Seapost slipping when using lightweight seatpost clamp?

Discuss light weight issues concerning mountain bikes & parts.

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02GF74
Posts: 562
Joined: Thu Jan 13, 2011 4:04 pm
Location: Sunny UK

by 02GF74

If you have fitted a lightweight alloy seatpost clamp with a Ti bolt and a carbon fibre seatpost, you may find that even when done up tightly and with carbon paste, the post still slips. :twisted:

You can tighten the bolt further but there is risk of either snapping the bolt, rounding off the hex head, stripping the thread in the clamp, or crushing the seatpost.

Having had this problem, looking at the clamp it is clear that as the clamp is tightened, the clamp ends are getting bent so the gap between then is not longer parallel. The force applied is bending the clamp instead of applying it to the seat tube and post.

To over come this, I have fitted a 0.5 mm washer in the gap so the ends of the clamp are no longer being bent and the force is bringing the ends nearest the seat tube together thus applying it to the seat tube. Obviously the thickness of the washer has to be chosen so that it does not prevent the clamp from being tightened. :thumbup: (it also prevent the clamp from being over tightened)

The photo shows that the gap is almost parallel, there is a slight gap between the washer and the clamp nearest the seat tube - if the washer was not there, then ends furthest away from the seat tube would be would be almost touching.
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maxxevv
Posts: 1949
Joined: Wed Feb 09, 2005 4:51 am

by maxxevv

It sounds counter-intuitive but flip the clamp bolt towards the front of the frame instead if the slit of the frame is at the back. It will allow for a more even distribution of clamping force.

by Weenie


thisisatest
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by thisisatest

Agree that flipping the clamp can help it keep its shape. Doing so usually requires more torque to tighten, so it might be a win/lose. If you do try it, grease between the clamp and frame so one may slide against the other as each respective gap closes.

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yourdaguy
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by yourdaguy

Brilliant!
For certain parts stiffer is more important than lighter.

maxxevv
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by maxxevv

thisisatest wrote:Agree that flipping the clamp can help it keep its shape. Doing so usually requires more torque to tighten, so it might be a win/lose. If you do try it, grease between the clamp and frame so one may slide against the other as each respective gap closes.


Thanks for adding that important bit which I missed out on. :thumbup:

The application of grease between clamp and frame is important. :smartass:

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yourdaguy
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by yourdaguy

I already flip my clamps and put grease "approved by S&S cycles" but I still tend to have problems because if like to use shims to get down to 27.2 so I can use the Cannondale Save seatposts on my mountain bikes. I have been solving the problem by buying Salsa seat clamps which are heavy duty (and turning them around and greasing them with super grease). But this adds another great tool to the toolbox for solving this problem.

Also, I have not been very happy with TACX carbon "grease". It seems to deteriorate rapidly. I have been using never sieze on steel frames with carbon posts, and very small amounts of regular grease with aluminum frames with aluminum shims with carbon posts.
For certain parts stiffer is more important than lighter.

illuminaught
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Joined: Mon Feb 20, 2012 7:56 pm

by illuminaught

maxxevv wrote:It sounds counter-intuitive but flip the clamp bolt towards the front of the frame instead if the slit of the frame is at the back. It will allow for a more even distribution of clamping force.

Very true!
A little bit of carbon assembly compound or a tiny bit of Loctite 609 rubbed on the insider edge could help if the reverse clap doesn't do it.

artray
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Joined: Fri Oct 07, 2011 2:08 pm

by artray

Easy solution ....Just put a little bit of clear coat on your seatpost so it fits tight. Your seat post will not slip and you will not have to tighten your clamp so hard . Works every time .

02GF74
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Location: Sunny UK

by 02GF74

.... actually one of the clamps that I am using with a washer is a Cannondale, which has a little bump so can only be fitted so the gap in the clamp is on the opposite side to the seat tube gap.

I put a small mark with tippex on the seat post then tighten the seatpost bolt by feel whcih may well be less than the recommend setting since I do not have a torque wrench. With Ti bolts you can do them up tight then you can feel the bolt twisting but not actually screwing into the clamp - this is the point where I stop or even back up a fraction; and if the post slips, the washer comes in to save the day.

I am not sure I would like to use the lacquer method since that may help the post sezie in the frame - I had a nightmare time removing a Look carbon post from my Bianchi frame.

artray
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Joined: Fri Oct 07, 2011 2:08 pm

by artray

I use carbon paste as well ....the seatpost comes out fine . Clear coat will not make any difference as seat posts have clear coat on them anyway . I have used this method on my Guru and Trek with no issues .

iamalex
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by iamalex

Useful thread - the more tips the better! Has anyone stopped aluminium posts slipping using the clearcoat trick (specifically a Thomson Masterpiece)?

by Weenie


TheRookie
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by TheRookie

I use carbon grip paste on alloy posts when they are smooth, I also have an ITM which has a recent rough surface so never slips....
Impoverished weight weenie wanna-be!
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