New Seatpost Clamp question

[R3awak3n]

I have a seatpost that has been slipping and its driving me crazy. Have tried different seatposts (both carbon), I always use carbon paste and it still slips after a few miles.

I think it might be the seatpost clamp. Seatpost is 27.2 so I thought clamp might be 28.6 but decided to measure and the OD of the tube up top is 29.5 so I bought a 29.8 clamp. Is this correct? I figured its closer to the 29.8 than 28.6.

Ended up going with the wolftooth clamp, has decent reviews so hopefully this will work and end this problem once and for all. (I have had this problem before, thomson clamp and that was so annoying and I will never buy one of those again).

Torque on the clamp is 6nm, don't want to go more because carbon post.

[dem]

I didn't have slipping, but I had a stubborn creak. A really tall clamp fixed it:
http://www.woodmancomponents.com/Web/Product_Show.asp?Sel=PD&CAID=CA20101004142059&CBID=CB20140113164123&PDID=PD20140113165454&Page=1&Lng=EN&Time=2019/4/12%2520%E4%B8%8A%E5%8D%88%252009:13:10

[macaroon]

Yes, a 29.8 clamp will be fine with a 29.5 OD tube.

A few things to consider, how "gritty" is your carbon paste? You could always try grinding up some sand (maybe with a pestle and mortar) and add that to it?

Do you use one of those special "offset" clamps for carbon posts? IME they seem to work better than a normal clamp.

What orientation is the clamp in relation to the slot in the seat tube? There's different schools of thought with regards to this, but I think the clamp slot aligned with the seat tube slot works best.

How tight is 6Nm? I don't use a torque wrench, but I crank my seat clamp up quite tight with a carbon post, I had one carbon post badly scored due to it slipping (make sure there are no sharp edges on the inner edges of your seat tube.

Is your seat post slightly undersized perhaps? Another option would be to give it a few coats of clear laquer to bring it up to size.

[djg21]

I have a seatpost that has been slipping and its driving me crazy. Have tried different seatposts (both carbon), I always use carbon paste and it still slips after a few miles.



I think it might be the seatpost clamp. Seatpost is 27.2 so I thought clamp might be 28.6 but decided to measure and the OD of the tube up top is 29.5 so I bought a 29.8 clamp. Is this correct? I figured its closer to the 29.8 than 28.6.



Ended up going with the wolftooth clamp, has decent reviews so hopefully this will work and end this problem once and for all. (I have had this problem before, thomson clamp and that was so annoying and I will never buy one of those again).



Torque on the clamp is 6nm, don't want to go more because carbon post.



Maybe lose the carbon post and purchase a Thomson. The knurling coupled with carbon paste may end all your problems.

[R3awak3n]

Maybe lose the car on post and purchase a Thomson. The knurling coupled with carbon paste may end all your problems,

I need setback and thomson posts don't have nearly the setback I need to run, and they are ugly (the setback ones). I have carbon posts on all my bikes, its not the posts problem as I never had a problem with a carbon post. Last time I had a problem with the thomson clamp was actually on an alum post.

[R3awak3n]

I didn't have slipping, but I had a stubborn creak. A really tall clamp fixed it:
http://www.woodmancomponents.com/Web/Product_Show.asp?Sel=PD&CAID=CA20101004142059&CBID=CB20140113164123&PDID=PD20140113165454&Page=1&Lng=EN&Time=2019/4/12%2520%E4%B8%8A%E5%8D%88%252009:13:10

I saw those. Maybe if this wolftooth does not work.

Yes, a 29.8 clamp will be fine with a 29.5 OD tube.

A few things to consider, how "gritty" is your carbon paste? You could always try grinding up some sand (maybe with a pestle and mortar) and add that to it?

Do you use one of those special "offset" clamps for carbon posts? IME they seem to work better than a normal clamp.

What orientation is the clamp in relation to the slot in the seat tube? There's different schools of thought with regards to this, but I think the clamp slot aligned with the seat tube slot works best.

How tight is 6Nm? I don't use a torque wrench, but I crank my seat clamp up quite tight with a carbon post, I had one carbon post badly scored due to it slipping (make sure there are no sharp edges on the inner edges of your seat tube.

Is your seat post slightly undersized perhaps? Another option would be to give it a few coats of clear laquer to bring it up to size.

Thanks for the answer. Seatpost is not undersized, I tried 2 of them and they were both perfectly around 27.2.

