It's a Thomson 26.8mm in a DMR Trailstar, using an Identiti QR seat clamp. Never used to have this problem but its just started happening a lot. I've not put on any weight (probably lost some if anything) and nothing else has changed. The seatpost gets moved up and down a lot, is it possible that its worn "slick" so it slides in and out too easily?
Any suggestions other than "new bike"?
I've had problems with slipping Thomsons in the past. You could try a new clamp, I use Salsas which look a bit wider than the average. Carbon assembly paste helps too, it's designed to reduce the torque needed to clamp carbon components but it also handy for aluminium.
Just the usual first. Clean and degrease the seatpost and inside of the seattube. If it doesn't help than maybe try a bolt clamp. But best thing would probably be a shim made out of a can, very thin, should stop moving. Also You can try the friction paste.
If all of the above fails than try a bigger post, something like a 27mm or maybe even 27.2 just for size.
[edit] too slow, what he said ^^^ [edit]
I think it's the seat clamp. I have an Identiti clamp on my 456SS and the seat post slipped constantly. There's a plastic shim under the lever and it wears. Tightening the screw just makes it wear faster until it eventually splits. Take out the shim and you'll find it clamps really well.
Will an aluminium post seize in a steel frame without grease? I've got a bit of grease on the post to stop it from doing this but I don't know if thats even possible with alu on steel?
Oh and the plastic shim broke apart years ago, I've been using the same clamp since about 2005-6 and never had any problems with slipping until just recently.
+1 for the carbon assembly paste.
Fixed my slipping seatpost with a slasa clamp. Had that not worked I liked the idea of dusting the post with climbers chalk.
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