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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 10-19-09, 07:23 AM   #1
DanRH
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Slipping Seatpost

Not on my daVinci , on my fixie. OK, I know I should be posting this "over there" but this is like home to me so....

On my steel fixed Lemond, my seat post keeps slipping to a point that is about 27 inches from the center of the BB. I keep moving it up to 28.5" which is my heigth but it keeps slipping. I've re-greased the seat post and have bought a new collar which I thought would do the trick. The seat post is a 27.2. HELP!
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Old 10-19-09, 07:37 AM   #2
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Originally Posted by DanRH View Post
On my steel fixed Lemond, my seat post keeps slipping to a point that is about 27 inches from the center of the BB. I keep moving it up to 28.5" which is my heigth but it keeps slipping. I've re-greased the seat post and have bought a new collar which I thought would do the trick. The seat post is a 27.2. HELP!
Suggestion #1: If something sticks, grease it. If something slips de-grease it.

Suggestion #2: If degreasing doesn't stop the problem find some Tacx Dynamic Paste or FSA's Composite Installation Compound and coat your seat post with that: that will solve the problem. If you have a good bike shop nearby you could probably take you bike in there and see if they'd let you slop on some of their Tacx or FSA compound gratis.

Regardless, if it's just a little lose that should do the trick and a shim shouldn't be necessary. If it's still slipping with the compounds a small shim trimmed from an aluminum soda can might do the trick. I've had a Diet-Coke shim in my Ventana's front seat tube since '02: works just fine. However, I would have preferred that they not over-ream the thing to begin with.
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Old 10-19-09, 07:59 AM   #3
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I've got a Lemond steel single bike with an anodized aluminum seatpost. Though I don't really need to move it, the seatpost is really stuck. I'll trade you some stuck for some slipping and maybe we'll both be happy.
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Old 10-19-09, 08:48 AM   #4
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The slot on the seatpost collar should be on the opposite side of the slot on the frame.
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Old 10-19-09, 09:29 AM   #5
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The slot on the seatpost collar should be on the opposite side of the slot on the frame.
Never heard of this one. Campy instructions on their seatpost are very specific where they should line up.
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Old 10-19-09, 10:07 AM   #6
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The slot on the seatpost collar should be on the opposite side of the slot on the frame.
Never heard of this one. Campy intructions on their seatpost are very specific that they should line up.
This is a spill-over from carbon seat post installation guidelines as a hedge against concentrating the clamping forces on a very small section of the seat post. For alloy and titanium seat posts, it's not a real concern.

The clamping force issue is what brought about stems and seat post collars with slots at 45* angles and the aforementioned carbon / dynamic installation pastes as a way of keeping the torque-wrench impaired from damaging carbon bits.

Last edited by TandemGeek; 10-19-09 at 10:10 AM.
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Old 10-19-09, 10:25 AM   #7
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I've got a Lemond steel single bike with an anodized aluminum seatpost. Though I don't really need to move it, the seatpost is really stuck. I'll trade you some stuck for some slipping and maybe we'll both be happy.
Mine's a Nishiki, but same problem. Sheldon Brown suggests dumping a canister of CO2 in it to chill the Al, causing it to shrink faster than the steel. I haven't tried that one yet - not sure how to dump a canister fast without risking frostbite - or buying a CO2-based pump...
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Old 10-19-09, 10:37 AM   #8
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Originally Posted by mkane77g View Post
The slot on the seatpost collar should be on the opposite side of the slot on the frame.
I'll try that when I get home from my business trip. I have an aluminum seat post BTW. Thanks!
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Old 10-19-09, 03:26 PM   #9
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I'll try that when I get home from my business trip. I have an aluminum seat post BTW. Thanks!
Again, just so you know... flipping the clamp so the opening isn't aligned with the compression slot in a seat post mast will not increase the clamping force.

As previously noted, it prevents excessive "pinching" at the compression slot which can lead to a damaged carbon seat post. Moving the clamp's opening so it sits over a solid section of the seat post even at 90* will reduce the clamping force at the compression slot. Shims used with carbon posts also need to be inserted so their openings don't align with either the mast's compression slot OR the seat post clamp opening. Keeping these slots and openings out of alignment simply distributes the clamping forces so they don't line up where they can do damage to a carbon seat post.

For an alloy or titanium seat post that doesn't compress under clamping forces the way a composite seat post does, having the seat post clamp opening aligned with the compression slot increases the clamping force on the post (which is what you're looking for, more holding power)... but does no harm to the integrity of alloy or titanium seat posts.

By all means, give flipping the clamp around a try. Just understand why seat post mast compression slots were designed to work the way they do both with brazed on seat post clamps (noting the clamp bolt actually pinches the compression slot closed) and with the more cost-effective, non-integrated seat post clamps found on most non-custom, contemporary frames.

A lovely, fillet-brazed seat clamp with compression slot & key hole by Kirk Frameworks before painting.


Last edited by TandemGeek; 10-19-09 at 03:54 PM.
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Old 10-19-09, 04:12 PM   #10
Ritterview
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Not on my daVinci , on my fixie. OK, I know I should be posting this "over there"...
A word of advice for Dan with his slipster.
Discuss your bike here with a synch chain and shifter.





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