I have a onone 456 summer season.

27.2 seatpost and 29.8 clamp.

When the seat post is up I have to use less pressure on the clamp to keep it where it is supposed to be than if it is down… What is going on here? New seat post? weird tapered seatpost being the issue? Its not bent as far as I can tell…? weird

edit: not saying the post is tapered.

I would suggest that it is due to the way the post is loaded when in the different positions. When the post is low, you are loading it fairly axially but when it is at full height you are applying more of a bending load on it. The upshot of the bending load is that the post is being forced into the sides of the seattube more and increasing the amount of friction whereas when it is axially loaded it is not getting as much of the frictional help.

no idea on that but my summer season post doesnt go in more than about 6inches …..

i dont need a seat clamp on my seat pin , its wedged in tight.

It could well be that matthew h, but, it doesn’t do it and has never done this on any other bike I have owned..

My post goes in all the way trail_rat…?

edit: not saying the post is tapered.

Have not found many that aren’t in some way tbh

You don’t have much luck with seat posts do you.

Is it a decent post or a cheap one? Anodized or powdercoated?

My first thought was the post is tapered my second was that of matthew_h.

I have no idea what brand the seat post is so probably a cheap one… its anodized though.

I’ll just try another post, already tried another QR that made no difference.

Sounds like a slight taper and probably a bit of wear lower down

I would also go with the possibilities of both.

If you have some calipers then measure the post diameter at different heights to rule out tapering. Failing that it could well be the bending moment of the longer extension.

trail_rat: is that with a 27.2 post? I’ve got a 27.0 Thomson here if that would be any use?

andyl, how long is that thomson post? I keep bending my 27.0s.

I would just do it up enough not to slip?