Seat posts - that sinking feeling!

[De Sisti]

I tried one of these, but it didn't seem to work (for me).

https://www.sjscycles.co.uk/seat-posts/ ... to-318-mm/

If all else fails you could try the old-fashioned method of using a jubilee clip. Not elegant (to a lot of people), but it works.

[Darkman]

Funnily enough, I've just ordered some of the Park Tool stuff! As I think I said, the inside of the tube did feel slightly gritty so I suspect the bike was originally assembled with something similar.

I may replace the QR clamp too. My saddle is only the standard one but I'd be quite literally buggered if someone stole it.

[DevonDamo]

I've been resisting the urge to contribute this as I know it won't be received well, but I've finally cracked...

The seat on my hybrid started doing the same thing last year - i.e. it seemed to be locked, but during a ride it would work its way down. The seatpost and frame are both ally, and the seatpost had developed a glassy smooth polished surface. I've owned the bike for several years and this was the first time this had happened so I'm assuming I'd either got some grease on the post and/or the surface of the post had become too polished from use.

I'd tried scrupulously cleaning the post, but it still did it. Then a mate told me that toothpaste works in exactly the same way as carbon frame assembly paste. I thought it couldn't hurt to try and.... still working fine to this day after a tiny smear of Colgate.

[Darkman]

You know what? I considered that exact solution myself last night, then thought "nah, don't be so bloody stupid"!

[DevonDamo]

You know what? I considered that exact solution myself last night, then thought "nah, don't be so bloody stupid"!

Haha! The only unknown in my mind is whether it will have any problems in terms of corrosion - I have zero understanding of metallurgy or the PH of toothpaste etc. so I genuinely don't know. Mine's been on there untouched for the best part of a year now so I'll go and check whether my seatpost is now welded-on when I'm next out in the garage and report back...

[Darkman]

At least you shouldn't get bum disea.... sorry, gum disease.

[Darkman]

Um.... 'nother question!

In terms of seat post clamps, what is "stack height"? Looking at a Hope clamp but it says the stack height is 17mm and I don't know what it's on about. Googling hasn't helped.

[Jdsk]

Stack height
Stack height is the distance the post extends above the frame in its lowest position. Differences in seat clamp head design mean some posts are taller (or shorter) than others. The best posts now have very low stack heights, allowing you to fit more travel into a shorter space.

https://enduro-mtb.com/en/the-best-dropper-post/

Jonathan

PS: Found by https://duckduckgo.com/?q=stack+height+seat+post

[DevonDamo]

In terms of seat post clamps, what is "stack height"?

In the context of a seat clamp, as opposed to a dropper post, stack height is just how tall it is. I.e. lay that Hope clamp down flat on a table and it will be 17mm tall

Update on my Colgate assembly paste: just pulled the seatpost out and it slid out like it was greased-up with some proper posh stuff, no sign of corrosion and after all this time it's still minty-fresh. So the toothpaste trick seems to work and might be a useful tip for anyone doing bike maintenance on tour. There are a few applications where assembly paste is advised, e.g. clamping your stem onto your steerer or your bars, especially when there's carbon involved - toothpaste is cheap and readily available.

[fausto99]

At least you shouldn't get bum disea.... sorry, gum disease.

Great tip about using toothpaste!

[rogerzilla]

The best solution is to buy a seatpost that fits better. This may not be the size the bike manufacturer intended or originally supplied, but frames get over-reamed and alu seatposts get smaller if frequently moved or heavily polished (taking the scratches out of a Campag seatpost I had made it a 27.0 rather than a 27.2).

[LollyKat]

On one of my bikes the seatpost tends to slide down a little over the course of a week, even though it feels fast and immovable after I've tightened the bolt (braze-on, not separate clamp). Being afraid of stripping the threads I've now added a sort-of jubilee clip, made from part of a rear light seat-post clamp lined with a piece of inner tube - no more problems . The toothpaste sounds a good idea, though.

[pwa]

What would be really nice would be a protective grease that included fine sandy particles for grip. But I have never seen that for sale.

[DevonDamo]

What would be really nice would be a protective grease that included fine sandy particles for grip. But I have never seen that for sale.

You can get it readily enough, e.g. Fenwicks (https://www.wiggle.co.uk/fenwicks-carbon-assembly-paste) or the aforementioned Park Tools stuff. Although these are marketed for use on carbon components, they still tick both your 'protective grease' and 'fine sandy particles' boxes. My very limited data sample (in-situ for 1 year on one set of ally components) suggests that toothpaste also ticks both those boxes.

[Darkman]

I've just put some of the Park Tool assembly compound on mine, just around the area of the seatpost which sits within the clamp (about 11mm). The rest of the seatpost has a light coat of regular grease to prevent siezing.

Why? The Park Tool stuff is... well, grippy is not the word. I put more on at first, then wiped it off and started again. If you were to put this all the way down your seatpost, I'd suspect that there's no way in hell you'd even get the seat post in, let alone back out again.

It does scratch the seatpost up, as expected, but only on the bit inside the tube where nobody sees it so I don't honestly care.

Only time will tell, but I feel confident it'll do the job.