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Should a carbon seatpost ever have indents from clamping?
Received a new mail-order bike with a damaged seatpost, looked like it had been over-tightened in the frame. Got a replacement and this too made a cracking sound and was left with indents when tightening to below the manufacturers's torque spec. Got a third post and new seat collar but made a trip to the manufacturer's shop to install it and the staff there found the same thing so sent it back. Just had a response from their HQ saying:
"There was no crack to the seat post, and the clamp material is alloy. There is just a slight indent on the seat post from the clamp tightening however this is natural when applying pressure with a harder material, onto a softer material such as carbon. We have smoothed the slit of the seat tube to try and reduce the indent and have torqued this to 6nm for you."
Am I being overly cautious/paranoid but my assumption had always been that other than surface scuffs from sliding in tubes say, that carbon should never have dents or gouges otherwise they run the risk of creating stress risers?
Apologies, don't know how to embed images
https://www.dropbox.com/scl/fi/gjpnzjfk2zmg0fy3smguo/Original-Seatpost-1.png?rlkey=tx8l0exfseca00s83piqwafsw&dl=0 (Original Post)
https://www.dropbox.com/scl/fi/8u62kgq3ortq96rwoo3bq/Replacement-Post-1.png?rlkey=f8ivhn83yc6n2u07n834j9721&dl=0 (1st Replacement Post)
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9 comments
I had exactly the same issue with a kinesis gf ti, ended up ruining three Easton seat posts. The issue was the frame and the seat clamp - I ended up filing the inside of the two sides of the slit in the frame and replacing the seat clamp with a hope one rather than the kinesis one. That may help your issue.
Just collected it this week and that's exactly the end result, it's had the insides of the slit smoothed off and in the meanwhile I bought a Hope clamp as I have an older version on my Kinesis that has served me well. Tested it on the old damaged post first and no marks so should be good to go now.
No, that's very doubtful while proper testing would be fully destructive.
You have to add images via a reply to yourself after the topic is created. One at a time too.
You can add them to the original forum post, but you need to host the images elsewhere (e.g. Imgur) and then provide a direct image link between two "img" tags (i.e. "img" in square brackets at the start of the link and "/img" in square brackets at the end). That also allows you to have multiple images in a post or comment rather than using the easier "Upload" button.
(If you see my earlier post with the two images, you can click on "quote" to see what I mean)
That clamp is clearly not suitable for a carbon post. Many aren't - the ones on some Whytes for example - because they concentrate the pressure on one spot.
It was the 2 edges of the split in the seat tube pushing in. I also e-mailed a carbon repair company and whilst they disagreed with the wording in the response, they said the indentation will likely be due to the resin not fully curing rather than the carbon being damaged which would result in cracking instead if it were so likely is ok but definitely something to keep an eye on or go with a different post so may look to something else instead in the long term.
That doesn't look right to me. It's almost like the clamp is pushing directly on the seatpost rather than pushing the frame onto the seatpost.
Images copied here for convenience:
I've never heard of that happening and have used several carbon seatposts over the years (whether supplied or post-market). I have ridden with someone who's seatpost broke almost halfway into a 60 mile ride, he stayed upright but didn't have a lot of fun on the way home.