb 2004 12:54:51 -0500, dvt <dvt_...@psu.edu> may have
said:

>First, thanks a bunch to Carl Fogel for hosting the pictures and helping
>me with formatting this message. I have documented a rim failure much
>like one of those mentioned in the "mavic rims suck?" thread. This rim
>served for a long time without trouble except the time I stacked it into
>a snowbank off the side of a hairpin on a descent. I rebuilt the wheel
>after that incident and it continued to serve well for a few more years.
>
>Here are 8 *.jpg images of that rim after it failed. The links are
>listed here for quick reference and also repeated in the text.
>
>1. http://home.comcast.net/~carlfogel/download/rim_wide.JPG (135k)
>2. http://home.comcast.net/~carlfogel/download/rim_label.JPG ( 40k)
>3. http://home.comcast.net/~carlfogel/download/big_crack.JPG (111k)
>4. http://home.comcast.net/~carlfogel/download/small_crack.JPG ( 86k)
>5. http://home.comcast.net/~carlfogel/download/blowup_02.8_1.JPG ( 20k)
>6. http://home.comcast.net/~carlfogel/download/blowup_02.8_2.JPG ( 46k)
>7. http://home.comcast.net/~carlfogel/download/blowup_4_1.JPG ( 54k)
>8. http://home.comcast.net/~carlfogel/download/blowup_4_2.JPG ( 52k)

Looking at the photos, I'd say that this was a fatigue failure due to
the way the fractured surface does not show a clean break. Fatigue
failures, in my experience, often indicate an understimate of the
loading that the item would receive (this often results in the
manufacturer saying that the item was *over*loaded, even though the
real problem may have been that they failed to take the probable
real-world in-service stresses into account properly). Without a
cross-section to look at, I have to wonder if they might not have
allowed too small of a fillet, or even created what amounted to a
sharp corner at the base of that flange. Sharp internal corners tend
to become failure points, and the break is typical of a sharp-corner
fatigue failure in my opinion.

Despite the long period in service, I have to say that I'm not
impressed. The rim's outer surface does not show the kind of brake
wear that would have made this less of a design concern and more of a
maintenance and inspection matter.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

Werehatrack

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Feb 27, 2004, 1:46:29 AM2/27/04
to
On Thu, 26 Feb 2004 15:39:19 -0500, dvt <dvt_...@psu.edu> may have
said:

>Tad Borek wrote:
>> So what was the trigger...a way-worn brake pad, dragging metal
>> on that edge?

>> Higher than normal tire pressure that day?
>
>I guess it was a bit higher than "normal" since I don't pump my tires up
>frequently. I usually go weeks between inflations. I get slightly bigger
>tires than I need to allow this laziness to occur.

This makes me think that the cracks had been present for a while, but
had not migrated all of the way through the flange, and only became
complete when the pressure provided the force to finally push the
broken sections out. Have you inspected the flanges on the *inside*
for signs of cracks around the rest of the circumference of the wheel?
I'm betting that you'll find that you have more than just the two
which precipitated the failures.

dvt

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Feb 27, 2004, 4:46:21 PM2/27/04
to
Werehatrack wrote:
> Have you inspected the flanges on the *inside*
> for signs of cracks around the rest of the circumference of the wheel?
> I'm betting that you'll find that you have more than just the two
> which precipitated the failures.

I don't see any cracks. The inside of the flanges is pretty gooped up
with Velox adhesive, so the cracks may be disguised.

--

dvt

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Feb 27, 2004, 4:51:15 PM2/27/04
to
dianne_1234 wrote:
> Later the OP mentions larger tires.

I should have quantified: 20-25 mm tires for the first part of the rim's
life, but in later years, I usually ran 28mm on those rims. I had 28mm
tires on at the time of failure (old Avocet Duro).

dvt

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Feb 27, 2004, 4:54:22 PM2/27/04
to
jobst....@stanfordalumni.org wrote:
> This is for most rims an insignificant load unless there are crack
> initiators. As I have mentioned, I have ridden MA-2 rims until
> sidewalls were worn down to 0.5mm (0.020") with no failure.

These sidewalls are ~1.5-1.8 mm thick at the crack.

How do you know when to replace a rim? Concavity in the brake wall? Do
you measure the wall thickness? Based on your earlier post, I don't
think you wait until they crack.

dvt

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Feb 27, 2004, 5:02:22 PM2/27/04
to
jim beam wrote:
> why did it crack when not in actual use? well, i'm becoming more & more
> inclined to think there's a stress corrosion element to this picture.
> the granular fracture surfaces in your pics are typical of such a
> failure mode.
>
> a micrograph showing this in more detail is here:
> http://corrosion.ksc.nasa.gov/images/scc4.jpg

I don't know what that picture represents. What's the scale? Is it
aluminum? What do the colors represent? I expect a micrograph is not
optical, so the colors probably represent the reflection of some sort of
beam other than visible wavelengths.

> your pics are not perfect, and may well show an element of fatigue under
> closer examination, but the bright crystalline intergranular nature of
> the bulk of the fracture surface is clear. it's not uncommon for
> failures to combine stress corrosion, corrosion and fatigue, so it could
> easily be a combination.

Suggestions for better pics? More magnification, diffuse light
source,....? I have access to a digital camera, optical microscopes that
range from 8-40x, and some garden-variety light sources. That's what I
used for these pictures.

dvt

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Feb 27, 2004, 5:06:18 PM2/27/04
to
Werehatrack wrote:

> Without a
> cross-section to look at, I have to wonder if they might not have
> allowed too small of a fillet, or even created what amounted to a
> sharp corner at the base of that flange. Sharp internal corners tend
> to become failure points, and the break is typical of a sharp-corner
> fatigue failure in my opinion.

The inside of the brake wall is pretty gradually curved. There are no
sharp points near the crack.

> Despite the long period in service, I have to say that I'm not
> impressed. The rim's outer surface does not show the kind of brake
> wear that would have made this less of a design concern and more of a
> maintenance and inspection matter.

Same question to you: How do you tell when a brake wall is too thin for
continued service?

Mike Latondresse

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Feb 27, 2004, 5:27:32 PM2/27/04
to
dvt <dvt_...@psu.edu> wrote in
news:c1of0q$1mom$2...@f04n12.cac.psu.edu:

>
> Same question to you: How do you tell when a brake wall is too
> thin for continued service?
>

When your brake lever begins to pulse as you apply them...and then the
end is close, real close.

SMMB

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Feb 27, 2004, 6:01:28 PM2/27/04
to

"dvt" <dvt_...@psu.edu> a écrit dans le message de :
news:c1of0q$1mom$2...@f04n12.cac.psu.edu...

> Werehatrack wrote:
> > Despite the long period in service, I have to say that I'm not
> > impressed..............


> Same question to you: How do you tell when a brake wall is too thin for
> continued service?
>

I think all the Mavic haters really believe that a virtuous rim gives its
soul to the hereafter, collapses into a pile of pixie-dust, having left a
note of regret.

