Bicycle Mechanics - Seat post sliding down in the seat tube... Any tips?

Seat post sliding down in the seat tube... Any tips?
Every several miles it goes down inch or so. I'm using QC clamp, cleaned all the old grease from seat post and tube... I can't tight clamp any harder ...
I'm a pretty heavy rider ( 260 or so ) and this bike is used mostly on flat and not bumpy trails.
Years ago, I remember that all seat posts were machined to file like finish. New ones are shiny and "slippery".
I'm using older rockshox suspension seat post with very slippery finish...
Any tips?
Thanks!

You could try this: http://www.universalcycles.com/shopping/product_details.php?id=30551
It contains a gritty component so you don't need as much torque on CF parts to keep them from slipping.
I used it between the head/bar-mount a headlight that wouldn't stop slipping out position and it worked like a charm.

Rough your post with coarse abrasive like 80 grit sandpaper?

Are you certain you have the proper diameter post given
your bicycle's tubing? If this is a replacement post, they
are often sized wrong and will slip.

You could try this: http://www.universalcycles.com/shopping/product_details.php?id=30551
It contains a gritty component so you don't need as much torque on CF parts to keep them from slipping.
I used it between the head/bar-mount a headlight that wouldn't stop slipping out position and it worked like a charm.

I will try it second... Thanks for the link! Looks like it works for other people with the same problem.


Rough your post with coarse abrasive like 80 grit sandpaper?

Are you certain you have the proper diameter post given
your bicycle's tubing? If this is a replacement post, they
are often sized wrong and will slip.

It started happening lately, it's the right diameter. I will try sandpaper on both post and tube first, before trying the paste from previous post.
Thanks guys!

Spray the post with hairspray, let it dry over night and put it in.

grit paste will help, but you shouldn't need it. Take a minute to try to figure out why normal clamping doesn't hold. The first place to check is the clamp collar. Check it for distortion, and see of the backs of the ears touch each other, or if the sides of the slot in the seat tube close until they touch. Also see if the bole has a damaged thread, or if the bolt is bent when tight.

Any of the above, especially the seat tube closing may indicate that the post is undersized for the frame. Or that the clamp collar is damaged.

Spray the post with hairspray, let it dry over night and put it in.
I heard that before...I have to talk to my wife first I guess ;-)
Dzieki! Thanks!

The first place to check is the clamp collar. Check it for distortion, and see of the backs of the ears touch each other, or if the sides of the slot in the seat tube close until they touch. Also see if the bole has a damaged thread, or if the bolt is bent when tight.
Or that the clamp collar is damaged.

Thanks, I'm embarrassed... I didn't even think about checking the clamp itself... Will do it tomorrow morning for sure!

lopek77: If it used to work and doesn't any more I'd carefully examine the clamp for cracking or deformation; a sudden failure could have unpleasant consequences. Be certain that there is a gap at the clamp opening so that the screw is applying tension to clamp the seat tube and not just closing the clamp on itself. You might also try cleaning and greasing the QR threads and cam so that you can easily adjust them. The clamp lever should rotate closed smoothly with steadily increasing pressure. You should adjust the clamp screw so that it takes considerable pressure to close the lever; it should leave a mark on your palm if it is tight enough.

Edit: I see that FB beat me to it while I was typing.

Yes he did dsbrantjr :) I'm glad to hear identical tips...sounds like that may be a problem. I will update this tread when I find out what was wrong, or what works to prevent slipping. Thanks!

I must Assume the seatpost is the right diameter.. not undersized.
A stainless steel band clamp, wont strip as soon as an aluminum one ,
so you can tighten it more
one with a steel barrel nut will also be more tolerant than one
simply threaded directly in aluminum.

It the seatpost is undersized you can try a shim made out of a beer or soda can.

I've used Ironwoods' idea before on a Schwinn Prelude with odd-sized seat tube, and it worked great. I'm just a little north of 260.

I heard that before...I have to talk to my wife first I guess ;-)
Dzieki! Thanks!

Czesc Lopek,

My girlfriend won't let me use her good stuff. I have to settle for her reject can. :) Not that it matters.

I recently had the same problem with a new carbon post. I ended up finding a bunch of advice in some old thread and combined a few of the suggestions. I gently buffed the bottom of the post and the inside of the seat tube with 180 grit. Then I gave it a couple of coats of the hairspray. Let it cure over night, and dusted it with climbers chalk before I put it in. It worked like a charm.

Powodzenia!

1st time i heard about hairspray :) well that thing is pretty sticky and is like a cheap clearcoat, interesting :)

I did over 28 miles last night in 23F weather. Seat post didn't slide down at all...I just adjusted QC clamp. Looks like it was not sitting the right way on the seat tube ( a lot of night rides lately and it was hard to see anything ).
Thanks again for all tips and when I have some more time I will use some sandpaper and hair spray trick to make sure it will never slide down again ;-)