skull wrote:Home.
Looks like 6 weeks off the bike to recover and 2 weeks off work at least.
Anyway the seat post in mention was an FSA K-Force with 32mm setback.
http://www.wiggle.co.uk/fsa-k-force-light-carbon-seat-post-2011/I have the same post on my mountain bike, it also had the bolt snap on the seat clamp. Luckily when that happened I didn't have all my weight on the seat so just stood up. Unlike the other day and I was sitting up on the seat.
Thanks for posting details and photos of the seat post.
So it only took failure of one of the two bolts to give you this grief - blows my suggestion that a two post clamp is inherently safer right out of the water. And we need to look for an alternative idea about how not to end up with your troubles.
The set-back design of the post probably puts more bending stress on the front bolt of the clamp, as your whole weight has been moved aft of the post by the set-back. So it might be more likely to fail from the bending fatigue issue suggested in the ekib's post on
Snapped the saddle rail bolt on my seatpost and the post on
Engineering Materials. And with your weight that little bit further back, your chances of avoiding the backside-on-wheel or remains of seat-post aren't looking good.
Can you post an end-on shot of the broken bolt (both sides) like those on the EM post ?
From the photos you've posted so far, it appears the bolt has snapped on the threaded section - was it near the junction between the top and bottom parts of the clamp, or deeper within the seat post ?
I don't know if I'm too naive, but I'd previously thought FSA products were decent quality - it's not like you had a no-name generic chinese clone item. Definitely worth reporting it to them as suggested by the doc's, if only to test how decently they stand behind their products. If they ask you to send the broken bolt to them, maybe get it assessed independently first (and let them know that).
On the more positive side, you've had a good outcome from the surgery and while you're not out of the woods, your fitness will serve you well and help you get through this quickly.
Nobody wrote:Have you considered trying to get stronger bolts? Might be a cheap fix.
If, with all their engineering expertise, FSA didn't get it right, how's skull going to work out just how much stronger a bolt is needed ? The bolt and clamp is a fastening system, and focussing on strengthening just one side of it might not be
such a wonderful idea (e.g. other parts of the clamp could fail).
How does skull decide what will be a "strong enough" bolt if he doesn't have a thorough knowledge of material science and mechanical engineering of such systems ?
FWIW, the problem might have been a manufacturing defect in the bolt - rather than an inherent design weakness. It needs a little more investigation by a materials expert to tell us what the underlying weakness was.
At the moment, I'm glad I've been lazy about trying a set-back seat post as an option to take some load of my forearms (and relieve a little golfers elbow).
Cheers