Now that's the right failure mode ? Everything fails, somehow, sometime.
Same crowd, I would bet, that is wistful for the days of washable oil
filters for cars...
--
Bonne route,

Sandy
Paris FR


jim beam

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Feb 27, 2004, 7:58:27 PM2/27/04
to
dvt wrote:
> jim beam wrote:
>
>> why did it crack when not in actual use? well, i'm becoming more &
>> more inclined to think there's a stress corrosion element to this
>> picture. the granular fracture surfaces in your pics are typical of
>> such a failure mode.
>>
>> a micrograph showing this in more detail is here:
>> http://corrosion.ksc.nasa.gov/images/scc4.jpg
>
>
> I don't know what that picture represents. What's the scale? Is it
> aluminum? What do the colors represent? I expect a micrograph is not
> optical, so the colors probably represent the reflection of some sort of
> beam other than visible wavelengths.

the pic is a generic monochrome, taken with reflected light from an
optical metallurgical microscope after a sample has been sectioned and
polished. it's not to scale because it doesn't need to be - it simply
illustrates the nature of some stress corrosion cracking following along
grain boundary lines in the metal. [grains are individual metal
crystals just like individual cells in biological samples.]

this is relevant to your pics because they show a polycrystalline
fracture surface where the metal has separated at grain boundaries.

>
>> your pics are not perfect, and may well show an element of fatigue
>> under closer examination, but the bright crystalline intergranular
>> nature of the bulk of the fracture surface is clear. it's not
>> uncommon for failures to combine stress corrosion, corrosion and
>> fatigue, so it could easily be a combination.
>
>
> Suggestions for better pics? More magnification, diffuse light
> source,....? I have access to a digital camera, optical microscopes that
> range from 8-40x, and some garden-variety light sources. That's what I
> used for these pictures.
>

they need to be in focus! if you want to determine the extent of any
fatigue, you need to have the fracture surface in focus, particularly
that inside edge, which will require having the plane of the fracture
parallel to the optical focus plane. the ideal light source is
reflected from the objective lens itself - some biological microscopes
have this feature, but most use transmitted light so you'll have to do
the best you can with a source as close and as perpendicular as possible.

if the cracks initiated with fatigue from the inside of the rim, there
will be a comparatively smooth "beach mark" surface extending from that
inside edge into the wall thickness. you may need significantly more
magnification than 40x to detect this if the matreial has gone straight
from the slow growth region to brittle fracture, but have a go and see
what you can do.

jobst....@stanfordalumni.org

unread,
Feb 27, 2004, 8:41:16 PM2/27/04
to
Dave vt? writes:

>> This is for most rims an insignificant load unless there are crack
>> initiators. As I have mentioned, I have ridden MA-2 rims until
>> sidewalls were worn down to 0.5mm (0.020") with no failure.

> These sidewalls are ~1.5-1.8 mm thick at the crack.

> How do you know when to replace a rim? Concavity in the brake wall?
> Do you measure the wall thickness? Based on your earlier post, I
> don't think you wait until they crack.

I have a calibrated thumb and forefinger that I pass over the rim in a
brake caliper manner feeling the hollow cheeks of the rim. I know how
0.5mm wall feels. On a tour of the Alps on which it rained on almost
every major descent. I noticed at the top of the Stelvio that I was
at the limit on the front rim. Because it was raining, I could not
use the front brake, so I used only the rear brake to descend.
Afterwards, in the flatland, as soon as the road was dry, I could use
the front brake again, because practically no wear occurs when dry
with Kool-Stop Salmon red pads because they don't get grit inclusions.
I have a section of that and other rims, in my collection.

Jobst Brandt
jobst....@stanfordalumni.org

carlfogel

unread,
Feb 27, 2004, 10:10:42 PM2/27/04
to
Jobst Brandt wrote:
> Dave vt? writes:
> >> This is for most rims an insignificant load unless there are crack
> >> initiators. As I have mentioned, I have ridden MA-2 rims until
> >> sidewalls were worn down to 0.5mm (0.020") with no failure.
> > These sidewalls are ~1.5-1.8 mm thick at the crack.
> > How do you know when to replace a rim? Concavity in the brake wall? Do
> > you measure the wall thickness? Based on your earlier post, I don't
> > think you wait until they crack.
> I have a calibrated thumb and forefinger that I pass over the rim in a
> brake caliper manner feeling the hollow cheeks of the rim. I know how
> .5mm wall feels. On a tour of the Alps on which it rained on almost
> every major descent. I noticed at the top of the Stelvio that I was at
> the limit on the front rim. Because it was raining, I could not use the
> front brake, so I used only the rear brake to descend. Afterwards, in
> the flatland, as soon as the road was dry, I could use the front brake
> again, because practically no wear occurs when dry with Kool-Stop Salmon
> red pads because they don't get grit inclusions. I have a section of
> that and other rims, in my collection.
> Jobst Brandt jobst....@stanfordalumni.org

Dear Jobst,

Hmm . . . it might have been safer to back down the Stelvio, like a
Model T taking advantage of its unworn reverse.

Analysis reveals unmistakable humor inclusions.

But don't quit your day job(st).

Thumbs up,

Carl Fogel

--


Werehatrack

unread,
Feb 28, 2004, 2:50:45 AM2/28/04
to

Aluminum rims appear not to have a "right" failure mode, but given
that the indestructible steel rims also had the distinct disadvantage
of being lousy as brake components, failure seems to be the lot we
must accept. What I don't see is why the brake surfaces of the rims
aren't made a bit thicker on some wheels (leaving, of course, some
with lighter weight for those whose preference is for lightness over
durability) with a marked and measurable wear limit in the same way
that such a specification is given for the brake discs on automobiles.

Werehatrack

unread,
Feb 28, 2004, 2:55:48 AM2/28/04
to
On Fri, 27 Feb 2004 16:46:21 -0500, dvt <dvt_...@psu.edu> may have
said:

>Werehatrack wrote:

That's quite possible. It's probably academic, though, since the rim
is obviously going to be out of service anyway. Even if there were
cracks that could have been found, it's unlikely that they would have
been spotted prior to the failure since it's not like you're going to
rip a good sew-up off of the wheel just to inspect the flanges
periodically.

Matt O'Toole

unread,
Feb 28, 2004, 12:02:00 PM2/28/04
to
Werehatrack wrote:

> Aluminum rims appear not to have a "right" failure mode,

What does this mean?

> but given
> that the indestructible steel rims also had the distinct disadvantage
> of being lousy as brake components, failure seems to be the lot we
> must accept. What I don't see is why the brake surfaces of the rims
> aren't made a bit thicker on some wheels (leaving, of course, some
> with lighter weight for those whose preference is for lightness over
> durability) with a marked and measurable wear limit in the same way
> that such a specification is given for the brake discs on automobiles.

