Bicycle Mechanics - The seatpost keeps slipping!

My dudefriend has a stock Airbourne Valkyrie and seatpost clamp keeps slipping.

He will adjust it every ride (and tightened it all the way down) and in no time it creeps down 4-5mm.

This is a 350mm post and is 2/3 in the tube. The boy weights between 200 and 190 lbs and does work in a bike shop, but is stymied!

Thanks for your help!


***
handmaiden to the princess and the pea

Things I would check for:
1. Make sure you have the correct size post for your seat tube. see link below
2. A very thin film of lube on a seatpost is good, too much is bad. :mad:
3. Try a different seatpost--maybe one with a anodized black satin finish?

Good luck!

Sheldon Brown's seatpost info (http://www.sheldonbrown.com/gloss_sa-o.html#seatpost)

For others with this problem here are some posts from Airborne's site forums:


http://www.airborne.net/eready/forum/topic.asp?TOPIC_ID=2475&FORUM_ID=24&CAT_ID=10&Topic_Title=Preventing+Seat+Post+Slippage&Forum_Title=General+Questions%2FObservations


Anyone have tips on preventing seat post slippage. I ride a Zepp with a Ti seat collar, I feel like I have it tightly clamped and have never stripped it, but I find it consistently slipping. I weigh 195 lbs and would not think that is too much to handle.


I've had the same problem with a Ti seat collar (the Airborne model with the sharp looking, droplike shaped bolt-side). This model is no longer available on the website I think. I can't speak for the other Ti model, but what I can tell you is that my problems totally disappeared when I started using a Campagnolo aluminium seat collar for my Campy carbon seatpost. It also works great on my Ti seatpost.

Seatpost slippage is such a drag, don't you think. I know I cursed a lot when riding on my brand new Airborne and having a great riding experience, only to have it ruined by a suddenly occurring strange riding position and having to adjust the collar every hour.

not sure if there would be room for this - but if you have a very thin piece of rubber (maybe cut from an old tube) you could wrap that around the post and tighten against that. if the post is too small, that may help to make it a tighter fit.

Tim: there should no room at all for a shim, clearance between post and seat tube is going to be
at most 0.01" and that is generous, it should be a good tight wiggle fit, but not so tight that the post is scored by the insertion. The post should go in by modest torque on the seat with downward pressure. If it is looser than this, something is wrong with the size. Sizing is in 0.2mm increments, though not so
many as there used to be. Steve

Try putting a section of a pop can between the seat post OD and seat clamp ID. take the clamp off then adjust it over the added metal , don't cut yourself.

Assuming that the post is the correct diameter, it is likely that your dudefriend collapsed his seat post by tightening the post clamp too tight.

If this is the case, you will notice that by moving the post either up or down away from the normal position, the seat post is tighter in the clamp.

You probably won't be able to notice the collapsed portion with your naked eye.

A quick fix is to take a slice of aluminum soda-pop can. Fold a lip on one edge and slip the aluminum cola can shim into the post tube hole. The folded lip will hold the shim in position as you slip the seat post into the post tube hole.

You can experiment with different widths of shim material until you get it perfect.

Sounds like seatpost is a wee bit too small for seattube.
Solution: Use a proper sized shim; cheap solution: cut up a pop or beer can, and wrap a piece of it all the way around the seatpost. Should do the trick.