Seatpost creaking in frame (and ideal insertion)

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Alexandrumarian
Posts: 795
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

Got a new light carbon frame. Seat tube is both wide and highly flexible. I get intermittent creaks no matter how tight i do the clamp (well i didn't go past 5nm). I tried two posts, two clamps and from no paste to as much as i could squeeze in. No it is not rails, rail clamp or anything else. It is not wide enough to allow metal shimming (coke can etc) so i will try to widen the post with a superglue coat, and if that fails, a thicker coat of epoxy mixed with CF dust.

I am wondering about insertion in the context of a flexible tube (and very heavy rider). Wouldn't it be safer for the tube if the seatpost extends as little as safe below the lower end of the toptube? Say about 4-5cm. I currently have 13 (weight saving not included in discussion)
Last edited by Alexandrumarian on Mon Sep 25, 2017 6:09 am, edited 1 time in total.

by Weenie


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sungod
Posts: 1702
Joined: Fri Dec 24, 2010 9:37 pm

by sungod

if it really is the post, my experience is that a creak means it has slipped very very slightly, just a fraction of a mm, too small to notice by eye

post and frame will both have minimum insertion limits

for the frame i think the usual rule of thumb is for the post to extend down at least to the lower end of where the seat stays join the seat tube, in practice it's usually going to go further

fwiw i found a mix of both tacx (pink, fine grained) and finish line (clear, gritty) pastes was more effective than either on it's own

Alexandrumarian
Posts: 795
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

Definitely post. For example, saddle and saddle clamp removed, toptube clamped between legs, rocking seatpost by hand creaks. Only sideways, not along the bike. At 2Nm it does it badly, at 3 so so, at 5 nothing but happens on the road. Strangely i built the bike, did 3Nm and went for a mountains vacation, had no creaks for 200km. Got back and it was doing it. Didn't notice the saddle hitting sime branch or bird while on the car :)

The paste i have is morgan blue, seems super low grit unfortunately.

Thing is the unclamped fit seems too loose to be right. I am concerned with what it does down below and with constant leveraging on the part above the seatstays...

TheKaiser
Posts: 653
Joined: Thu Sep 05, 2013 3:29 pm

by TheKaiser

Alexandrumarian wrote:Got a new lightweight carbon frame. Seat tube is both wide and highly flexible. I get intermittent creaks no matter how tight i do the clamp


Is this a carbon frame that has low weight, or is it actually a "Lightweight" brand frame? If it isn't Lightweight brand, what kind of frame is it, and what kind of seatpost?

Alexandrumarian
Posts: 795
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

Edited to avoid confusions with the brand.

I didn't put names as I don't want it to be a bashing thread, I am very happy with the road feel and the rest of the build (for example bottom bracket cups pressed in in a very satisfying way, not too easily, not struggling, no weird noises when doing it, no creaks on the road)

It is possible they choose to ream a bit wide to avoid situations where an oversize seatpost (say 27.3) would have to be hammered in (or at least seize later) but still they kind of went too far. The posts I tried were exactly 27.2 with a vernier and they rattle a bit in the hole when unclamped. My plan is to widen the post then sand it until i get a perfect slip-fit along the entire insertion.

Googling shows it seems to be a fairly common problem both from wide frames or undersized posts. Even found a guy who declared his creaking stopped after cutting the post shorter. For unknown reasons I have a mental blockage in shortening mine. But by logic I feel the more it extends down, the more it can lever/push in the seat-tube when hitting a hole hard or simply being yanked by saddle movement under heavy pedaling.

robertbb
Posts: 2179
Joined: Thu Jul 23, 2009 3:35 am

by robertbb

Would be very interested to know the brand (feel free to PM if you don't want to make that public).

I had a similar issue with a very well known and expensive composites manufacturer, and turns out when measured with a digital ruler the post was 27.0 at certain points (meant to be 27.2). I really had to fight them, but eventually they agreed to refund.

Alexandrumarian
Posts: 795
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

No problem, it is a new Simplon Pavo 3. I am not bashing - I actually tried to film how it wiggles but it is not noticeable. But to explain again, it just fells in with no effort and you can feel it moving a bit inside. I think the part above the toptobe is widest. In contrast in my aluminium Canyon it goes in without play and if well greased, it needs to be rotated a bit to lower in.

Probably in most cases paste and well tightened clamp works without creaks but here some very slight surface feature plus my pork weight makes it happen. The creak is not from the post slipping down but from left and right torque as the feet push down. I can sometimes replicate this by flexing the post with the hand.

Today I will cut a bit from the length and do the glue coat then report back.

Alexandrumarian
Posts: 795
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

And with the risk of totally embarrassing myself. It seems the old vernier I have in my garage is simply worn. Brought in a newer caliper from my workshop and found the seatpost (Canyon S23) to vary from 26.95 to 27.1mm. Took another from a neighbour, same. So old caliper goes to the bin. The frame entry measures 27.25 but it also seems to be slightly curled in probably from the clamp forming it. If it flares a bit further down and with the narrow post, it well explains why it comes to wiggle inside easily.

Just ordered a new seatpost (Ritchey superlogic) - will report back tomorrow when I get it.

GothicCastle
Posts: 304
Joined: Mon Jul 04, 2016 1:52 am

by GothicCastle

I had a persistent issue with a Parlee creaking. It turns out that the seatpost diameter was just a bit small. Swapping for another post with a bit of carbon paste solved the creak.

Alexandrumarian
Posts: 795
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

If anyone was curious about further development.

New seatpost took a while to arrive so I kept riding the old one, without performing any enlargement. The creak went away by itself. Probably very sensitive to something small and hard to detect.

Ritchey superlogic 1 bolt post came and unfortunately it is exactly like the Canyon: only 27mm wide. In terms of weight, 148 (as advertised) and 155 with the larger clamp for Fizik carbon rails. I really like the post because the reasonably low weight is achieved by using less metal in the clamp system rather than using a ridiculously thin carbon tube. Considering my heavy weight, it is reassuring. The clamping system is not easy to set and alter but seems to be bombproof once tightened.

I installed the post this time with a thicker paste (Canyon pink) and it is creak free so far. At some point I will still perform the enlargement as I do not like knowing it moves inside and levers on the seattube at every road bump...

by Weenie


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