This is exactly what we have. Some rims are thick (and heavier), some are light
(and thinner), and nowadays rims have wear indicators molded into the sidewalls
(as required by law in Europe, IIRC). Previously, one could determine wear by
measuring.

The whole point of this thread is that no matter how thick the sidewalls, rims
no longer last until the wear limit is reached -- they crack first.

Matt O.


jim beam

unread,
Feb 28, 2004, 3:23:11 PM2/28/04
to
Matt O'Toole wrote:
<snip

>
> The whole point of this thread is that no matter how thick the sidewalls, rims
> no longer last until the wear limit is reached -- they crack first.
>

is this a fact? what testing have you done? what were your controls?

Tim McNamara

unread,
Feb 28, 2004, 5:53:09 PM2/28/04
to
Werehatrack <rau...@earthWEEDSlink.net> writes:

> On Sat, 28 Feb 2004 00:01:28 +0100, "SMMB"
> <please.do...@free.fr> may have said:
>
>>Now that's the right failure mode ? Everything fails, somehow,
>>sometime.
>

> Aluminum rims appear not to have a "right" failure mode

The "right" failure mode is one that is predictable and
non-catastrophic. Non-anodized and socketed aluminum rims have the
right failure mode in that failure is predictable from braking area
wear. Anodized rims, introducing new catastrophic failure modes, do
not have the "right" failure mode.

Tim McNamara

unread,
Feb 28, 2004, 5:54:11 PM2/28/04
to
jim beam <u...@ftc.gov> writes:

You haven't been reading along, have you? Or are you just pretending
to be dense?

Carl Fogel

unread,
Feb 28, 2004, 5:59:24 PM2/28/04
to
"Matt O'Toole" <ma...@deltanet.com> wrote in message news:<cQ30c.6138$6K....@nwrddc02.gnilink.net>...

[snip worthy werehatrack brake-wear indicator suggestion]

>
> The whole point of this thread is that no matter how thick the sidewalls, rims
> no longer last until the wear limit is reached -- they crack first.
>
> Matt O.

Dear Matt,

You may need to explain what you mean. (Try to be patient
with everyone who jumps on you.)

Are you saying that you expect anodized rims to crack elsewhere
before the rims fail because of brake wear? (Cracks, for example,
around spoke holes, or cracks around the rim not related to
brake-worn areas. Are there such cracks in these pictures?)

Or do you expect anodized rims to crack in the brake area
before normal brake wear should ruin them? (Anodizing is
usually removed from brake areas, either by the machining
process or else by normal brake wear, but it might somehow
still be involved.)

Despite its title, this thread has no point. Dave just asked
us all to look at pictures of his failed rim and to try to
figure out why it failed. Is the culprit anodization, brake
wear, a combination of the two, or something else?

Personally, I think that an awful lot of questions need to be
asked about Dave's sons. The sudden failure of metal objects,
including anvils, is often noticed when children appear.

Carl Fogel

Mike S.

unread,
Feb 28, 2004, 7:12:18 PM2/28/04
to

"Tim McNamara" <tim...@bitstream.net> wrote in message
news:m2k726d...@Stella-Blue.local...

'scuse me again. Most of the cracks we've discussed here aren't
catastrophic in nature.

If I'm mistaken, please correct me. Eyelets coming thru the rims, cracks
radiating outward from the holes the eyelets sit in, etc. yes, but IIRC
there were only two cases of "whoops! My rims went bang!" and both of those
were older rims...

I don't remember if my RM20s were anodized or not. I had the sidewalls blow
out from being too thin. Appx a 6" section of brake track pulled away from
the rest of the rim. I could tell that they were on their last legs 'cause
the brake track was concave.

Being a broke college student, I figured I'd ride them till they broke
anyway.

Mike


jim beam

unread,
Feb 28, 2004, 9:46:19 PM2/28/04
to
ok tim, explain what i'm missing.

or are you just trying to pick a fight?

Matt O'Toole

unread,
Feb 28, 2004, 11:12:07 PM2/28/04
to
Carl Fogel wrote:

> Are you saying that you expect anodized rims to crack elsewhere
> before the rims fail because of brake wear? (Cracks, for example,
> around spoke holes, or cracks around the rim not related to
> brake-worn areas. Are there such cracks in these pictures?)
>
> Or do you expect anodized rims to crack in the brake area
> before normal brake wear should ruin them? (Anodizing is
> usually removed from brake areas, either by the machining
> process or else by normal brake wear, but it might somehow
> still be involved.)

I expect rims to not crack at all, and be serviceable until retired from brake
wear, or crashed. This has been covered ad infinitum -- if not in this
particular thread, then in the one it came from -- and in this newsgroup, for
over a decade.

> Despite its title, this thread has no point. Dave just asked
> us all to look at pictures of his failed rim and to try to
> figure out why it failed. Is the culprit anodization, brake
> wear, a combination of the two, or something else?

That's a fatigue failure, and the third picture makes me suspect the anodizing
played a part.

> Personally, I think that an awful lot of questions need to be
> asked about Dave's sons. The sudden failure of metal objects,
> including anvils, is often noticed when children appear.

Yes, but one could still determine whether said failure was due to fatigue.

Matt O.


Tim McNamara

unread,
Feb 29, 2004, 12:32:58 AM2/29/04
to
"Mike S." <mikeshaw2@coxDOTnet> writes:

> "Tim McNamara" <tim...@bitstream.net> wrote in message
> news:m2k726d...@Stella-Blue.local...
>
>> Werehatrack <rau...@earthWEEDSlink.net> writes:
>>
>> > On Sat, 28 Feb 2004 00:01:28 +0100, "SMMB"
>> > <please.do...@free.fr> may have said:
>> >
>> >>Now that's the right failure mode ? Everything fails, somehow,
>> >>sometime.
>> >
>> > Aluminum rims appear not to have a "right" failure mode
>>
>> The "right" failure mode is one that is predictable and
>> non-catastrophic. Non-anodized and socketed aluminum rims have the
>> right failure mode in that failure is predictable from braking area
>> wear. Anodized rims, introducing new catastrophic failure modes,
>> do not have the "right" failure mode.
>
> 'scuse me again. Most of the cracks we've discussed here aren't
> catastrophic in nature.

Because they were spotted in time.

> If I'm mistaken, please correct me. Eyelets coming thru the rims,
> cracks radiating outward from the holes the eyelets sit in,
> etc. yes, but IIRC there were only two cases of "whoops! My rims
> went bang!" and both of those were older rims...

Eyelets coming through the rim would be catastrophic failure, quite
possibly rendering the wheel instantly unrideable and potentially
causing the wheel to lock up. Not the best situation if you're riding
in heavy traffic or descending a mountain road at the time, or at any
time if it's the front wheel. Or if you're 60 miles into a 120 mile
ride. You've apparently missed the references to other catstrophic
rim failures that have been mentioned in connection to hard andized
rims in particular (not surprising given the stupendous length of this
thread; I've not read every post and skipped the ones about asphalt
almost entirely).

