Tuesday, January 09, 2007

Whoops - a case study on aluminium seat post fatigue

My message for the day: if ever you find your saddle pointing slightly off to one side, don't assume that the seatpost is loose and has rotated slightly in the seat tube. It may in fact be about to do something quite a bit more dramatic.

Yes, it was sudden. I had just put my tyre sock on the bike, so I had looked at the offending part. I saw no cracks. I rode just 2kms and went around a big downward curve at 53kmh. After the curve I noticed the saddle was very slightly skewiff. I checked it 3 or 4 times 'on the move' before slowing to round another, sharper curve at about 25kmh. As I rounded it I stood and then accelerated to exit. I was in a mood to keep up the pace today. However when I went to sit on the saddle it simply collapsed. And yes, I managed to fall off and yes, it hurt.

For the record it was a 16 year old 3TTT 25mm post on a Look KG76. I should have kept a closer eye on it, and cleaned it more often, looking for cracks. I knew that aluminium does let go suddenly, and now I can attest that when it splits it does it in a blink, like a knife through butter. High fatigue items with no redundancy (ie single point of failure with no other support) should be on your list of must-checks.

There are more images here, for the curious.

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