ISIS or OL crank with Campy?

THanks,
Jim A

My new Six13 comes stock with a FSA Octalink carbon crank and Campy
Centaur. I would think the only consideration should be getting the
correct BB for the correct chainline.

You should be aware that Shimano dropped the Octalink crank for cause,
although the old conspiracy theory lives that this was done to force
people to re-equip their bicycles to keep current. The Octalink
spindle attachment, not being a press fit, does not transmit reverse
torque without a some rotary movement, movement that unscrews the
retaining bolt. This occurs relatively quickly for riders who when
standing on both pedals, consistently have the right foot forward
(goofy footed). Since most riders do this occasionally anyway, it is
only a matter of time before spline failures occur and more often than
with square tapers. Hence the new FC-7800 BB.

http://tinyurl.com/o2du

ISIS has had its problems as well but they are not as apparent. I
doubt that anyone has done solid modeling of this interface to asses
where the highest stresses occur. In contrast square tapers have two
modes of failure, both resulting from a small dimensioned square (the
size of the last joint of an average little finger) and a high press
fit that together with torque and bending cause crank splitting and
spindle failures within the left end press fit.

All I can say is that we aren't there yet but Shimano is at least
working on it. I hope they computer modeled stress distribution. At
least it looks as though there was some serious thought there.

Jobst Brandt
jobst....@stanfordalumni.org

Is ISIS/Octalink an interference fit? Isn't this enough to prevent
unscrewing, or is there not enough reactive normal force on the bolt to keep
it on?

--
Phil, Squid-in-Training

The design of ERGO makes it possible to use any crank with Campagnolo BUT I
would stay away from Octalink, as shimano is abandonng this 'standard' and in
the near future(say about 3 years) you will not find these. ISIS, plentiful,
not limited by one manufacturer's license, etc.

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

In the absence of a press fit and with a straight spline, backlash
clearance exists in this interface. Elastically, even with no
clearance, one face compresses while the other lifts off. Although in
theory this makes the torsional rigidity of the spline 1/2 as great as
with a press fit, together with actual clearance, it is enough to
cause the retaining bolt to back out. The bolt "normal force" does
nothing to resist backlash movement, it being normal to the plane of
action. Actual and elastic backlash will not tighten the bolt but it
can and has loosened it.

I have mentioned this in the past and believe that Shimano also
discovered this failing which caused them to discontinue this as
their mainstay. FC-7800 is there for real reasons.

Jobst Brandt
jobst....@stanfordalumni.org

On Peter's advice, I went with ISIS.

does that link support your argument? how do /you/ support that
argument? and how does the 7800 design specifically address lash other
than it being possible to tighten the clamp circumferentially - it still
has parallel axial splines. theoretically, the interference of a taper
addresses that problem better - like the shaft of an octalink spindle.
/my/ octalink cranks have been absolutely "fit & forget". maybe correct
torque simply needs to be observed.

While I wouldn't at all debate the analysis you include here I would
question the statistical relevancy, especially as it applies to square
taper BBs. I am the first to admit the frustration at the amount of
flex they allow but frankly spindle or crank/spindle failure is the
least of my concerns relative to other points of failure in bicycles,
though I am always aware they could fail.

I am not baiting here.. this is a serious inquiry- is any of this
relevant given all of the other machanical failure modes, not only with
other bicycle parts but relative to other machanical things we regularly
use without consideration to their potentially injurious failure modes?

Personally, I think the Cannondale has the most robust interface but it
is proprietary. However, I think ISIS is a fine interface and wish it
was making more headway, especially in road products. But I have never
done serious analysis on it either.

Thanks in advance,

Terry

> While I wouldn't at all debate the analysis you include here I would

As one user and possibly observant of others who use the equipment,
you are not necessarily privy to the general failure rate of a
component. Being a bit heavier and riding over a larger range of
surfaces than many riders, I have experienced many failures of
spindles and cranks, cranks that have failed at either end. The
failure rate was until recently about one or more every 10,000 miles.
That adds up to more than 30 crank failures, the earlier ones leading
to falls until I began a rigorous inspection regimen. These were both
Campagnolo Record and Shimano DuraAce.

> Is any of this relevant given all of the other mechanical failure

> mechanical things we regularly use without consideration to their
> potentially injurious failure modes?

The argument that "it hasn't happened to me" should be presented with
caution. I know others who believed that, feeling I had a little
black cloud over my bicycle, until they fell in traffic. If the left
crank fails when standing (as is common starting at intersections) the
rider falls to the left and hopes not to be next to a readymix truck
or city bus.

I think that the Octalink and Cannondale attachments would be greatly
improved if they had a retaining bolt with the ratcheting face that
cassette hubs have on the sprocket retaining crew. Particularly the
Octalink, because it does not rely on being tight to transmit its
loads. I can't say the same for Cannondale or ISIS.

I have given it serious thought and at least solved crank failure at
the pedal eye as I have explained. Now I don't have to minutely
inspect the cranks once a week for cracks. I have no way of checking
for spindle fatigue because that failure occurs inside the press fit
of the square taper. I hope intermittent replacement of the spindle
will keep me safe there although it is only the left end that fails
there, the worser of the two ends.

Jobst Brandt
jobst....@stanfordalumni.org

> ... This occurs relatively quickly for riders who when

> (goofy footed)....

Why is having the right foot forward "goofy footed"?

--
Tom Sherman

When engaged in activities such as skateboarding, snowboarding,
surfing, or standing on both pedals, most people preferentially lead
with the left foot. The accepted term for those who lead with the
right is "goofy footed."