> I don't remember if my RM20s were anodized or not. I had the
> sidewalls blow out from being too thin. Appx a 6" section of brake
> track pulled away from the rest of the rim. I could tell that they
> were on their last legs 'cause the brake track was concave.

In which case you had advance warning- hence the "right" failure
mode.

> Being a broke college student, I figured I'd ride them till they
> broke anyway.

Not only broke but apparently having little regard for your own
safety.

carlfogel

unread,
Feb 29, 2004, 12:50:56 AM2/29/04
to

Dear Matt,

You wrote, "I expect rims to not crack at all, and be serviceable until


retired from brake wear, or crashed."

But Dave's point is that his rim may have gone past the point when it
should have been retired due to brake wear and may therefore have cracked--
he can't tell whether it's anodizing or just worn out.

How would the two kinds of cracks differ?

What is it about the third picture that makes you suspect that the
anodizing played a part?

That's what Dave is interested in. (Well, that and exonerating
his sons.)

Carl Fogel

--


jobst....@stanfordalumni.org

unread,
Feb 29, 2004, 1:07:00 AM2/29/04
to
Werehatrack <rau...@earthweedslink.net> writes:

>>> Have you inspected the flanges on the *inside*
>>> for signs of cracks around the rest of the circumference of the wheel?
>>> I'm betting that you'll find that you have more than just the two
>>> which precipitated the failures.

>> I don't see any cracks. The inside of the flanges is pretty gooped
>> up with Velox adhesive, so the cracks may be disguised.

> That's quite possible. It's probably academic, though, since the
> rim is obviously going to be out of service anyway. Even if there
> were cracks that could have been found, it's unlikely that they
> would have been spotted prior to the failure since it's not like
> you're going to rip a good sew-up off of the wheel just to inspect
> the flanges periodically.

As far as I could see, this is a clincher rim and the crack should be
detectable on the outside when it first developed. As was mentioned,
it grew and failed while parked, so it must have been there before it
was parked. In any case, with many years of no anodized rims, such
failures did not occur to any of the many bikies in our area. In
contrast, with the advent of dark anodized rims, they occurred often.

Jobst Brandt
jobst....@stanfordalumni.org

jobst....@stanfordalumni.org

unread,
Feb 29, 2004, 1:10:27 AM2/29/04
to
Matt O'Toole writes:

> What does this mean?

Oh Matt, you blaspheme. You seem to have sold your heart to the
technical opposition. The anodizing Mafia will get on your case.

Jobst Brandt
jobst....@stanfordalumni.org

jobst....@stanfordalumni.org

unread,
Feb 29, 2004, 1:20:25 AM2/29/04
to
Carl Fogel writes:

>> The whole point of this thread is that no matter how thick the
>> sidewalls, rims no longer last until the wear limit is reached --
>> they crack first.

> Dear Matt,

> You may need to explain what you mean. (Try to be patient
> with everyone who jumps on you.)

> Are you saying that you expect anodized rims to crack elsewhere
> before the rims fail because of brake wear? (Cracks, for example,
> around spoke holes, or cracks around the rim not related to
> brake-worn areas. Are there such cracks in these pictures?)

> Or do you expect anodized rims to crack in the brake area before
> normal brake wear should ruin them? (Anodizing is usually removed
> from brake areas, either by the machining process or else by normal
> brake wear, but it might somehow still be involved.)

The rim in question was not worn thin, certainly not thin enough to
fail from the experience I have with observing anodized rim failures
at local bicycle shops and among the riders with whom I have ridden.
The cross section of the failed subject rim is evident from the
separation photos that show at least 1mm thickness.

> Despite its title, this thread has no point. Dave just asked us all
> to look at pictures of his failed rim and to try to figure out why
> it failed. Is the culprit anodization, brake wear, a combination of
> the two, or something else?

He also made the claim in contrast to other postings that these rims
do not fail in a dange4ous manner. That is the bone of contention. I
brought that up and there is apparently no argument with my contention
that this is as dangerous a failure as one can encounter. To
visualize the danger one must either ride in traffic or descend
mountain roads that border precipices.

> Personally, I think that an awful lot of questions need to be
> asked about Dave's sons. The sudden failure of metal objects,
> including anvils, is often noticed when children appear.

Is this an attempt at humor or are you insinuating that Dave is blind
to hazards?

Jobst Brandt
jobst....@stanfordalumni.org

Qui si parla Campagnolo

unread,
Feb 29, 2004, 9:59:24 AM2/29/04
to
Jobst-<< I have a calibrated thumb and forefinger that I pass over the rim in a

brake caliper manner feeling the hollow cheeks of the rim. I know how
0.5mm wall feels. >><BR><BR>


heee, heee.....

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

Werehatrack

unread,
Feb 29, 2004, 12:02:00 PM2/29/04
to
On Sun, 29 Feb 2004 06:20:25 GMT, jobst....@stanfordalumni.org may
have said:

>Carl Fogel writes:

>> Personally, I think that an awful lot of questions need to be
>> asked about Dave's sons. The sudden failure of metal objects,
>> including anvils, is often noticed when children appear.
>
>Is this an attempt at humor or are you insinuating that Dave is blind
>to hazards?

I'm sure it was in jest. Merely mentioning anvils and children in the
same utterance is a strong indicator. (And here I was thinking that
you'd begun to grow a sense of humor...perhaps it just needs a bit
more cultivating, you've actually managed to be witty more than a few
times lately. Don't stop now!)

jim beam

unread,
Feb 29, 2004, 12:23:08 PM2/29/04
to
Matt O'Toole wrote:
> Carl Fogel wrote:
>
>
>>Are you saying that you expect anodized rims to crack elsewhere
>>before the rims fail because of brake wear? (Cracks, for example,
>>around spoke holes, or cracks around the rim not related to
>>brake-worn areas. Are there such cracks in these pictures?)
>>
>>Or do you expect anodized rims to crack in the brake area
>>before normal brake wear should ruin them? (Anodizing is
>>usually removed from brake areas, either by the machining
>>process or else by normal brake wear, but it might somehow
>>still be involved.)
>
>
> I expect rims to not crack at all, and be serviceable until retired from brake
> wear, or crashed. This has been covered ad infinitum -- if not in this
> particular thread, then in the one it came from -- and in this newsgroup, for
> over a decade.

be practical matt. when a rim has worn to its failure "thiness" it's
going to fail - there's nothing you can do to stop it other than arrest
the wear in the first place - that's what ceramic rims are for, but
again, thay get so roundly condemned on this forum by those that have
never used them, it makes it almost impossible to have rational debate.

in regard to "acceptable" failure modes, what would work for you? even
the cast iron brake disks on your car will crack when they get thin enough.

