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Discussion Starter · #1 ·
I want to get a CF seatpost. My alum bike (tandem) came with a 29.8mm alum 350 long seatpost. The seatpost had a min. insertion of 150mm! Now that made me too low. So I bought a aluminum setback 400mm 29.8mm from Wiggle in the UK. But now I'd like to get a CF one. I'm not looking for weight savings, but comfort.

Best I can find is a Wound Up X-Post Carbon 29.8mm at 350mm long. (I have to find out what the min insertion on that is.)

I could also get a 27.2mm 400mm and shim it.

I'm 220 lbs. Most of all the other 350mm long seatposts are ok on the minimum insertion, and at 350mm, a seatpost would be below the top tube weld point, inserted about 3.8 inches and about 1/2 below the lower weld on my frame.

So which would be better, strength wise, for the frame? A shimmed 27.2 400mm length or a exact fitting 29.8mm 350mm which is a little shorter.?

Of course if anyone knows someone who sells a 29.8mm 400mm (or so), let me know.

Thanks
SB.
 

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Discussion Starter · #3 ·
Hi and thanks. A follow up Q? Was it much longer that the length of the shim in the seatpost tube, and did it wobble at all? I'm trying to figure out if the fact that its not the same diameter puts more strain on the frame.
 

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noMAD man
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Me personally and tons of customer bikes at the shop have been running shimmed seatposts for many years, and I haven't seen a shim related problem yet. I've even seen some decent posts bend in a shimmed frame, and neither the frame nor shim was damaged. I've run long travel trail bikes for years, and I like to sit down through some pretty gnarly terrain. Dirt motor enduro racing for long distances probably caused this habit. All my bikes have had 27.2 seatposts in shimmed frames, and I've never had any breakage, slippage, or other issues as a result. I'm a little surprised, actually. I would have thought shims would bring more issues.
 
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