mavic d521 rim cracks?

I run the d-521 on my trail bike as a rear, has about 1600 miles of nasty rocky singletrack with no
problems. They are on Hadley hubs with 2.0 SG SS spokes. The coating does wear off the rims I'm
using Avid Vee's for brakes with XTR extreme pads. I hear the rim is not best for disc breaks due to
the eyelets issue. More torque through single eyelets not ideal due to disc forces on the wheel.
Otherwise very strong thick rim, its heavy but its a downhill rim. If you want a great rim for disc
brakes get the Atomic "Trail Pimps"

Tauras kcbx.netsurfreportOpen ↗

"gerrit van wijk" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

My bikeshop tells me Mavic d521 very strong long lasting rims, perfect for loaded touring and
mountanibiking. But I found a review stating the ceramic chips of very easy and cracks

form

Quoted message said:

around the (single) eyelets. Does anybody have simular problems?

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Minor cracks radiating around the eyelet are usually just the anodizing and are present when new.
They can be disregarded.

Mavic used to have some extrusion problems which caused circumferential cracks around the rim, often
starting at spoke holes, but I think Mavic pretty much have that under control these days.

Regarding the ceramic braking surface, sure, it can chip, but ceramic II is better than their
original, and unless you lose a /lot/ of the coating, it makes no practical difference to use.

Jim

gerrit van wijk said:

My bikeshop tells me Mavic d521 very strong long lasting rims, perfect for loaded touring and
mountanibiking. But I found a review stating the ceramic chips of very easy and cracks form around
the (single) eyelets. Does anybody have simular problems?

I can kind of agree with these statements. I had 517's that showed stress marks (very fine cracks)
at the eyelets. I freaked out. I ordered new 519's to get a stronger rim and kept riding until they
failed. They didn't fail. I replaced the rear when the freehub died on a night ride since I had
another rim ready to go. I am still running the front. I am now 3 years into these things. I could
put a new freehub on the 517 and ride it more. I just haven't.

I also took them to the shop and the wrench said don't worry. He said the only problem is when they
crack from one eyelet to the next. I am talking about a 517 (light rim) and 519 (stronger free ride
rim) but that 521 is huge compared to these. I wouldn't worry too much. Take it to the LBS and see
what they say.

GP

--
members.cox.netgporter1970Open ↗ "jim beam" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Minor cracks radiating around the eyelet are usually just the anodizing and are present when new.
They can be disregarded.

Mavic used to have some extrusion problems which caused circumferential cracks around the rim,
often starting at spoke holes, but I think Mavic pretty much have that under control these days.

Regarding the ceramic braking surface, sure, it can chip, but ceramic II is better than their
original, and unless you lose a /lot/ of the coating, it makes no practical difference to use.

Jim

gerrit van wijk said:

My bikeshop tells me Mavic d521 very strong long lasting rims, perfect

for

Quoted message said:

Quoted message said:

loaded touring and mountanibiking. But I found a review stating the ceramic chips of very easy
and cracks

form

Quoted message said:

Quoted message said:

around the (single) eyelets. Does anybody have simular problems?

George L. Porter said:

I can kind of agree with these statements. I had 517's that showed stress marks (very fine cracks)
at the eyelets. I freaked out. I ordered new 519's to get a stronger rim and kept riding until
they failed. They didn't fail. I replaced the rear when the freehub died on a night ride since I
had another rim ready to go. I am still running the front. I am now 3 years into these things. I
could put a new freehub on the 517 and ride it more. I just haven't.

This is all old hat and has been aired here often. Anodizing causes rim fractures that initiate from
fine surface cracks occurring in the hard and brittle anodized surface. Even before any spokes are
tightened, these cracks are already there, caused by insertion and crimping of eyelets. If the wheel
is heavily stressed in use, these cracks grow to the extent that whole sections of rim break out.
When the anodizing fad began and rims were more heavily anodized, some rims split circumferentially
in the middle of the braking track, leaving two interlocked hoops, the tie still mounted on the
outer part.

If bicyclists would not have such a desire for aluminum rims that don't look like aluminum, aka dark
non shiny colors, then we wouldn't have this expensive source of rim failure.

Jobst Brandt [email hidden] Palo Alto CA

jim beam said:

Mavic used to have some extrusion problems which caused circumferential cracks around the rim,
often starting at spoke holes, but I think Mavic pretty much have that under control these days.

I lost a 36h D521 that way in 2001, bike was built 2000.

--
MfG/Best regards helmut springer

With the greatest of respect, the hooping cracks are extrusion problems. This is evident from
metallographical examination.

Yes, you are correct that cracking anodizing /can/ initiate fatigue, but it's not commonly what we
see in practice - for rims at any rate. Anodizing raises compressive surface stresses, and this
helps mitigate crack initiation. /All/ aluminum is anodized to some degree, just by exposure to air.
The color which the anodizing has been stained is not relevant.

Jim

Quoted message said:

George L. Porter said:

I can kind of agree with these statements. I had 517's that showed stress marks (very fine cracks)
at the eyelets. I freaked out. I ordered new 519's to get a stronger rim and kept riding until
they failed. They didn't fail. I replaced the rear when the freehub died on a night ride since I
had another rim ready to go. I am still running the front. I am now 3 years into these things. I
could put a new freehub on the 517 and ride it more. I just haven't.

