Seatpost slipping down no matter what

[PanoIgano]

I had a bolt in the previous clamp but it broke apart as I tightened the allen bolt. Just noticed it today so I changed back to what the bike came with.

 

[bikeworkshop]

Did you check wobble?

 

[dandy1]

I've had slipping posts with so called 'cheaper' clamps in the past. Moved to hope clamps and that's all I'll run nowadays. No issues since

Also sometimes taking apart, cleaning it thoroughly of dirt, grit, greasing bolt can sometimes help

 

[ishaw]

Have you checked the post diameter Vs seat tube? Tolerances aren't always great on posts and while it may have the right numbers on it, it could be slimmer.

Looks like a yo, 29.4 post right?

 

[Splatter Paint]

I have personally measured seat posts at 0.2mm under-size. I.e. 27.2mm post was actually 27.0mm. A pair of cheap digital vernier calipers would confirm.

 

[Splatter Paint]

Did you check wobble?

This, if the seat post wobbles in the frame or drops rapidly down without the clamp present then you can be pretty sure the post is too small for the frame.

Your average aluminium drinks can is 0.1mm thick. So if you very carefully cut one up and make a shim 100mm long and slightly smaller than the circumference of the post (i.e. it doesn’t wrap all the way round and there is a ~4mm gap) see if you can fit the post in the frame with the shim. If so, the post is definitely too small.

If you push the shim below the top of the seat tube they are a PITA to get out! I normally fold the top of the shim over to stop this happening.

 

[ishaw]

I have personally measured seat posts at 0.2mm under-size. I.e. 27.2mm post was actually 27.0mm. A pair of cheap digital vernier calipers would confirm.

27.0 posts are hard to find, you could have a goldmine there

 

[PhillB]

I had a bolt in the previous clamp but it broke apart as I tightened the allen bolt. Just noticed it today so I changed back to what the bike came with.

I've had a couple of frames with slippy posts in the past, they have always had the 'spring-clamp' seat collar and once I changed them for bolt style collar the problem went away.

I have a Thomson seat collar on my Yo. (sorry not a great picture)

 

[Lhatch4]

You might try using a shim or just get a different seatpost.

 

[al-onestare]

Two pages in and not a single mention of using a Coke can as a shim. This site has gone