I’ve got a Brand X XL dropper. No matter how tight I cinch the seatpost bolt the post drops in the frame. I measured it today, and it dropped 35 mm over the course of an hour and a half ride.
It really feels like the bolt is done up as tight as it can go. Any ideas? The post is the right size for the frame before you ask.

What’s the frame?

My Thomson post used to do that in my Yeti. No matter how tight, and which QR, it would slip down, no twisting just straight down. Carbon paste didn’t help.
Changed it for a RaceFace seatpost and it’s been fine.
Not the best solution in your case!

carbon paste and a double-bolt seat clamp should improve things

My Thomson post used to do that in my Yeti.

Thomsons are usually under-sized which doesn’t help.

Yep, I’d try the “gritty” type of carbon paste.

As asked, what frame out of interest?

Is it worth trying to shim it, even if it’s ostensibly the “right” size?

It’s a Cotic Solaris Max (2020). Not sure how to shim it, there really is no leeway that I can detect.
I’ll pop in to the LBS tomorrow and see if they’ve got carbon paste, or any other solution.

It would have to be pretty loose to get a shim in but it’s possible I guess.

The paste is where I would start though.

Good luck op, annoying issue!

Poss a silly question, but is the clamp fitted correctly?? (bolt across spilt in frame)

How is the fit with the seat clamp off, I’ve had frames were the seat clamp has been hard to get on and the post has held itself up as well as the weight of the saddle without even tightening the bolt but without the seat clamp the post just fell down the seattube with little resistance. I doubt there’s room for a coke can shim so spraying the post with a few coats of clear lacquer could work.

Try a different seat clamp, I’ve had a couple that were crap. Also check the bolt is actually tightening the clamp and isn’t bottoming out on the threads, you could remove it from the frame to tighten it and see if it closes up a bit more.

These look like they might work

https://www.bike24.com/p232618.html?menu=1000,4,327

or
https://clee-cycles.co.uk/P35211/product

I use a bit of plastic pipe, split lengthways and clipped round the post and then held with a couple of zipties. It holds the collar of my dropper at the right height nicely (so far anyway)

What Carlos said.
If you haven’t got the split in the seatclamp in line with the split in the seat tube you’d never get it tight enough to stop it slipping…don’t ask me how I know…

It seems like it’s more likely to be a seat post issue. The previous post was fine (with the same Hope seatpost clamp). The clamp is correctly positioned and if anything overtightened! It says 8nm I think and I tighten it to that, and then a bit more but it still slips.

I’m taking the bike to Sprung in Cinderford for a fork service today, I’ll swing by the LBS on the way home and get then to check it out/buy some carbon paste.

What I generally do is first find the correct saddle height and mark the seatpost where it enters the frame. Then degrease it and lightly sand it to remove the smooth finish around where the clamp is. Then degrease and sand the inside of the seat tube for an inch or two below the clamp. Then smear lots of grease inside the seattube below the point that you have degreased, but keep the top inch or two clean of grease. Then insert the seatpost, twisting it as you push it down to make sure the grease spreads around. Do not insert it beyond the mark you made. This will leave an inch or so at the top that is dry and will grip properly. The grease should stop it from corroding in place. The top inch may seize, but is easy to unstick by gently spreading the slotted section apart.

Use a coke can or beer can as a shim. It does work. Cut it as long as the can is. Don’t over lap it. Wrap it round the post and slip all in together. Try to keep about 1mm sticking out. Roll the top over and clamp as normal. Trust me, it works and will be permanent.

I know you said it is the right size but have you measured the seat post with a digital caliper? Solaris Max is a 31.6 frame isn’t it? I’m wondering if the seatpost was simply put in the wrong box?

“ If you haven’t got the split in the seatclamp in line with the split in the seat tube you’d never get it tight enough to stop it slipping…”

Actually, that’s not true. I was having trouble with a Gravity Dropper post slipping on my old Cotic Soul, and the owner of my LBS reversed the clamp, so seat tube split was at the front but clamp bolt at the back, and it solved it. It keeps the seat tube more circular, less oval, so it grips the post without pinching the sides.

chiefgrooveguru
Free Member
“ If you haven’t got the split in the seatclamp in line with the split in the seat tube you’d never get it tight enough to stop it slipping…”

Actually, that’s not true. I was having trouble with a Gravity Dropper post slipping on my old Cotic Soul, and the owner of my LBS reversed the clamp, so seat tube split was at the front but clamp bolt at the back, and it solved it. It keeps the seat tube more circular, less oval, so it grips the post without pinching the sides.

Anecdotally ive heard that too. Though I suspect you try that way only if the more conventional set-up fails to work first?

I do see an element of logic do it though.👍

I’m sure I’ve seen some manufacturer instructions even advising that, Sam Hill has put the seatclamp facing forward for years despite the seattube slot being at the rear.

I had this issue about six years ago, and guess what, frame was a Cotic Solaris. Internally the seat tube was significantly oversized. So maybe check that’s okay.

Over tightening the clamp isn’t good for the dropper, although some are more sensitive than others. The Fox DOSS I had at the time would bind if too tight.

Otherwise some kind of shim, or friction paste, or that KCNC double height clamp looks like it should do the job. Could possibly cut a second slot in the seat tube for more even pressure. Some Treks used to have three slots.

“Though I suspect you try that way only if the more conventional set-up fails to work first?”

Since then I’ve done it on all my seat clamps – apart from my Levo which has two slots, one on each side and the clamp at the front. Though I guess with that it’s still not clamp matching slot.

We used to shim our BMXs with bits of coke can as it’s really thin

Sam Hill has put the seatclamp facing forward for years despite the seattube slot being at the rear

Me too. I always did it because it keeps the bolt out of direct line of all the mud getting flung up off the back wheel. Also partially covers the slot which makes sense for the same reason.

I’ve never had an issue with any post slipping on any bike that I can think of.

I have a post that slips a little. Hope clamp seems to be doing the trick at the moment, but I have bought one of these on case.
https://www.tredz.co.uk/.XLC-Seat-Clamp-For-DH-Freeride-PC-B04-_126897.htm

Bit cheaper than the kcnc version