>
>
>>Despite its title, this thread has no point. Dave just asked
>>us all to look at pictures of his failed rim and to try to
>>figure out why it failed. Is the culprit anodization, brake
>>wear, a combination of the two, or something else?
>
>
> That's a fatigue failure, and the third picture makes me suspect the anodizing
> played a part.

with respect, there's nothing evident from those pics that allows a
definite conclusion of that nature - there's not enough resolution to
definitively confirm fatigue, nor any of the other possible failure
modes for that matter. the fracture surface is arguably intergranular,
which is /not/ typical of fatigue progression, but again, better
resolution is required to be sure. beyond that, it's guesswork &
conjecture.

>
>
>>Personally, I think that an awful lot of questions need to be
>>asked about Dave's sons. The sudden failure of metal objects,
>>including anvils, is often noticed when children appear.
>
>
> Yes, but one could still determine whether said failure was due to fatigue.

with proper analysis, yes, but with all due respect to the op's artwork,
there is nothing here that is sufficient for that conclusion.

>
> Matt O.
>
>

Werehatrack

unread,
Feb 29, 2004, 12:25:31 PM2/29/04
to
On Sun, 29 Feb 2004 05:50:56 GMT, carlfogel
<usenet...@cyclingforums.com> may have said:

>[Matt] wrote, "I expect rims to not crack at all, and be serviceable until


>retired from brake wear, or crashed."
>
>But Dave's point is that his rim may have gone past the point when it
>should have been retired due to brake wear and may therefore have cracked--
>he can't tell whether it's anodizing or just worn out.

As observed by Jobst Brandt, the wear present would not seem
sufficient to judge the rim past reasonable limits in that area. I
agree with his assessment based on the photos. As such, the rim's
failure seems premature.

>How would the two kinds of cracks differ?

I would expect a failure due to wear to be a shearing break, without
the granularity present in the photos; the granularity indicates a
crack which developed due to flexing or bending.

>What is it about the third picture that makes you suspect that the
>anodizing played a part?

I can't answer for anyone but myself, but I'd have to see some
different data before I could eliminate the possibility that the
anodization was a factor. From what's present, all *I* can say is
that it looks like a crack formed in a flange that did not have
excessive wear, that the crack looks to me like it began at the inner
surface and migrated outward, and that it appears that it was not due
to a sudden failure. This is consistent with, among other things, a
crack that followed a stress riser of the type that could have formed
due to etching of the metal during the anodizing process. I have
observed over the years that extrusions etched with acids sometimes
have a linear grain which can be brought out readily; the resulting
ridged/grooved surface creates many small stress risers. Such a
stress riser might take a long time to be revealed by a failure. I
can't say if that's the mechanism of failure for the wheel in
question, but I can't rule it out, and it's consistent with the
available data.

>That's what Dave is interested in. (Well, that and exonerating
>his sons.)

Unless his sons have an Acme catalog, I doubt that they're going to
have been involved. ("If it's not an ACME anvil, it's not funny!")

Werehatrack

unread,
Feb 29, 2004, 12:35:14 PM2/29/04
to
On Sun, 29 Feb 2004 06:07:00 GMT, jobst....@stanfordalumni.org may
have said:

>Werehatrack <rau...@earthweedslink.net> writes:
>
>>>> Have you inspected the flanges on the *inside*
>>>> for signs of cracks around the rest of the circumference of the wheel?
>>>> I'm betting that you'll find that you have more than just the two
>>>> which precipitated the failures.
>
>>> I don't see any cracks. The inside of the flanges is pretty gooped
>>> up with Velox adhesive, so the cracks may be disguised.
>
>> That's quite possible. It's probably academic, though, since the
>> rim is obviously going to be out of service anyway. Even if there
>> were cracks that could have been found, it's unlikely that they
>> would have been spotted prior to the failure since it's not like
>> you're going to rip a good sew-up off of the wheel just to inspect
>> the flanges periodically.
>
>As far as I could see, this is a clincher rim

Yes, correct; I must have been half asleep; I missed the "velox" and
just saw "adhesive". Still, I doubt that the average owner would
expect to need to be observant for this specific type of failure.
And, to make matters worse, would the dark anodizing not tend to make
such a crack harder to spot?

Werehatrack

unread,
Feb 29, 2004, 12:37:54 PM2/29/04
to
On Sat, 28 Feb 2004 01:41:16 GMT, jobst....@stanfordalumni.org may
have said:

>I have a calibrated thumb and forefinger that I pass over the rim in a
>brake caliper manner feeling the hollow cheeks of the rim. I know how
>0.5mm wall feels.

I my days of building performance engines, I used to joke about my
"eyecrometer"; with experience, organic tools can be amazingly
accurate.

jim beam

unread,
Feb 29, 2004, 12:43:56 PM2/29/04
to

you keep making this allegation jobst, but the only "evidence" i've ever
seen you present that "supports" your "anodizing induced fatigue" theory
is dye penetrant testing. all dye penetration does is tell you whether
there is a crack detectable by that means. it does *NOT* analyze cause.

you also make the [il]logical jump from the presence of a dye penetrant
positive to the complete diagnosis of its initiation, propagation &
eventual failure. you've never addressed the effects of alloy
composition, environment or even spoke tension on your analysis - you
merely assert that "it never used to happen before... so i therefore
conclude that... ". that's not complete analysis and certainly no
causal definition.

in the case of the above photos, which while they are too unfocused to
show conclusive evidence of anything, /do/ arguably show some
intergranular cracking features. intergranular cracking is /not/
typical of fatigue, whether it be anodizing induced or not.

in short, this is probably a complex failure. asserting guesswork
pertaining to only one particular potential failure element is
amateurish. you fail to differentiate between different anodizing
processes. what you probably are trying to say is that hard anodizing
induced cracking, but instead you use the term "dark" anodizing, which
is too broad a definition and includes cosmetic processing. normal
anodizing that has been dyed is no worse than clear anodizing - and
clear anodizing is not a problem as evidenced by the vast quantities of
clear anodized ma2's that were sold. failure to differentiate between
normal protective [and cosmetic] anodizing & hard anodizing merely
serves to undermine you.


>
> Jobst Brandt
> jobst....@stanfordalumni.org


Mike S.

unread,
Feb 29, 2004, 1:02:22 PM2/29/04
to

<jobst....@stanfordalumni.org> wrote in message
news:8kf0c.4505$_3.7...@typhoon.sonic.net...

Hey Jobst,

How many of those rims that never failed were actually clinchers? Yah, I
know you love MA2s, but the rest?

What were the percentage of people riding tubulars vs. clinchers?

Ya think that maybe, just maybe, that some sidewall failures may have
something to do with about a cm of unsupported metal being stressed by
holding together a clincher inflated to 110psi+?

Next question: what weight were those clincher rims that never failed?
400g, 500g?

Just curious... since I haven't been studying stuff like this for as long
as you have.

