How tight should a seat post bolt be?

[ishaw]

I went out on a ride today, just over 2 hours as it goes. During the course of the ride my seat post slipped down really gradually, and not by a lot, but noticeable by the end.

How tight should the seat post bolt be? I've been wary of going too tight as it's a carbon frame and carbon post so don't want to do any damage?

 

[onegoodbike]

I had this issue and the same concerns. I bought some carbon specific grease with tiny beads in to get a better grip and I do my seat bolt up to 8Nm. This seems to be working for me and nothing's gone crunch so far!.

Matt

 

[tintin40]

I have a phobia concerning this. I paint a small white line with tip-ex so I see if moved. But I still tighten plenty.

 

[02gf74]

8 Nm !!!! 5 Nm is what i see on many seatpost clamps, i do up to 4 Nm without problems and i weigh more than you.

Use carbon paste, stops carbon post reacting with the aluminium in frame (yes, carbon frames have aluminium seat tube insery) and it contains tiny particles that grip the post. (Shouldnt happen in theory as the posts are usually laquered..

To get 4 or 5 Nm you need a torque wrench, it is surprising how tight that is when trying it by hand. With Ti bolt, it approaches the point of elasticity i.e. bolt no longer turns.

Doing it up by hand is extremely difficult, you do it it slips, you undo to lift post but want to do it up more than before but no so much that post or frame is damaged, i couldnt manage it so have a 3/8 in torque wrench. Well worth the 20 odd quid for peace of mind.

 

[onegoodbike]

Yes 8!. Seems fine, clamp has 7Nm on it and I'm a bit of a chunk so thought a touch extra probably wouldn't hurt!. This was last year and the post hasn't moved (I too have a line marked on the post) and the clamp hasn't snapped so I guess all is well.

 

[Harryburgundy]

Re:

I would use carbon paste too...made the difference to me

 

[ishaw]

Re:

Well I've set the torque wrench to 4nm and haven't got anywhere near that but it's tighter than it was before. I'm riding again next weds so will report back if this has done the job or if carbon paste is needed.

 

[02gf74]

Re 8nm, is this carbon post in carbon frame?

My carbon frame spesh epic had 5.2 nm etched on tbe clamp, and also have a tippex type pen for marking posts and saddle rail/ clamp,

 

[onegoodbike]

Re:

...it's an alloy post in a carbon frame, I've checked the trek torque spec sheet I looked up last year it states 6.8 - 9Nm.

 

[Twister]

Re:

In the past I've found that changing grease helped

Lithium grease being thicker than what I'd used before.

Carbon paste makes a huge difference though.