The magically dropping seatpost

[Deleted member 23692]

No matter how tight I have my seatpost clamp, the seat tends to drop down about an inch from where I set it, on a ride of 10 miles. It's the original seatpost (Easton EA30) that came with the bike (Cube LTD), so I assume it's of the correct size. I've changed the OE clamp as that was a bit notchy, but it's made no difference.

As it's an MTB I'd like to keep a QR clamp so I can easily adjust the seat as and when needed. Anyone have any ideas on how to sort this?

 

[PaulSecteur]

Might be worth trying some fibre grip. Its not a grease, its a paste with rough bits, like grains of sand in.

It is for carbon seatposts in carbon frames where its important not to tighten the clamp too much, the paste with the bits add friction to help this. Cant see why it wouldn't help in your situation.

But I might be wrong.

 

[derrick]

+1
Had the same prob on the cervelo, a small dab of paste and it stays put

 

[Deleted member 23692]

Looks like a trip to the LBS is in order then

Cheers chaps... I (and my right knee) thank you

 

[Shut Up Legs]

No matter how tight I have my seatpost clamp, the seat tends to drop down about an inch from where I set it, on a ride of 10 miles. It's the original seatpost (Easton EA30) that came with the bike (Cube LTD), so I assume it's of the correct size.

I had to get my LBS to replace the seat post on my Vivente tourer soon after I bought it 4.5 years ago, because I had the same problem as you, and it turned out that the seat post wasn't the correct size.

 

[RecordAceFromNew]

Mmmm it seems a current Cube Ltd can have 30.9mm or 31.6mm post depending on which particular model. I would be unhappy if my frame requires a 31.6mm post but was supplied with a 30.9mm, not just because it slipped, but also because alloy does not like being bent very much.

 

[Deleted member 23692]

Just had the verniers out and the seat post is 31.7mm. I've also just stripped all the grease off the post and seat tube - it's a tight fit and quite difficult to move the seat up and down. So I'm happy it's the right size.

I'll try the carbon paste first and failing that, these seem to be 'the remedy' in MTB circles - Salsa Clamp

 

[threefingerjoe]

Here is what may be going on. You mentioned that it's a QR clamp. If you don't get it tight enough, the post will slip. I know you THINK it's tight, and I'll bet you're mashing it with all your might. BUT, if you will put a small bit of grease in the eccentric cam of the quick release clamp, you will be able to get it tighter.

 

[ushills]

+1 for fibre or carbon paste, saves you have to overdo the clamp tightness.

 

[02GF74]

take a look at the clamp ends - I have found that on some non Q/R clamps, as you do them up, the clamp itself starts to bend i.e. the clamp end faces are no longer parllel - meaning the clamp is not getting tighter on the seat tube. The solution I found was to fit a washer in the gap - as the clamp is tightened, the ends will meet the washer so the inner part starts to come together. Obvioulsy the thickness of the washer needs to be selected so that it it thin enough to clamp the seatpost tightly - it also will prevent overtightening = important for CF posts.

Not sure that is explained well, but here is a photo. There is a washer in the gap - the outer part of the clamp ends are up against the washer but if you look carefully, the clamp ends are not parallel as there is a tiny gap between the ends and the washer nearest the seat tube.

 

[Titanium]

If you totally slacken off the seatpost bolt, can you rattle the post from side to side with it about halfway in?
If you can rattle or wobble it, then the post is the wrong size.
Other than that, good suggestions above to look at the collar/clamp - maybe it's worth trying a different one.

 

[Deleted member 23692]

Cheers for the input folks

Here is what may be going on. You mentioned that it's a QR clamp. If you don't get it tight enough, the post will slip. I know you THINK it's tight, and I'll bet you're mashing it with all your might. BUT, if you will put a small bit of grease in the eccentric cam of the quick release clamp, you will be able to get it tighter.

It's already [silicone] greased and 'F-tight'... and yet it still moves. Personally I don't think the lever on the clamp is man enough, especially has the continual slippage has worn the textured anodising mirror smooth.

take a look at the clamp ends - I have found that on some non Q/R clamps, as you do them up, the clamp itself starts to bend i.e. the clamp end faces are no longer parllel - meaning the clamp is not getting tighter on the seat tube. The solution I found was to fit a washer in the gap - as the clamp is tightened, the ends will meet the washer so the inner part starts to come together. Obvioulsy the thickness of the washer needs to be selected so that it it thin enough to clamp the seatpost tightly - it also will prevent overtightening = important for CF posts.

Not sure that is explained well, but here is a photo. There is a washer in the gap - the outer part of the clamp ends are up against the washer but if you look carefully, the clamp ends are not parallel as there is a tiny gap between the ends and the washer nearest the seat tube.

Yep, you explained that perfectly well thanks . I've just checked the gap with verniers and it's perfectly parallel front to back , top to bottom

If you totally slacken off the seatpost bolt, can you rattle the post from side to side with it about halfway in?
If you can rattle or wobble it, then the post is the wrong size.
Other than that, good suggestions above to look at the collar/clamp - maybe it's worth trying a different one.

Tried this test first and it's a very snug fit with no wobble. So it's looking like the clamp, which is the 2nd one I've tried as the OE one was worse the one I'm currently using.

Cheers to all who've suggested the CF compound. I picked up a tube earlier this week but haven't had chance for a test ride yet. Quite an interesting paradox is a grease that increases friction

I've got my eye on one of these at the mo...

..Which seem to be the mother of all clamps, and capable of imparting massive force. Combined with the GF compound it'll hopefully do the trick