Mike


Carl Fogel

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Feb 29, 2004, 1:17:53 PM2/29/04
to
jobst....@stanfordalumni.org wrote in message news:<Jwf0c.4507$_3.7...@typhoon.sonic.net>...

Dear Jobst,

I have a hideous suspicion that I just accidentally
posted a list of potential questions as a reply to
your post.

I was working through the questions in another window,
eliminating most of them as foolish and the rest as
ill-natured, when the original vanished in a manner
that suggests that it escaped into the newsgroup.

If there is such a previous post, probably unsigned,
consider it a glimpse into raw workings of an unbalanced
mind and ignore it as you would the mutterings of
Tourette's syndrome.

Ruefully,

Carl Fogel

Carl Fogel

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Feb 29, 2004, 2:16:21 PM2/29/04
to
"Mike S." <mikeshaw2@coxDOTnet> wrote in message news:<B7a0c.19518$qL1.8973@fed1read02>...

[snip]

>
> I don't remember if my RM20s were anodized or not. I had the sidewalls blow
> out from being too thin. Appx a 6" section of brake track pulled away from
> the rest of the rim. I could tell that they were on their last legs 'cause
> the brake track was concave.
>
> Being a broke college student, I figured I'd ride them till they broke
> anyway.
>
> Mike

Dear Mike,

My 1994 Pedal Pusher BikePro catalogue has a two-page
rim table and lists Araya RM-20 rims in 24" and 26"
with oodles of details (eighteen columns).

Two kinds of surface treatment are listed for the Araya
RM-20 rims, Anodized (silver, clear) and Hard Anodized
(gray and other colors).

"Hard anodizing is the same electrical process performed
at a higher voltage in a different acid bath. It delivers
a thickening of the hardened surface layer to a greater
depth in the metal's surface. Hard anodizing is said to
increase a rim's rigidity between 10 and 20 per cent.
Somehow that seems a little high, but it certainly adds
something to a rim's weight, as the Rim Table demonstrates."

The table lists the 36-hole Araya RM-20 26" rim as weighing
509 grams after clear-silver anodizing, 533 grams after
gray-hard anodizing. Oxidation is fattening.

About fifty rims are listed in the table on two small-print
pages, and there are eight three-column pages of detailed
comments on the manufacturing process, with pictures of each
rim's cross-section, label, and spoke-bed.

Interestingly, the detail on the Mavic Open SUP CD hard
anodized finish lists this step (there's lots more):

"The Open SUP uses a two-piece, double wall stainless steel
eyelet to equalize spoke nipple stress and help prevent spoke
nipple pull-through failure. Both eyelet pieces are stamped
from sheet stainless steel, the upper eyelet piece is cup shaped,
while the lower eyelet piece takes the form of a hollow rivet.
The upper piece, having an oval flange, is inserted into the
spoke hole from the interior, or tire side. Because of the
heigh between the cross-tie and spoke bed walls, the upper steel
eyelet cup is taller than occurs on many other double wall
eyelets.. The lower piece is set into the upper cup piece,
with the lower piece protruding through the spoke bed wall.
Force is applied to the top of the lower piece so a mandrel
can flare the lower piece into a smooth round blossom that
now holds both eyelet pieces firmly within the outer walls
of the cross-tie and spoke bed walls. The spoke bed wall on
the Maciv Open SUP showed no post machining distortion from
this peening process."

This sounds as if Mavic squashed the eyelets of Dave's SUP into
place on the rim harder than most manufacturers after anodizing,
but BikePro noticed no obvious damage in the way of cracks or
distortion.

If anyone has questions about rims that might be in the 1994
catalogue, I'll be glad to look them up. Unfortunately, they're
in such tiny print and hide behind so many pink background
overlays that scanning hasn't produced useful pictures.

Carl Fogel

James Thomson

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Feb 29, 2004, 2:35:52 PM2/29/04
to
"Carl Fogel" <carl...@comcast.net> wrote:

> My 1994 Pedal Pusher BikePro catalogue has a two-page
> rim table and lists Araya RM-20 rims in 24" and 26" with
> oodles of details (eighteen columns).

The BikePro catalogue is still available online. It hasn't been updated in
many years, and as a result is one of the best sources of detailed
information on older components.

http://www.bikepro.com/products/rims/rims.html
http://www.bikepro.com/guide.html

James Thomson


Carl Fogel

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Feb 29, 2004, 2:51:02 PM2/29/04
to
jobst....@stanfordalumni.org wrote in message news:<Jwf0c.4507$_3.7...@typhoon.sonic.net>...

Dear Jobst,

Elsewhere in this thread, Dave wrote:

"The braking surface is definitely concave. The braking surface *did*
show significant wear. I don't know if it was excessive. How thin does a
wall need to be in good aluminum? I don't know how thick the wall was
when the rim was new, so I can't comment on the change in thicknes. I
could measure the remaining wall thickness."

Dave also wrote:

"These sidewalls are ~1.5-1.8 mm thick at the crack."

"How do you know when to replace a rim? Concavity in the brake wall? Do
you measure the wall thickness? Based on your earlier post, I don't
think you wait until they crack."

Your answer to this question seemed about as serious as my suspicions
concerning Dave's sons:

"I have a calibrated thumb and forefinger that I pass over the rim in a
brake caliper manner feeling the hollow cheeks of the rim."

Seriously, how do you know when to replace a rim? I seem to
recall reading elsewhere on rec.bicycles.tech about worn rims
bending outward, but pictures like the ones mentioned in the post
below make me wonder how effective that is:

[start post]

From: un smowler <unsm...@yahoo.com>
To: carl...@comcast.net
Subject: Worn Out Rims
Date: Tue, 11 Nov 2003 18:53:25 -0800 (PST)

Carl: I've been reading some of the RBT threads for
lunchtime diversion recently. I was surprised that
folks with much more cycling experience than mine
had never seen worn out rims before. Attached are
photos of a completely depreciated Mavic 221 rim.
Its life was just over 2 seasons of mountain biking
in southern Maine. For me a season is 6-7 months,
2 to 3 rides/week, 2-3 hours/ride. It's about typical
rim life for me, only the failure mode is unusual.
Usually I replace rims when they've gotten a major
ding, which becomes easier and easier to do as the
rim wears. This one somehow never got that abuse.
It failed while I was trying to seat a studded tire,
at about 60 psi. As an outcome, I have gotten a bit
quicker to replace rims when they start to flare out,
and keep ear protectors handy by the floor pump!

Feel free to quote me when you post the pics. Dave D

Dear Dave,

Here are your pictures of the failed rim:

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

Thanks!

Carl Fogel

[end post]

Jobst, do you (or anyone else) have any close-up pictures
of brake-wear failures on unanodized rims that could be
put up for comparison with Dave's rim pictures? The ones
of the Mavic 221, although dramatic, aren't nearly detailed
enough to show the edges where things tore.

