Hi, I have attached two photos here. The first shows my seatpost clamp with the sheared bolt. The second shows my spectacular drawing of why it snapped (I don’t have a photo from before it snapped).
I noticed that my clamp bent in this concerning way before, but just ignored it, and then this time I was using my trusty torque wrench to tighten it, and this happened. It’s always been torqued to 5 N-m.
My question is why would this bend like this? Was I missing a piece or doing something wrong? It feels like a design flaw or something. I have other bikes I’ve built up and worked on etc and never had this issue.
Bike is Cannondale Topstone 1 Aluminum btw.
by erand424
6 Comments
Is the seat clamp the correct size? It should be a relatively snugish fit even when there isn’t a bolt installed.
It is an inherent flaw to some designs of clamp – if the screw threads into a barrel nut that can swivel it won’t bend the screw.
https://preview.redd.it/v3imdwf7bo5g1.jpeg?width=810&format=pjpg&auto=webp&s=97dbfb4564a7707c996449781fc0e334ed7bc784
Like this
Is it the original clamp? No possibility of it being too small for the frame?
It could be that the clamp was just shit. Or maybe the clamp was a little undersize and/or the frame a little oversize, so they were a poor fit.
Some bolt-on clamps use a design where the female thread is in a separate, rotating piece. As I understand it, the point is exactly to eliminate a failure like yours: [https://www.bike-components.de/en/Salsa/Lip-Lock-Seatpost-Clamp-with-Bolt-p82013/](https://www.bike-components.de/en/Salsa/Lip-Lock-Seatpost-Clamp-with-Bolt-p82013/)
Get a nice Surly replacement clamp. That one just looks inherently flawed.
5nm torque rated at dry if the bolt was greased is actually 20% or so over torqued if done up to 5nm. normally that’s not enough to snap a bolt. But you can probably find a more robust seat clamp like others have linked. Often times better ones will be rated to 6nm and use a larger bolt than the one you snapped.
even the cheapest one on ali express shouldn’t bent like that if everything is correct, if you find difficult to lock you may need some coke can piece cut up and put inside your seat tube