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Hello all,

My seat post tends to slide down after time and I don't notice it until I realise my legs are not getting the right extension. This happens over days of riding. The clamp states 5nm or torqing but that is no where near enough to keep the seat post from sliding down or my seat twisting to one side or the other. I was thinking of putting another clamp on the seat post to butt up against the top of the seat tube where the normal clamp is.

Anyone else have this drama?

Cheers all
DA

bboy314

First check that you’re using the correct size seat post. What material are the frame and post? If metal, try tightening a little more. A different clamp may help too.

PromptCritical 

I used one of these on the seat tube with a clamp aronud it.

https://www.amazon.com/gp/product/B0...TF8&th=1&psc=1

Jeff Neese

No, never had that problem with a properly-sized seat post. Any chance this one is not original to the bike?

rm -rf

What frame and what seatpost do you have? Post a photo of the clamp, including the frame slot below it.

Years ago, on a previous bike when it was new, the seatpost was slowly creeping downward over time. I assume the force of riding over bumps contributed to this. But I never had the saddle twist sideways, or have the seatpost drop even 10mm. Something doesn't seem right on your bike.

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Years ago, I got a tube of Tacx Carbon Assembly Paste, and still use the same tube now. I like it. It's no longer available.
I see Park Tool has a similar gel, with silica grit. Park Tool Supergrip.

I use it on seatposts and on the handlebar-stem clamping area. It's effective. I don't need the full recommended torque on the stem clamp when I use the gel.
It works for aluminum to aluminum clamping, and carbon to aluminum or carbon to carbon.

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To monitor any seatpost slippage, I used a silver Sharpie pen to draw a line just above the clamp. It will wear off eventually, so I would renew it occasionally. To remove, it, rubbing alcohol easily wipes off the sharpie mark.
Now I use thin 3mm wide strip of masking tape with a slight gap between the tape edge and the clamp. Any slipping is obvious since the gap disappears. (I'm not sure why I keep the tape on the post, since it hasn't moved at all for quite a few years. I did have problems with an older bike, years ago.)

soyabean

I use a bit of SAC-2 which is basically powered quartz that acts as an anti-slip binder.

It's required for all CF seatposts, but can also be used on metal seatposts.

You apply very little of it, exactly where the clamp will contact onto the post.

This is great stuff, I also use it on anything that clamps onto a handlebar. The screws don't have to be as tight and the clamps don't dig into the bar.

Kontact

Aside from the stated correct size post and carbon paste, sometimes posts marked a certain size are not quite the right dimension, causing slip. It is easy to try a different post.

FBinNY 

BEFORE doing anything, take a moment to know what the problem is. This is easy and takes less than a minute.

Eyeball the seat tube (frame) slot. When it was cut, the top was the same width as the bottom. If you have the correct post, it should close very slightly when the clamp is tightened. If it closes more than 1/3rd of its width, the post may be undersized.

While you're back there eyeball the clamp itself. The ears cannot touch each other when it's tight. If they do, that will prevent effective tightening. Assuming the post is right, touching ears call for a new clamp.

Now, if the post is right and the ears don't touch, either tighten a bit more and/or use something to add traction.

Rick

My custom Co-Motion Pangea Rohloff brand new had the seatpost sliding down over time. I had things checked out at a bicycle shop and they claimed that the sizes were correct. I believe it is possible that the Thomson seatpost was flexing under my wight or the mechanics lack of skill and knowledge of tolerance's kept the problem from being solved. I changed to a Nitto 92 seatpost and the appropriate seatpost shim and a Phil Wood seatpost binder. I also tighten the binder bolt between 6 and 7 newton meters. This solved the Problem. The Park assembly grease destroys the anidasion. This doesn't look good at all.

veganbikes

Having used Thomson seat posts on many of my bikes for many years I have had zero problems with them slipping including on a Co-Motion and I am not a light rider at all in any sense. I have to imagine there was a torque issue or they did something wrong in spec'ing the post. My Cascadia is a 27.2 and I have a 27.2 Thompson Elite set back with original clamp zero shims and no slipping ever. I probably used either Park or Phil grease and zero issues there with anodizing. No issues with the anti seize either and any of my posts though my road bike has a Ritchey Classic (as it fit the aesthetics better and I was buying a bunch of stuff from them so it all matched). That seatpost looks like it could be brand new if I did some cleaning on it. I have never had any issues with anodized parts and anti-seize paste and I have 3 titanium bikes and love anodized parts.

Sorry you had issues but I think there is something else at play here. I am glad it is fixed but I would potentially go to a different shop or a different mechanic. Using the proper paste and proper torque and a good seatpost collar you shouldn't have issues unless the frame is buggered. If the anodization is failing then there might be a different issue and it could be the anti seize but I would be doubtful. If it is carbon fiber grip than potentially that could wear off coatings if given the chance to abrade but if properly torqued it shouldn't move at all.

Dark Arrow

I bought the bike new. So it should be correct.

Dark Arrow

Steel frame with aluminium seatpost

Dark Arrow

My frame is Steel and the post is aluminium.

Dark Arrow

I bought this bike new so it is original

Crankycrank

For a steel frame and aluminum seat post with a decently strong clamp you can easily go to 7nm torque and maybe more if you have a feel for its limits. 5nm is usually recommended for carbon fiber frames/posts as they can be damaged easier with too much pressure. Your clamp looks beefy enough but if it's a cheapy it may be made of weaker aluminum.

grumpus

That's a nice bike, a very well thought-out specification. Is the clamp bolt straight, greased and moving smoothly? It should be safe to assume the seatpost is a good fit in the frame ...

mpetry912 

here's what I'd do. draw a line with a sharpie to indicate the post's height that you want

take it out

below the line, use your automatic center punch (or heck even a regular punch with a hammer) and made some "dents" in the seatpost in the range of about 1" below your marked insertion line

doing this will give the clamp some additional "bite".

the other thing you might try is a different seat post clamp. Somebody above mentioned a Phil Wood clamp. Your seatpost clamp puts a bending stress on the bolt as you tighten it. There are some clamps that have essentially a floating nut. These work very well ! The one pictured is $8 on ebay




I have the Stein knurling tool. This works very well too

/markp

FBinNY 

If the clamp is replaceable, and replacements are available, the solution is simple.

Disregard the spec and tighten the clamp enough to do the job. If you cannot turn the bolt tight enough to hold the post securely, check and/or grease the thread and try again.

Save Plan B approaches for when Plan A fails.