(I'd also like to know if unsmowler has any small children.
I can't tell for sure, but some of the damage looks like
tooth-marks.)

Carl Fogel

Benjamin Lewis

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Feb 29, 2004, 3:12:31 PM2/29/04
to
Carl Fogel wrote:

> Your answer to this question seemed about as serious as my suspicions
> concerning Dave's sons:
>
> "I have a calibrated thumb and forefinger that I pass over the rim in a
> brake caliper manner feeling the hollow cheeks of the rim."
>
> Seriously, how do you know when to replace a rim?

I think he *was* being serious. With experience, I suspect one can judge
this sort of thing to sufficient accuracy. Those of us without such
experience must presumably resort to calipers.

--
Benjamin Lewis

"Love is a snowmobile racing across the tundra and then suddenly it flips
over, pinning you underneath. At night, the ice weasels come."
--Matt Groening

jobst....@stanfordalumni.org

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Feb 29, 2004, 3:22:41 PM2/29/04
to
jim beam snipes intoxicatedly:

>>> That's quite possible. It's probably academic, though, since the
>>> rim is obviously going to be out of service anyway. Even if there
>>> were cracks that could have been found, it's unlikely that they
>>> would have been spotted prior to the failure since it's not like
>>> you're going to rip a good sew-up off of the wheel just to inspect
>>> the flanges periodically.

>> As far as I could see, this is a clincher rim and the crack should
>> be detectable on the outside when it first developed. As was
>> mentioned, it grew and failed while parked, so it must have been
>> there before it was parked. In any case, with many years of no
>> anodized rims, such failures did not occur to any of the many
>> bikies in our area. In contrast, with the advent of dark anodized
>> rims, they occurred often.

> you keep making this allegation jobst, but the only "evidence" i've
> ever seen you present that "supports" your "anodizing induced
> fatigue" theory is dye penetrant testing. all dye penetration does
> is tell you whether there is a crack detectable by that means. it
> does *NOT* analyze cause.

What are you talking about. I have never mentioned dye penetration.
What's more, you ignore that cracked rims were brought to us primarily
on the day Mavic offered the MA-40, a version of rim that not anodized
precursor (MA-2) is still performing well with no cracks and no fear
of cracking. You may not have ridden bicycles in the days before
anodized rims and the greater durability claimed for them. Those of
us who recall that day also remember how cracked rims were everywhere
after that. Reducing the anodizing thickness has ameliorated that a
little.

> you also make the [il]logical jump from the presence of a dye
> penetrant positive to the complete diagnosis of its initiation,
> propagation & eventual failure. you've never addressed the effects
> of alloy composition, environment or even spoke tension on your
> analysis - you merely assert that "it never used to happen
> before... so i therefore conclude that... ". that's not complete
> analysis and certainly no causal definition.

OK, so why do we have, as you seem to imply, poorer alloys today than
in the 1950's when none of these failures occurred even though average
roads were rougher in those days? So you are claiming that rims crack
not because they are anodized but rather that they are made of less
suitable alloys... even though the MA-2 and MA-40 were the same
extrusion to begin with.

> in the case of the above photos, which while they are too unfocused
> to show conclusive evidence of anything, /do/ arguably show some
> intergranular cracking features.

You're dodging. With experience in rims, you could readily make an
accurate assessment of this failure, knowing that such events were
unknown before anodizing. Besides, claiming that it couldn't be
caused by anodizing because it was worn off, as some have opined,
misses the point that the crack opens in tension, inside the profile,
not from the outside (brake surface) that failed last in forced
rupture.

> intergranular cracking is /not/ typical of fatigue, whether it be
> anodizing induced or not.

OH? You also don't recall the days of failed parts on older cars
where axles often broke to expose intergranular failure from which
mechanics of the day were led to say, "your axle was too old, it
crystallized" which they went on to show by the surface of the
fracture. Forced ruptures are smeared and fine in texture, fatigue
failures are rough and crystalline in aluminum used here.

> in short, this is probably a complex failure. asserting guesswork
> pertaining to only one particular potential failure element is
> amateurish. you fail to differentiate between different anodizing
> processes. what you probably are trying to say is that hard
> anodizing induced cracking, but instead you use the term "dark"
> anodizing, which is too broad a definition and includes cosmetic
> processing. normal anodizing that has been dyed is no worse than
> clear anodizing - and clear anodizing is not a problem as evidenced
> by the vast quantities of clear anodized ma2's that were sold.
> failure to differentiate between normal protective [and cosmetic]
> anodizing & hard anodizing merely serves to undermine you.

Scraping a knife over either kind of anodizing without penetrating
force, you will find a hard crust that resists scratching. You can
also inspect such surfaces under grazing incidence light and see
cracks in both hard anodizing and cosmetic anodizing. Your method of
attacking straw men does not do much convincing for those who are
aware of these techniques of argumentation. I haven't seen you point
out why these rims crack other than saying that it isn't anodizing.

When are you going to find the shift key on your KBD? Your modernist
lower case writing is tedious to read.

Jobst Brandt
jobst....@stanfordalumni.org

jobst....@stanfordalumni.org

unread,
Feb 29, 2004, 3:35:05 PM2/29/04
to
Mike Shaw writes:

>> As far as I could see, this is a clincher rim and the crack should
>> be detectable on the outside when it first developed. As was
>> mentioned, it grew and failed while parked, so it must have been
>> there before it was parked. In any case, with many years of no
>> anodized rims, such failures did not occur to any of the many
>> bikies in our area. In contrast, with the advent of dark anodized
>> rims, they occurred often.

> Hey Jobst,

> How many of those rims that never failed were actually clinchers?
> Yah, I know you love MA2s, but the rest?

I haven't thrown many rims away other than the ones I inspected at the
local bicycle shops, Wheelsmith, Palo Alto Bicycles, Bicycle Outfitter
and some others. Therefore I have a stack of about 40 rims, among
them some tubulars that I can inspect and not find sidewall cracking.
At best there are some that had short in-line cracks at the eyelets
that ceased to grow because the steel socket inside took up the load
and served until the rim was retired either for worn brake faces or
dents. Along with anodizing, un-socketed rims are and additional
hazard.

> What were the percentage of people riding tubulars vs. clinchers?

What does it matter other than more red herrings. This gets tiresome.
How about explaining in plain English what causes these failures in
contrast to rims that were not anodized instead of attacking any and
all analyses of what we see.

> Ya think that maybe, just maybe, that some sidewall failures may
> have something to do with about a cm of unsupported metal being
> stressed by holding together a clincher inflated to 110psi+?

No! I do that all the time.

> Next question: what weight were those clincher rims that never
> failed? 400g, 500g?

Exactly the same as the anodized version that failed. I guess you
haven't been reading any of this over the last 10 years.

> Just curious... since I haven't been studying stuff like this for
> as long as you have.

You might Google into the reams of discourse prompted by anodizing
enthusiasts like you.