This is all old hat and has been aired here often. Anodizing causes rim fractures that initiate
from fine surface cracks occurring in the hard and brittle anodized surface. Even before any
spokes are tightened, these cracks are already there, caused by insertion and crimping of eyelets.
If the wheel is heavily stressed in use, these cracks grow to the extent that whole sections of
rim break out. When the anodizing fad began and rims were more heavily anodized, some rims split
circumferentially in the middle of the braking track, leaving two interlocked hoops, the tie still
mounted on the outer part.

If bicyclists would not have such a desire for aluminum rims that don't look like aluminum, aka
dark non shiny colors, then we wouldn't have this expensive source of rim failure.

Jobst Brandt [email hidden] Palo Alto CA

Jim Beam said:

Quoted message said:

Quoted message said:

I can kind of agree with these statements. I had 517's that showed stress marks (very fine
cracks) at the eyelets. I freaked out. I ordered new 519's to get a stronger rim and kept riding
until they failed. They didn't fail. I replaced the rear when the freehub died on a night ride
since I had another rim ready to go. I am still running the front. I am now 3 years into these
things. I could put a new freehub on the 517 and ride it more. I just haven't.

Quoted message said:

Quoted message said:

This is all old hat and has been aired here often. Anodizing causes rim fractures that initiate
from fine surface cracks occurring in the hard and brittle anodized surface. Even before any
spokes are tightened, these cracks are already there, caused by insertion and crimping of
eyelets. If the wheel is heavily stressed in use, these cracks grow to the extent that whole
sections of rim break out. When the anodizing fad began and rims were more heavily anodized, some
rims split circumferentially in the middle of the braking track, leaving two interlocked hoops,
the tie still mounted on the outer part.

Quoted message said:

Quoted message said:

If bicyclists would not have such a desire for aluminum rims that don't look like aluminum, aka
dark non shiny colors, then we wouldn't have this expensive source of rim failure.

Quoted message said:

With the greatest of respect, the hooping cracks are extrusion problems. This is evident from
metallographical examination.

Flattery will get you nowhere! metallographical? Wow!

By whom? The anodizing was the only difference, the extrusions at that time being available in shiny
aluminum and black hard anodized. I took samples of each and have the dyed and polished cross
section photos done by a metallurgical laboratory at Alcan that show cracks propagating from the
anodizing into the base metal in the anodized version and no cracks at all in the plain version of
the same rim, the MA-2 and MA-40, the latter having cracked circumferentially. Both rims had
substantial use. The plain one was bent in a crash.

Quoted message said:

Yes, you are correct that cracking anodizing /can/ initiate fatigue, but it's not commonly what we
see in practice - for rims at any rate. Anodizing raises compressive surface stresses, and this
helps mitigate crack initiation. /All/ aluminum is anodized to some degree, just by exposure to
air. The color which the anodizing has been stained is not relevant.

The way you say that one might guess that you work for Mavic. The natural oxide on a polished rim is
possibly 0.01mm thick at best and has so little strength that it cannot but craze on the microscopic
level under stress. That is, the skin is so weak that it cannot effect the base metal. Besides, the
structure of that surface is not the same as anodizing.

Jobst Brandt [email hidden] Palo Alto CA

Quoted message said:

I took samples of each and have the dyed and polished cross section photos done by a metallurgical
laboratory at Alcan that show cracks propagating from the anodizing into the base metal in the
anodized version and no cracks at all in the plain version of the same rim, the MA-2 and MA-40,
the latter having cracked circumferentially. Both rims had substantial use. The plain one was bent
in a crash.

Good! Science! Can you post the pics?

Question: By "section", do you mean that you examined a longitudinal section also? The etched
samples I've seen show defect lines clearly running along the extrusion axis. The cracks merely
followed the line of these defects. The fact that anodizing cracks radiate around an eyelet, and
some [naturally] follow the extrusion axis, may arguably exacerbate the problem, but are not the
primary cause from what I can see. The rough, somewhat granular nature of the fracture surface
should be sufficient proof of inter-granular crack propagation, [extrusion] rather than
trans-granular [fatigue].

tandem-fahren.deimm022a.jpgOpen ↗
tandem-fahren.deimm032a.jpgOpen ↗ These two failures can by no means be
attributed to cracked anodizing radiating from spoke eyelets for example. Note also how the second
picture shows one fracture changing plane no less than 5 times, each following an extrusion band.
And not being arrested when encountering an [unstressed] spoke hole! Definitely not fatigue
fracture behavior.

Quoted message said:

The way you say that one might guess that you work for Mavic.

No.

On the subject of fatigue, there's a book well worth reading: Deiter - Mechanical Metallurgy. ISBN
0-07-016893-8. Chapter 12-9 has an interesting and relevant section on fatigue nucleation. It
specifically discusses nucleation at surface defects, including small features like slip bands. This
fatigue initiation mechanism is particularly interesting for the debate on spoke failure.

Jim