RE: [CR]Broken Retro Crank Example

(Example: Framebuilders:Dario Pegoretti)

Date: Thu, 12 Apr 2001 05:23:14 -0600
To: "Stockwell, Brad" <BRAD.STOCKWELL@mpp.cpii.com>, "'M4Campy'" <M4Campy@aol.com>
From: "Bicycle Classics inc" <bikevint@tiac.net>
Subject: RE: [CR]Broken Retro Crank Example
Cc: "Stockwell, Brad" <BRAD.STOCKWELL@mpp.cpii.com>, Classicrendezvous@bikelist.org


My guess is that Campy cranks are much less likely to break if under 10K of use, but that is only a hunch. Conversely, an east coast trackie called "Moose" once told me that he broke 17 Campy cranks and many were brand new. It really comes down to a game of both statistics and how the crank is used. Certain ways of stressing the crank may make it more likely to fail, but there is also a tremendous stochasic element to when and if the crank fails. Similarly, people can have horrible illnesses when young, but statistically it is much more likely when we're older. At the same time, some families have genetic predispositions to terrible childhood illnesses which for them changes the odds.

Unfortunately, many folks behave as though a component failure on any given pedal stroke is a statistically independent event from the pedal strokes that came previously. Hence the notion "my Viscount fork won't break because I pedaled it lots of times and it never broke before". That is just plain nuts! Unfortunatly, the same folks may then go purchase lottery tickets at a store that is known for being "lucky" - which is equally as nuts, as success from buying lottery tickets, if the numbers are randomly distrubuted, is an independent event.

Mike "about time I used something from that stats course" Kone

At 03:54 PM 4/12/01 -0700, Stockwell, Brad wrote:
>Mike Wilkinson wrote:
> Ok, now I'm getting nervous. Since I never saw but always
>heard
> of Campy crank failure what should I look out for. Stress
>crack
> along the pedal and stamp areas? Will there be any squeaks
>or a
> sign that impending doom and road-rash await?
>
> Of course, at around 130lbs should I worry???
>
>
>
> 1) I don't know how many miles my crank had on it, but
>probably lots. It was a pre-77 crank purchased from the 'used' pile at a
>local shop. I put 1200 miles on it over about 4 months, then it broke. It
>had strap rub marks and scrapes in various spots.
>2) For comparison, I'm just over 6ft and weigh 165lb.
>3) Last year someone on the list suggested that NR cranks might be low
>risk for the first 10,000 miles, if I recall correctly.
>4) I was extremely lucky: it broke when I was cruising through my
>neighborhood, standing up to start from a stop sign. It could have been
>much worse: the prior weekend I had sprinted out-of-the-saddle down a 5%
>grade trying to keep up with my triathlete neighbor who was going almost 40
>mph!
>
> Brad 'Glad it was only Road Rash' Stockwell
> Palo Alto