I have one each, brand new/ uncut 2015-2017 S5 post.....$250 each

The trick is to torque at 5-10 ft.lbs less that spec and use carbon paste.,,,that worked for me.

Couple quick thoughts, as someone who bought a 2015 S5 with a seatpost that was broken down inside the frame. Basically I follow all of the guidelines in the Cervelo User Manual, which I cannot now find a good original copy of other than some links below:

• carbon fiber assembly paste: definitely; I apply it somewhat liberally to the seat post all around as well as to the face of the clamping wedge that sits against the seatpost.
• clamping wedge: the metal face of the clamping wedge was a little rough and nicked, so I pulled out the entire clamp from the seat frame and used a Dremel tool plus sand paper to clean up the face of the wedge and smooth all other faces out.
• Chamfer: the User Manual calls for a 45 degree chamfer to be cut to the trailing part of the seat post bottom - see here https://www.manualslib.com/...S5-Disc.html?page=33. I'm not a mechanical engineer but what I imagine in my mind that this does is reduce the force acting on one of the longest parts (the end) of the "lever" (if we imagine the seatpost is a lever with the clamping area as the pivot) that's otherwise unsupported internally (b/c the seatpost is hollow).
• The User Manual also specifies that the seat post clamp bolt threads should be greased - which I do. (Many/most Cervelo bolt threads are spec'd to be greased, IIRC?)
• While the manual calls for a max torque of 8Nm I now go slightly below that - both b/c the bolt threads are greased and also b/c of the paste. Last couple times I used 64 in lbs (or roughly 7.2 Nm) - roughly 10% below spec. So far so good, but I'm also only about 146lbs so probably not exerting max force compared to other riders. Maybe I could go lower, which I plan to test next time I move the seat by marking the position with a pencil and seeing if it moves over time. (10% is probably roughly within the error range of my torque wrench, so may not even be low enough to be real).

Here's also a good summary reference with some of this info https://www.bikesnbites.com/...-specs-and-settings/.

Good luck and hope this helps! Others might also have more info, especially through searching or posting in the main forum.

I have one I'll sell you for $100 if you're still searching. It's like the on the right in the picture above. Cut to length roughly 32.7cm from bottom of post to top of post, not including mounting hardware height.

How to make it stay in place: lot of carbon assembly paste. So much that it's hard to get the post into the seat tube even without the seatpost clamp.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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Do you still have either of these posts available?