Wednesday, June 04, 2008
3TTT seatpost failure
Did it look like it was about to fail? Nope, not at all. I looked and looked again several times at this very component and saw nothing untoward. Did it make any sounds or strange sensations? Well that's harder to answer... maybe. For perhaps 3 or 4 years the bike made a strange creak that seemed to come from the saddle, and the "fix" was to lower the saddle slightly. However I swapped saddles somewhat later and raised the seat height without inducing the creak. So I thought it was indeed saddle-related. Nevertheless it made me nervous and I feared that the carbon frame (with bonded aluminium lugs) was getting "flexy". So I examined it very carefully and could find no cracks or even a creak.
However 50 metres before it broke I felt that the saddle had swung very slightly to one side. Not an especially unusal event as the post can't be over-tightened without cracking the carbon tube. So I slowed to stop but had to get around a corner first... and it was in that corner (at about 25kmh) that 2 things happened. I leaned the bike at a small angle and I put weight on the saddle. (Bear in mind that 1km earlier I had descended at 50kmh and took a hard left hander - seated - at speed without drama.) Anyway, I think now that the crack was invisibly growing from the fluting and gradually circumnavigating the seat post. Only the merest connection remained when I entered that final corner, and I probably rose out of the saddle slightly and knocked the post out of alignment. When I sat down again the crack no longer aligned and simply collapsed under my weight. It took me by surprise and I ended up on the deck.
So the lesson is to expect the unexpected, look at everything for fatigue and don't push aluminium to destruction.. replace it early. And yes, I still use the KG76 today and the frame itself is fine. Touch wood (or carbon).