Re: [CR]Cottered Crank Safety


Date: Mon, 09 Jul 2001 23:28:35 -0700
To: tomwitkop@juno.com, lenoremeyer@hotmail.com
From: Joseph Bender-Zanoni <jfbender@umich.edu>
Subject: Re: [CR]Cottered Crank Safety
Cc: Classicrendezvous@bikelist.org
In-Reply-To: <20010709.222152.-940135.5.tomWitkop@juno.com>


The real issue here is steel. Steel is an inherently safer design material than aluminium for a component that is cyclically loaded and subject to fatigue. If designed within the fatigue limit it will not fail. Every aluminium component subject to cyclic loading is doomed to eventual failure, the question is when.

Anyone hear of high quality steel cranks breaking? I just started riding a set this week this week with wispy thin triangular arms. I swear I can feel the flex when I heave on them. That set is 50 years old. I have BSA cranks that are 70 years old or so but they are quite beefy in comparison.

My 1959 or so Frejus track bike had a Campagnolo Record cotterless crank with a one inch pitch chainwheel.

I have a set of the TA sort of cottered cranks (up and running now, thanks to Sheldon)and I suppose they distribute the stresses a bit better than an ordinary cottered design by driving a bit on the squared off axle flank as well as the "cotter". I remember SR making cottered alloy cranks for department store bikes that were rubbish.

Joe

At 10:21 PM 7/9/01 -0400, tomwitkop@juno.com wrote:
>I believe that before the 1970s, track racers used only cottered cranks
>because they were considered stronger and less likely to fracture then
>Cotter less cranks. I imagine this is because cottered cranks are built
>of steel which is probably stronger and certainly more forgiving than
>aluminum. I am not aware of any aluminum Cotter less cranks (I do not
>believe that the TA semi cottered cranks really counts as a cottered
>crank). Consequently, I believe that cottered cranks are safer than
>Cotter less cranks. This is my opinion only, it is not based on
>statistics or anecdotal evidence, just my recollection of some distant
>history.
>Thomas Witkop
>Rockville, Maryland
>On Mon, 09 Jul 2001 16:52:50 -0700 "Meyer Lenore"
><lenoremeyer@hotmail.com> writes:
>> There was a thread a short time ago on cranks rupturing. I do a fair
>> bit of
>> riding on some vintage British cottered cranks and I'd like to know
>> if there
>> are any safety issues in using them.
>>
>> Are cottered cranks inherently weaker or stronger than cottered
>> cranks?
>>
>> Does the fact that some I ride on are 50 years old pose a problem?

>>

>>

>> M