Torque on carbon seat post

[avroncotton]

Just got a new Hi-Mod Cannondale Synapse. The seat post was set to the recommended rating of 6n/m. However, riding on Sunday the post slipped all the way down. I had to tighten it with my multi tool and I know I went over the 6 n/m. Has this happened to anyone else and should I be worried about damage from over tightening?

Tony

[Nobody]

Yes.

I was going to suggest a dual (diameter) clamp but it appears the Synapse has some kind of strange shaped seatpost, so probably unavailable for it.

Maybe try some TACX Carbon Assembly Compound (or similar) which provides more friction so you can get it to hold at the specified torque. Another option which I've used successfully (on metal parts) is a non-hardening gasket sealant which you can get from automotive stores.

[jacks1071]

Just got a new Hi-Mod Cannondale Synapse. The seat post was set to the recommended rating of 6n/m. However, riding on Sunday the post slipped all the way down. I had to tighten it with my multi tool and I know I went over the 6 n/m. Has this happened to anyone else and should I be worried about damage from over tightening?

Tony

Pull it out and re-assemble with carbon grease, 6NM is the max tension on many carbon posts (with good reason).

[pawnii]

this is a common problem with the Scott Foil framesets. I wouldn't tighten it any more than the specified maximum torque setting.
Use carbon assembly paste. This helps the seatpost grip the inside of the down tube. It works a treat.
The trick is to coat both the seapost and the inside of the downtube for the full length that the seatpost will sit inside the downtube.
Don't grease the bolt as that'll give you more clamping pressure for the same amount of torque setting on the bolt.

This issue has been driving me nuts for weeks. My seatpost keeps slipping and every time it happens it scratches the seatpost. Over tightening the bolt will crush or crack the frameset.

[Mulger bill]

What he said re assembly paste.

I've damaged a Cf post by overtightening, an almost 1mm deep indent in the exact shape of the top of the seattube/clamp. Needless to say, that post is now lying around the shed getting odd lengths sliced off for the occasional MacGyver, still got about 22 cms left. The thought of having one of them babies shattering under me bum and leaving a jagged pipe cms from the lads is not a pleasent thought.

[pawnii]

This is what can happen when you over torque a Scott Foil.

[L'Aerodynamique]

This is what can happen when you over torque a Scott Foil.

My Foil looks like that although I've had no problems with the seatpost slipping. Do you think I should be worried/ ask for a replacement frame?

[pawnii]

If it's under warranty i'd definitely ask for a replacement.
It's a known manufacturing issue/fault in the carbon lay-up around that area on frames made within a 6month period....so that's what I've been told anyway.

My Foil seat post doesn't slip or creak either but the crack would let water in the seat tube.

It's not something that should stop you riding at all.
It's more if you undo the bolt to move the seatpost, when you tighten it up to the <12Nm max specification, the crack will get larger and larger and you will need to tighten it more and more everytime or your seatpost will slip.