Re: [CR] Campagnolo NR Crank Failure

(Example: Framebuilders:Alex Singer)

From: <hersefan@comcast.net>
To: "lennys_email@juno.com" <lennys_email@juno.com>, classicrendezvous@bikelist.org
Subject: Re: [CR] Campagnolo NR Crank Failure
Date: Wed, 14 Dec 2005 20:35:31 +0000


A key thing that must be remembered also is the smoothness of the rider. Fatigue failure as I understand it from my engineer friends is related to peak moment stresses on the cranks. A rider who is extremely smooth and puts half the peak moment on the crank will enjoy 4 times the fatique life if my understanding is correct. So riding style is very important.

Also, failures are most likely at the left arm near the pedal. Relatively few cranks fail at the spinder as I understand it.

I once met a person who clamied to have broken about 15 campy arms if I recall - his nickname was Moose, and he often broke fresh cranks on the track. He switched to another brand.

The notion that "the crank hasn't failed yet so I'm not worried" is crazy. Your sense of security will be greatest if you base it on such logic the moment before your crank fails.

It is important to examine your cranks, but I don't think it is possible to identify a failure that is about to occur near a pedal. Perhaps I'm wrong - but I wouldn't depend on inspection to give you peace of mind.

If all you do is sit and spin, then a crank failure isn't likely to be a big deal. But if you are standing and sprinting, given the ages of most of us on the list, a failure could be a health dissaster. That is why I don't ride hard on cranks that I believe have high miles. When I ride Campy NR/SR cranks hard, I always try to be sure I'm on a fairly low mile pair and hope that Moose wasn't riding on them before me!

Mike Kone in Boulder CO


-------------- Original message --------------
From: "lennys_email@juno.com"

> Greetings All.

\r?\n> I have previously looked into the matter of NR crankset stress cracks so

\r?\n> mewhat extensively when I got my first set a few years ago, and learned

\r?\n> the following:

\r?\n> Does the NR crankset ever fail ?

\r?\n> Yes. Especially with strong riders using the same cranks over many seaso

\r?\n> ns. I have seen good pictures of such failures, as well as among other b

\r?\n> rands, on the web, but can’t remember the site. A google search for "c

\r?\n> rank failure" or the like should do it.

\r?\n> A older mechanic/racer told me that he had snapped two of them during sp

\r?\n> rints years ago before deciding to permanently switch to another brand.

\r?\n> At a very fit 175 lbs, he certainly looked capable of putting trememendo

\r?\n> us force on the cranks. He told me that non-racers weighing less than hi

\r?\n> m need not worry, unless the crank is damaged during a crash thus weaken

\r?\n> ing its ability to absorb further stress.

\r?\n> Conversely, Richard Sachs told me that he had never seen one break.

\r?\n> Conversely, Jobst Brant told me he had seen many break, not only at the

\r?\n> spider but also at the pedal eye.

\r?\n> Conversely, Alan, the previous owner of bike classics, told me that he h

\r?\n> ad seen only a couple break in 20 or so years. He said it was a premium

\r?\n> part built in great number to great success and that I should enjoy the

\r?\n> cranks but inspect for cracks annually at least and discard at first sig

\r?\n> n, as, unlike steel, aluminum when it fails does so catastrophically. I

\r?\n> took his advice and am crack-free so far.

\r?\n> Does filing before cracks are seen help ?

\r?\n> The jury is out on this one. The argument in favor being that the thin s

\r?\n> pider/crank interface allows easier crack propogation than the thicker i

\r?\n> nterface that results from filing. Like trying to tear a phone book with

\r?\n> out starting at an angle.