6nm is not a lot but with carbon 1nm can be fatal. I actually try to keep anything that goes on carbon under 6nm, sometimes 5nm. I tried to find what this ritchey post recommends but nothing about it online. If the post was alloy I would be fine going up to 8nm but carbon I really want to stay under 6nm. On my other 2 bikes I am at 5nm and no slips, no problem which is why it leads me to think its the clamp. you should get a torque wrench :banana:

[ultraman6970]

The campagnolo clamp always worked for me, but at the same time even with aluminum seatpost I put carbon paste in the seatpost and inside of the seat tube.

The other thing that could help is to sand the seatpost with 600 grit, so the carbon paste has more to grab on.

Hope this helps.

[Peter P.]

I need setback and thomson posts don't have nearly the setback I need to run, and they are ugly (the setback ones).

I agree. I won't ride behind anyone with a Thomson setback seatpost due to nausea. ;)

You could try scuffing up the surface of the carbon post, below the minimum insertion line, with sandpaper.

A problem I've seen with some frames is, the seat tube slot is cut too short, not permitting sufficient flex when clamping force is applied to the collar.

My Salsa Ala Carte had this problem and I compared the slot length to a non-problem bike. The difference was between 5-10mm.

I drilled a stress relief hole further down the seat tube aligned with the existing slot, then used a double hacksaw blade (taped together) to lengthen the slot to meet the hole. Worked like a charm.

I see no reason why this couldn't work with any frame material, even carbon.

Also, since larger diameter tubes, especially those with thicker walls, are more resistant to flex, it also stands to reason they would be more resist to seatpost collar compression. You may have to exceed recommended torque specs to achieve sufficient clamping force. My Soulcraft Royale has a 32mm O.D. seat tube with a reduction insert to accept my 27.2mm seatpost. I suffered seatpost slippage until I reasoned that due to the arrangement, I would have to exceed typical recommended torque numbers. Problem solved.

[R3awak3n]

The campagnolo clamp always worked for me, but at the same time even with aluminum seatpost I put carbon paste in the seatpost and inside of the seat tube.

The other thing that could help is to sand the seatpost with 600 grit, so the carbon paste has more to grab on.

Hope this helps.

I thought about that. Some people in another forum were saying chalk works great too.

I agree. I won't ride behind anyone with a Thomson setback seatpost due to nausea. ;)

You could try scuffing up the surface of the carbon post, below the minimum insertion line, with sandpaper.

A problem I've seen with some frames is, the seat tube slot is cut too short, not permitting sufficient flex when clamping force is applied to the collar.

My Salsa Ala Carte had this problem and I compared the slot length to a non-problem bike. The difference was between 5-10mm.

I drilled a stress relief hole further down the seat tube aligned with the existing slot, then used a double hacksaw blade (taped together) to lengthen the slot to meet the hole. Worked like a charm.

I see no reason why this couldn't work with any frame material, even carbon.

That might be the reason but I don't have the balls to drill or saw this frame ahha, that would be a last measure thing. I would get an alloy post and torque the hell out of it before resorting to that.

[ultraman6970]

Put carbon paste as a 1st step, even with the aluminum seatpost.

[R3awak3n]

Put carbon paste as a 1st step, even with the aluminum seatpost.

I always put carbon paste on all my posts. I like to have the least amount of torque and carbon paste really helps with that

[ultraman6970]

Another detail, cant see bike model and brand in question but what if the right diameter is 27.4?

[R3awak3n]

Another detail, cant see bike model and brand in question but what if the right diameter is 27.4?

Seatpost feels pretty snug in there, its def a 27.2. Its a newer cielo, pretty sure they were all 27.2.

[Cicli]

Measure the seatpost. There is a tolerance there. Maybe slightly undersized?
I have a Thomson marked 27.2 that measured 27.1. Went in easy, slipped.

[parallelfish]

I had the same issue with the seatpost collar on my Ridley. Resolved it with a Miche collar along with motorex carbon paste.

http://www.bikewagonmedia.com/media/img/qbp/ST1804.jpg

[Brian Smith]

(snip)I thought clamp might be 28.6 but decided to measure and the OD of the tube up top is 29.5 so I bought a 29.8 clamp. Is this correct? I figured its closer to the 29.8 than 28.6.


Let's make the clamp actually fit the frame.
Apply this stuff either to the inside surface of the clamp or to the outside of the seat tube.
You may be "squandering" a significant portion of the precious 6 N-m of clamp bolt torque simply in deforming the round clamp enough to grab the frame.
https://www.mcmaster.com/1143n22

[ultraman6970]

THat's an interesting product.