Mitigating crank failure

Quoted message said:

dvt said:

Quoted message said:

Phil, Squid-in-Training wrote:

>Crack propagation on cranks breaking at midsection is invariably started
>with shoe rub.

Quoted message said:

Is it?

http://pardo.net/pardo/bike/pic/fail/crank-fail-002.jpg

pedal eye failure (not at midsection)

Quoted message said:

http://www.atmosp.physics.utoronto.ca/people/amit/crank.htm

midsection, in region of shoe rub

Quoted message said:

http://pardo.net/bike/pic/fail-001/CrankmodXthree.jpg

pedal eye failure (not at midsection)

Quoted message said:

http://www.yellowjersey.org/jayscranks.html

midsection, in region of shoe rub

Quoted message said:

http://www.yellowjersey.org/photosfromthepast/yesdeydo.jpg

pedal eye failure (not at midsection)

Quoted message said:

http://pardo.net/pardo/bike/pic/fail/FAIL-001.html

pedal eye failure (not at midsection)

None of these photos contradict Phil's assertion. And of course they
don't confirm his assertion, since only one contradictory example needs
to be shown.

--
Dave
dvt at psu dot edu

Phil Squid used the term "invariably". The online dictionary says
invariably means "Not changing or subject to change; constant". From
the pictures above you can easily deduce that shoe rubbing is not a
constant/invariable beginning of crankset cracking.

but it does seem to be a high correlation with show rubbing for
mid-section failure.

Quoted message said:

I think a reading
of the FAQ and Brandt's postings about crankset cracking would provide
a better cause and understanding than shoe rubbing.

brandt doesn't know much about the initiation &/or propagation of fatigue.

Quoted message said:

These pictures are
the ones found posted on this forum. I am sure there are other
pictures on the web showing all manner of crankset failure.

you'd think, but there aren't many. if you can find a modern dura-ace
or campy record/chorus crankset that's fatigued at the pedal eye, that
would be particularly interesting.

Phil said:

With another customer's broken crank coming in this week for replacement,
I've been thinking... is there a better solution to all these broken cranks?

Crack propagation on cranks breaking at midsection is invariably started
with shoe rub. Since nobody would pay for cranks with a "shoe rub shim" on
it, why not sell shoes that have felt/terrycloth/foam bits that cover the
inside of the ankle? This would be unobtrusive, could be dyed the color of
the shoe, and cut down on deeper cuts in the metal that would start cracks.

These shoes could be sold to the radonneur/brevet/messenger/commuter/old
fart group of riders that would appreciate such a feature.

Thoughts?

the crank manufacturer is important. some designs are much more prone
to fatigue initiation on minor damage than others, notably the "I"
cross-section profiles. the smoother "oval" profiled ones like modern
campy & dura-ace are much less susceptible.

shoes with grit-retainers are not a good idea - increased abrasion.

if a customer cannot be persuaded to adopt a more crank-friendly cleat
position, then application of a scuff-resistant coating may be a good
idea. old inner tube sleeved over the crank arm might work.

personally, i can't imagine how anyone can ride with their shoes
scuffing like that - it would drive me nuts.

jim beam wrote:

(In reply to someone who posted):

Quoted message said:

Quoted message said:

These pictures are
the ones found posted on this forum. I am sure there are other
pictures on the web showing all manner of crankset failure.

(JB's reply):

Quoted message said:

you'd think, but there aren't many.

Here's my favorite:
http://technology.open.ac.uk/materials/mem/mem_ccf4.htm
--D-y

Quoted message said:

jim beam wrote:

(In reply to someone who posted):

Quoted message said:

Quoted message said:

These pictures are
the ones found posted on this forum. I am sure there are other
pictures on the web showing all manner of crankset failure.

(JB's reply):

Quoted message said:

you'd think, but there aren't many.

Here's my favorite:
http://technology.open.ac.uk/materials/mem/mem_ccf4.htm
--D-y

i think that's my "favorite" too. last few bike swaps i've been to,
every single used campy crank that vintage had cracking evident in that
exact same spot. it's a result of the spider/crank arm machining profile.

Ron Ruff said:

Phil said:

With another customer's broken crank coming in this week for
replacement, I've been thinking... is there a better solution to all
these broken cranks?

Seems like avoiding contact altogether would be preferable, by moving
the feet farther out... longer spindles or an extension of some kind.

But the q-factor!

Quoted message said:

Some cranks are better than others, too. What sort of cranks are you
seeing this on?

It was a highly polished FSA alu with 2k miles on the clock. It had a huge
curve coming out of the crank spider, a prime place for shoe rub.
--
Phil, Squid-in-Training

Phil said:

Ron Ruff said:

Seems like avoiding contact altogether would be preferable, by moving
the feet farther out... longer spindles or an extension of some kind.

But the q-factor!

Quoted message said:

Some cranks are better than others, too. What sort of cranks are you
seeing this on?

It was a highly polished FSA alu with 2k miles on the clock. It had a huge
curve coming out of the crank spider, a prime place for shoe rub.

So, I guess it was either an Energy (hollow rectangular) or a Gossamer
(solid with diamond profile). I'd guess that the Energy is more prone
to this.

I seems to me that crank arms should make a straight line from the BB
spindle to the pedal spindle... or even curve the opposite way that
they tend to (maybe an S curve?). The limiting Q-factor should be
hitting the chainstay with the heal or ankle, and not the crank arm. I
like low Q, myself...

Squid-in-Training said:

With another customer's broken crank coming in this week for replacement,
I've been thinking... is there a better solution to all these broken cranks?

Crack propagation on cranks breaking at midsection is invariably started
with shoe rub. Since nobody would pay for cranks with a "shoe rub shim" on
it, why not sell shoes that have felt/terrycloth/foam bits that cover the
inside of the ankle? This would be unobtrusive, could be dyed the color of
the shoe, and cut down on deeper cuts in the metal that would start cracks.

3M made an antiabrasion tape for the leading edge of helicopter blades
to keep the surface from being pitted by flying sand. They make a
number of other protective tapes that would likely be useful for
protecting against shoe scuffs. The problem I see is this: Out of
the large number of cranks that you sell, what percentage actually
fails, and what's the likelihood that you'd get people to accept the
tape's presence in the first place, that they'd leave it in place,
and/or that they would replace it if it got torn up? If the customer
is concerned about the issue, sure, it's an easy sell...but if they
aren't, it's going to look like snake oil...and aren't most of the
broken cranks on bikes whose owners have never had that happen before?
How easy would it have been to sell them on the idea of something to
prevent a problem that they've never had, even one which endangers the
family jewels? (That latter consideration goes for your shoe ideas as
well, obviously...)

Quoted message said:

These shoes could be sold to the radonneur/brevet/messenger/commuter/old
fart group of riders that would appreciate such a feature.

Thoughts?

--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.