How much can I tighten a carbon seatpost?

[punkypossum]

Need to adjust saddle hight, but having slight paranoia attacks of ruining the seatpost by overtightening the clamp...not having anything to measure exact torque, is there any rule of thumb??? The lbs said don't do it too tight...which wasn't particularly helpful...

 

[jayce]

you will crush it take it to a lbs ask them to do it then buy a tourque tool better in the long run , or take a chance and tighten small amounts until the seat post will not twist in the down tube

 

[spandex]

It does depend on the seat post, what the bike is made from and the clamp.....

But if you are going to be doing it what you need to do is slowly do up the bolt until it is just holding the post. Then do a 3/4 turn to nip it up but that is a ruff guide and should get near where it needs to be.

What you can do is but a pencil line 10mm up from the clamp just to see if it is moving and if it is just reset the post and do the same thing but go just over 3/4 turn. Then at some point when you are going past a bike shop just pop in and ask if they can check it for you.

 

[mickle]

Tosh and balderdash. Carbon fibre seat-posts may be tightened to exactly the same level as aloonyman posts. Where do people get the idea that carbon fibre composite components are especially fragile?


If in doubt buy a torque wrench and refer to the frame and/or seat-post manufacturer's instructions.

 

[Smokin Joe]

I got a free torque wrench when I subscribed to Cyclesport last year. Using it for the first time recently I set it to the recommended 6nm max for a carbon post. Believe me, I have NEVER clamped an ally or steel post up that tight in my life. I even backed it off to 4nm in the end and it feels about what I would normally do with an Allen key anyway.

 

[punkypossum]

Phew...that's alright then...was getting a bit worried as when I loosened it, it seemed to be more than a 3/4 turn...seatclamp says 9nm, but not sure if there is anything else on the seatpost...

 

[Smokin Joe]

I suspect that instances of broken carbon posts are mostly due to the burrs left on a poorly finished frame cutting through the lacquer and into the material. I use a bit of emery round the edge of the tube and on the inside edge of the clamping slot to smooth them off.

 

[Dave5N]

I'm with Smokin' Joe and Fumefree Mickle on this.

Although I saw a lad (currently National Champion ) nearly disembowel himself last year when a seat post snapped as he leapt on - only truly great bike handling saved him - I have carbon posts in two bikes and just tighten them up as usual. One gets taken out every week and put back in. I have never had any problems.

 

[Steve Austin]

As a staunch member of the anti torque wrench brigade, i would always suggest folk tighten their clamps till it feels tight. If the post slips, then it weren't tight enough, and you need to tighten it a bit more.
If you tighten it until it cracks, then you may need an adult to supervise you when maintaining your own bike.

 

[roadiewill]

I just tighten till tight, without having to put too much pressure in.. by this I mean your hands arent turning red/white

 

[02GF74]

Tosh and balderdash. Carbon fibre seat-posts may be tightened to exactly the same level as aloonyman posts. Where do people get the idea that carbon fibre composite components are especially fragile?

From my experience, I have to disagree. I have never crushed an alloy seat post or even seen the surface marksd.

I have CF post in my bianchi that was slipping (I am not exactly light either!) Doing it up started to mark/crush the post so I stopped doing that as it was still slipping. I solved the problem by inserting a short length of copper pipe to where the clamp was and that solve it - I was able to tighten it without crushing and it has not slipped since.

One thing to note is that ideally you want a wider seat clamp to spread the load over a greater area - I have a narrow one on the Bianchi which is probably not ideal. You can get wider ones - I have just recieved from CR a wider brand-X clamp for a mountain bike (15 mm vs 10 mm).

Having said that, I have antoehr CF post in a mountain bike that did not have this problem - probably wider clamp or thicker post wall?

 

[Blue]

I just tighten till tight, without having to put too much pressure in..QUOTE]

That is what I have always done with carbon - never had a problem.