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Got a nice Ti seatpost in 27.2mm but my new frame needs 31.6mm
I could get a shim but is it going to end in much frustration and should I therefore get a 31.6mm post?
(yes I know I can try it)
fwiw i don't like shimming cos it puts the stress all at the top of the tube. get a cheap 31.6mm post (or a dropper post..)
I shimmed a 27.2 Syncros post to 30.9 without issue. I used an alloy shim which occasionally cracked and creaked, but a quick clean an re-grease usually silenced.
Plastic shim would prob sort that though (I had a weird size or something I think)
Giant used shimmed 27.2 posts in their frames for years, my new Curtis has a factory shim to drop it to 27.2.
get a reasonably long shim that goes below the TT/seatstay junction on the seat tube and you'll be fine.
chances are that the frame's internally butted anyway 😉
I think it depends on how much you drop the saddle a bit, and how much you ride/do so when its wet/rainy out
If you're a set and forget rider (or at least for that bike) then you're likely getting getting the benefit of the slimmer, likely flexier post with only the possible frame stress worry
If you take your saddle out the frame for storage or transport then Ive found a better than without as the shim tends to stay put where it was, so the shim keeps your ideally pedalling height or whatever for reinserting the post
If you grease the post (carbon friendly grease, eg pace for carbon post) then it helps with putting the post up/down, and as you raise the saddle with one hand hold the shim in the frame with the other it helps with saddle height setting
Ive tried gluing the shim into the frame too to stop it coming out with the seatpost if you'd rather
I remember one particularly wet/rainy ride, where Id dropped the ungreased/crudded up seatpost, but I couldnt pull the shim back down the post to raise the post, as my hands were wet. Since kept on top of any crud/lack of grease on the post
"puts the stress all at the top of the tube"
It does, but they're mostly around 100mm long, which is normally within the minimum seatpost insertion for most posts and frames
Longer would probably be better though as it's spread the load futther for frames that would fit a 200+mm shim
Also got a 27.2mm ti seatpost shimmed into a 31.6mm ti frame - running now for over a year with no problems.
CRC have cheap shims.
I've just bought a 27.2 to 31.6 shim and Tredz were the only people with that size in stock (Crane Creek)when I was looking.