Sliding Seat post??

Has anyone got advice for how to stop the seat post from sliding down...mine is carbon fibre and other bike has an alloy one?

They are on Mountain bikes.

Try a HALF-shim cut from a soda can, first ... THAT has worked on one seatpost I had which was constantly slipping (a half-shim is alll that would fit in the particular frame) .

On ANOTHER/older frame which I thought was supposed to use a 27.0 seatpost, I finally resorted to a (slightly over-sized?) 27.2 seat post to resolve the problem ... perhaps, 27.2 was the correct size!?!

my salsa seatpost on my giant team once road bike is slididng down too.
the post is a snug fit so there might not be space for a shim or tape there.
the collar bolt is already very tight and tightening it more could snap the bolt or strip the theads.
i could try roughening up the surfaces with sandpaper but that will ruin the nice surface of the seat post. Other suggestions are hairspray or tape but i dont want to use those.
my seatpost is very long, i wonder if cutting it down will solve the sliding problem. the clamp and seat tube might grip the shortened post differently.

some guys at a mountainbike forum solved thier sliding problems by changing to a slasa seat clamp. the seat tube clamp they used is a lot beefier looking than my clamp in the picture and requires no tools to open/close, but it isnt as pretty as my clamp here.

[QUOTE=boffa]Has anyone got advice for how to stop the seat post from sliding down...mine is carbon fibre and other bike has an alloy one?

Do you have to adJust your seat height often or does it stay at one setting?,
if it does,and you have a closed type downtube,slide a wooden dowl stick,into the seatpost and size it into the right height.This will share the load on the locking clamp.Ok so you'll gain a couple of grams but your saddle will stay ay the correct height.

[QUOTE=HowardSteele]now theres a suggestion ive never heard before. Could be worth trying if all else fails. make sure the stick is loose enough to slide out when you want it to.

Since I got my new bikes I do not have those problems anymore.
But one thing I do, I got one of those relectors that clamps to the seat post.
I slid it right to the bottom, it ain't much but seats stay put. Tweenst that and the regular clamp, its good, I lost 35 LBs too, that could help.

[QUOTE=HowardSteele]One leading CF frame maker supplies a little aluminium sleeve for the CF steerer tube and a 2 pack of epoxy, the same method will fix the sliding seat post problem, just like your broom stick.

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Cheers,
George.

I used a piece of pvc once in an emergency

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Trek 7000 ZX
Trek 760