4

I've already seen this question: Problems with a slipping seatpost

The main difference is that I have an aluminium frameset and a forged alloy seatpost - lightweight clamp.

After every couple hundred miles on my commuter (particularly over rougher surfaces), I've found that the seatpost slides into the frame by about half an inch or so. After the second time I've noticed and readjusted it, I figured it might just be because I have a lightweight clamp. I over-tightened it past the recommended torque, but alas, it happened again. I then tightened it as far as I dared without snapping the bolt, but have now found that it has slipped another half an inch over the last 200 miles or so.

Is there some kind of paste / compound that I could use that, similar to the carbon paste, would prevent this slippage? I asked the manufacturer and my LBS about the carbon paste, but they explained that it may not be a great help, because the carbon paste is "designed to create a small amount of swelling of the carbon" on the surface of the components, thereby improving grip. Well, this is metal on metal, so it's different ... right?

Update: It is not oily / dirty / dusty and it is not old and worn

For completeness, I have this bike: http://www.planetx.co.uk/i/q/CBPXRT58ALRIV22/planet-x-rt-58-alloy-sram-rival-11-road-bike

With this seatpost: http://www.planetx.co.uk/i/q/SPPXSLT3D/planet-x-superlight-team-3d-forged-alloyseatpost

And this clamp: http://www.planetx.co.uk/i/q/SPPXSLT3D/planet-x-superlight-team-3d-forged-alloyseatpost

Any advice other than drilling a hole through it an putting a bold in (I won't really do this) ?

Note: I tried to add a tag to the question for the correct English spelling for ALUMINIUM, but apparently I need more reputation for that. Right ... ;-)

  • On one of my bikes I've just tried (haven't ridden yet) a second seat clamp just round the post, that will sit on top of the seat tube. In my case the bike is old so I've got nothing to lose by doing this (and steel framed so the frame is tougher than the extra clamp). My reasoning was slightly different -- the built-in clamp doesn't play nicely with pinhead bolts and I can't get much torque. – Chris H Feb 11 '16 at 10:16
  • That's a little odd, given that aluminum/aluminum joints have a tendency to "seize" and hence are typically treated with some sort of anti-seize compound. But probably the simplest solution is a worm drive hose clamp on the seat post just above the existing clamp. – Daniel R Hicks Feb 11 '16 at 13:18
  • And two of those links are the same – paparazzo Feb 11 '16 at 13:46
  • If you put the seatpost in the frame with no clamp, how much play is there? Is it possible the tolerances on your frame or post are a bit off and they are mismatched? After the seatpost has slipped, are you finding the clamp bolt still tight, or is it the thing slipping? – Deleted User Feb 11 '16 at 19:17
  • Are you sure you have the right size seatpost for the frame? I had a 26.6 mm post in a frame made for 26.8 mm, and it would do exactly as you describe - okay for a bit but would move over a couple days. Consider using decent vernier calipers to measure both frame ID and seatpost OD. They should be identical. Your links suggest 31.6mm for both. – Criggie Feb 11 '16 at 21:26
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I had an exactly same problem: Ritchey WCS seatpost, Merida frame (both alu alloy) and a lightweight clamp, like in @Frisbee's answer. What I tried:

  1. Beefy clamp with various torque settings. Didn't help at all.
  2. PVC tape. Helped, but didn't last long.
  3. More torque on a lightweight clamp. I snapped it in half with only 6Nm.
  4. Hair spray. To my surprise, it worked and seatpost stopped slipping, creaking and annoying me.

I've switched to a CF seatpost since then, same problem occured, but hair spray come to rescue again. No slipping for months.

3

After trying a chunkier clamp and hairspray, I found this

Clamp did not help much, the hairspray was better, but I was a little concerned about the solvent stuff in the aerosol.

The Liquid Torque has been applied and I have done over 120 miles since, with not even a millimetre of slippage!

Thanks for the other answers ...

enter image description here

1

I would try a beefier clamp

This is your lightweight clamp
enter image description here

This is a beefy clamp
enter image description here

Based on just visual the beefy has more than twice the surface area and it probably spreads the force more evenly. Grease the threads.

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