Jobst Brandt
jobst....@stanfordalumni.org

jobst....@stanfordalumni.org

unread,
Feb 29, 2004, 4:46:37 PM2/29/04
to
Carl Fogel writes:

> Jobst, do you (or anyone else) have any close-up pictures of
> brake-wear failures on unanodized rims that could be put up for
> comparison with Dave's rim pictures? The ones of the Mavic 221,
> although dramatic, aren't nearly detailed enough to show the edges
> where things tore.

I don't have any among all the worn and dented rims in my collection,
none of which are anodized. The claim that rims bend outwards when
they wear thin, in my experience, is an incorrect assessment. These
rims have been worn hollow and to casual observance appear to be
flared out. My worn out rims looked that way too but were in fact
unchanged when measured internally.

Jobst Brandt
jobst....@stanfordalumni.org

jobst....@stanfordalumni.org

unread,
Feb 29, 2004, 4:50:51 PM2/29/04
to
Benjamin Lewis writes:

>> Your answer to this question seemed about as serious as my
>> suspicions concerning Dave's sons:

>> "I have a calibrated thumb and forefinger that I pass over the rim
>> in a brake caliper manner feeling the hollow cheeks of the rim."

>> Seriously, how do you know when to replace a rim?

> I think he *was* being serious. With experience, I suspect one can
> judge this sort of thing to sufficient accuracy. Those of us
> without such experience must presumably resort to calipers.

Since the bead crown of the rim does not wear with reasonably adjusted
brakes, measuring with calipers and knowing that the original wall
thickness was 1.5mm, the resulting wall can be assessed within reason.
As I said, this can also be done by wiping thumb and forefinger across
the brake track.

Jobst Brandt
jobst....@stanfordalumni.org

jim beam

unread,
Feb 29, 2004, 7:42:20 PM2/29/04
to
jobst....@stanfordalumni.org wrote:
<snip>

> What are you talking about. I have never mentioned dye penetration.
> What's more, you ignore that cracked rims were brought to us primarily
> on the day Mavic offered the MA-40, a version of rim that not anodized
> precursor (MA-2) is still performing well with no cracks and no fear
> of cracking. You may not have ridden bicycles in the days before
> anodized rims and the greater durability claimed for them. Those of
> us who recall that day also remember how cracked rims were everywhere
> after that. Reducing the anodizing thickness has ameliorated that a
> little.

"I have never mentioned dye penetration." well, it's certainly what you
were referring to here:

http://groups.google.com/groups?selm=9%25x_a.11466%24dk4.433979%40typhoon.sonic.net&oe=UTF-8&output=gplain

either you have done dye penetrant testing for cracks in rims or you
haven't. which is it?

in addition, you assert that the ma2 is not anodized. it most
definitely was available in clear anodized. i have one. in fact, i've
even taken the trouble to specifically look for ma2's since we first
started this little love-fest, and guess what? only 1 of the 30-odd
silver ma2's i have inspected has been unanodized, [and that had
corrosion issues]. so, while you may be the guy that managed to
stockpile the last of the small number of unanodized ma2's that were
ever imported, the poor unsuspecting masses have had to put up with
clear anodized ma2's, so kindly adjust your rhetoric. and if you still
don't believe me, take a look at the old mavic catalog for confirmation
of the silver anodized ma2's existence.

<snip>


> OK, so why do we have, as you seem to imply, poorer alloys today than
> in the 1950's when none of these failures occurred even though average
> roads were rougher in those days? So you are claiming that rims crack
> not because they are anodized but rather that they are made of less
> suitable alloys... even though the MA-2 and MA-40 were the same
> extrusion to begin with.

your implication, not mine. modern alloys have much better yield &
u.t.s. with better weldability. "suitability" depends on the overall
objective. if you want a rim that is strong enough to deal with
ultra-dished wheels and lower spoke counts, than yes, modern alloys are
better. as a component whose predominant failure mode [outside of sunny
california] is braking surface wear, i see no problem with having a rim
have a higher chance of cracking at higher mileage if physical wear
predominates and the other primary design criteria are better met.

<snip>


> You're dodging. With experience in rims, you could readily make an
> accurate assessment of this failure, knowing that such events were
> unknown before anodizing. Besides, claiming that it couldn't be
> caused by anodizing because it was worn off, as some have opined,
> misses the point that the crack opens in tension, inside the profile,
> not from the outside (brake surface) that failed last in forced
> rupture.

dodging what? those pics are inconclusive. unless you are telling us
that you've had an identical failure and that it's been properly
analyzed by an appropriate specialist, then you can't feed us what then
amounts to conjecture and guesswork. your assertion that "such events
were unknown before anodizing" makes absolutely no account of changes in
alloy, heat treatment, eyelet design, etc. etc. it's just a wildly
emotive statement.

snip>


> OH? You also don't recall the days of failed parts on older cars
> where axles often broke to expose intergranular failure from which
> mechanics of the day were led to say, "your axle was too old, it
> crystallized" which they went on to show by the surface of the
> fracture. Forced ruptures are smeared and fine in texture, fatigue
> failures are rough and crystalline in aluminum used here.

since when did a hot [or cold] forged carbon steel axle have the same
microstructure as an extruded alloy rim? what effect does carbon
diffusion have on this extruded alloy rim? how about sulfides? this is
a complete red herring.

<snip>


> Scraping a knife over either kind of anodizing without penetrating
> force, you will find a hard crust that resists scratching. You can
> also inspect such surfaces under grazing incidence light and see
> cracks in both hard anodizing and cosmetic anodizing. Your method of
> attacking straw men does not do much convincing for those who are
> aware of these techniques of argumentation. I haven't seen you point
> out why these rims crack other than saying that it isn't anodizing.

what you are saying jobst, yet again, is that there is only one element
in this failure equation, anodizing, and i am telling you, yet again,
that it's not as simple as that. there are many elements, which do
include anodizing, but also include alloy composition, heat treatment,
hot & cold work history, mechanical design and chemical environment. to
make a blanket statement essentially saying "it's anodizing - end of
story" is as accurate as your mechanic saying "your axle was too old, it
crystallized".

dvt

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Feb 29, 2004, 8:23:35 PM2/29/04
to
jobst....@stanfordalumni.org wrote:
> He [Dave] also made the claim in contrast to other postings that these rims

> do not fail in a dange4ous manner.

I don't think I said that, or anything that resembles that. I *did* say
that the rim was probably worn enough to be retired, and I probably
should have retired it earlier.

> To
> visualize the danger one must either ride in traffic or descend
> mountain roads that border precipices.

Just did both of those today. Routine. As a matter of fact, remember the
snowbank episode I mentioned earlier? Good thing for the snowbank. It
kept me from falling off one of those precipices.

Dave
dvt at psu dot edu

Carl Fogel

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Feb 29, 2004, 8:55:31 PM2/29/04