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I see Pinarello Dogma and Gan S frames have a proprietary seatpost/seattube combination, which don't have a circular section. An advantage of that design in my opinion is that it's impossible to have the saddle not aligned when adjusting the height of the seatpost. One disadvantage I can see is that if the seatpost is not properly greased and get stuck, you don't have much freedom of movement to leverage on in order to unstuck it. In any case, I was wondering:

Is there any standard for seatposts that don't have a circular section?

Say one wants to build their own frame with this feature. Is it possible to have this on a steel frame? And if it exists, what's the most common standard so that it's easy to find seat tubes and replacement seatpost?

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    CFC seat tubes in CFC frames are much less likely to get stuck, as there is no metal to corrode. – Argenti Apparatus Nov 29 '18 at 17:51
  • @ArgentiApparatus fair, the bikes I was talking are indeed CFC. – Alessandro Cosentino Nov 29 '18 at 19:37
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There has been in the past--Shimano once had aero group variants (Dura Ace AX and 600 AX), which included an aero-section seatpost. I had a bike that came with one such seatpost. Unfortunately the binder clamp on the seat tube didn't quite keep the seatpost in place, and I had to have a framebuilder tap a hole for a setscrew.

  • Nice! I didn't know such areo groupset existed, sweet! What frame was that? Was it specifically build for that groupset? – Alessandro Cosentino Nov 29 '18 at 19:38
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    The frame was from Shogun, and interestingly it was a lugged aero bike (yes, ovalized lugs). I assume it was built to work with that seatpost, it just could have worked better. – Adam Rice Nov 30 '18 at 13:09
  • Are you aware of some history for those groupsets and why they were deprecated? – Alessandro Cosentino Nov 30 '18 at 13:57
  • Not really. The link in my post lets you explore that gruppo in more detail. Shimano was doing all kinds of interesting experimental stuff in the 1970s, but they weren't really raising the bar on quality. With the version of Dura Ace they brought out in the early 80s, they made parts that were more customary looking but functionally innovative (see: SIS), and very high quality and that's what really put them on the map as a pro-level component maker. – Adam Rice Nov 30 '18 at 17:20

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