Clydesdales/Athenas (200+ lb / 91+ kg) - seat post won't stop sliding down

on my mountain bike I can't get the seat post to stay put. any suggestions? It slides slowly down over longer rides, but mountaing biking, every time I stopped I had to pull it back up a few inches. There has to be a better way. anything out there that will hold my seat in place better? I have tightened the quick release so tight that I almost need two hands to close it.

I was having the same issue on my Roadie... LBS ordered a special lube that has a grit to it. Never moved again

I drilled a hole through seatpost and put a small allen key through it....it has not moved since....

I am not sure what I do when I am riding...I have always had problems with seatposts....I will order a Thomson soon to fix the issue for sure....when I got my new frame it came with a setpost and my old Thomson would not fit it.

I have heard good things about the seatpost paste though..I would try it first...

I drilled a hole through seatpost and put a small allen key through it....it has not moved since....

I am not sure what I do when I am riding...I have always had problems with seatposts....I will order a Thomson soon to fix the issue for sure....when I got my new frame it came with a setpost and my old Thomson would not fit it.

I have heard good things about the seatpost paste though..I would try it first...

seatpost paste? do you have a link? I might stop by the LBS, but I think they are closed today

Replace the QR with a 6MM bolt,nut and washers. Get a grade 8 from NAPA or similar and TIGHTEN it DOWN!
Less likely to have your seat stolen too.

This is pretty common, even among non-clydes. It is one of the reasons why many competition riders put a peice of bar or electrical tape on their seat posts such that there is a sliver of room between the bike frame and the tape-edge (1/2 mm or 1/16 inch or so). That way, you can usually catch it sliding down, and adjust it before it starts tearing up the tape.

I had that problem for a year or more before explaining it to bike shop. They got rid of "quick release" and used a standard seat clamp (needs allen wrench to adjust) and I never had a problem after that.

I had the same issue.

First, I replaced the QR and used a standard bolt. Much better but still slipped.
I then sanded off a bit of the post - enough to get a strip of soda can between the post and the frame.
Still slipped!

However, after a cm of slip, the soda can got "bunched up" where the frame starts and it is now holding its present height. Good enough for me :)

I had this problem too.

Using solvent, I cleaned all the lube from the seatpost and (using a rag on a stick) from the inside of the seat tube.

Problem vanished.

But...

I have aluminum frame and aluminum post. Don't try this with dissimilar metals, lest they get welded together.

I had this problem too.

Using solvent, I cleaned all the lube from the seatpost and (using a rag on a stick) from the inside of the seat tube.

Problem vanished.

But...

I have aluminum frame and aluminum post. Don't try this with dissimilar metals, lest they get welded together.

Don't try it with aluminum and aluminum--they WILL gall. There are a few combinations that are worse than Al-Al for galling, but they mostly involve stainless steels.

I had that problem, got solved with a Salsa QR, a lil expensive but worth it. :)

If you have a rear reflector that mounts on the seatpost, move it down to the collar at the top of the seat tube and tighten it. This doubles the clamping surface and also provides an indexing stop for returning the seatpost to its exact position when you take it out for some reason.

Be careful about tightening a sturdier bolt on a carbon seatpost. The post may crack.

*update*

I went into the bike shop, and the guy told me that the problem was simply excessive grease on the seat post, he cleaned it off, and warned me it would squeak a little. well it does squeak, but not so loud that I can hear it over my music (head phones) and I can hear people talking me through my head phones just fine (along with traffic, etc) so I know that it's not terribly loud. its also nice having it stay in one place...

In other news, I went the fastest I have ever gone on flat ground the other day 24.5MPH for about 1/4 of a mile, I was trying to keep up with another cyclist, he was working pretty hard too. but it felt good, and confirmed my fears that I am getting stronger...