- How much can you shim a seatpost
I used a 27.2 post in a 30.9 tube for years before I eventually bought a dropper – USE thermoplastic shim with about 90mm in the seat tube, I weigh about 90kg. It did clear the lower weld on the top tube though, and there’s a brace.
I’d be guided by what your frame maker says, they may have a specified minimum insertion. Ooh er etc. It’d be a shame to have to retire a nice post if you didn’t have to, more of a shame if you damage your frame though!Posted 4 months agomartymacSubscriber
I shimmed my surly from (i think) 31.6 down to 27.2 with a USE thermoplastic shim, it has 100mm insertion, which is the same as the minimum insertion for the thomson post.
surly didn’t recommend shimming, but wouldn’t give me an answer on what the minimum insertion was, they just said to follow the post manufacturer guidelines.
bike has been fine so far, i prefer a 27.2 post, as it fits all my other bikes too.Posted 4 months agohols2Member
As above, check the minimum insertion for the frame (not the seatpost). In my experience, 100 mm is fine, as long as the shim extends down to the lower weld on the toptube. My old Giant NRS came from the factory with a 30.9 seattube shimmed down to use a 27.2 post. I’ve run 27.2 Gravity Dropper posts on all my bikes for well over a decade, they’ve mostly had seattubes 30.9 mm or bigger.Posted 4 months ago
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