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  1. #1
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    Odd seat post size. What to buy?

    I've got a project bike, that began as a cheap Micargi Triplet Tandem. I'm looking to upgrade the front seat post to a 350mm post, from it's stock 300mm post. I put my digital calipers on the existing post, and it is 28.50mm diameter.

    I've found places that I can buy 28.4mm posts, and 28.6mm posts, but 28.5mm doesn't seem to exist. My guess is that I should buy a 28.6 post, and expect that it would fit based on my "farm logic" that all other female parts measure just under their advertised size, so get the next bigger size. Plus, in a "worst case" scenario, I could probably shave .05mm off the post in a lathe to make it fit, assuming that should hurt the structural integrity much.

    But, from experience, I've learned it is a good idea to post here to see if there is a better solution that my guesswork has found before I start getting out the heavy equipment in the metal shop.

  2. #2
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    typically seat posts only come in a handfull of sizes, however seatpost shims come in just about every size. Buy a 27.2mm post with a shim
    Professional mechanic for 9 years

  3. #3
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    Quote Originally Posted by the sasquach View Post
    typically seat posts only come in a handfull of sizes, however seatpost shims come in just about every size. Buy a 27.2mm post with a shim
    Not an option, since the stoker stem attaches to the seat post and is matched to the size of the current seat posts, which in turn is matched to the size of the stoker's handlebars. I don't want a cascade of replacement parts to deal with changing sizes.

    Like I've said, I've found suppliers for every possible seat post size to the .2mm. I just need to know whether 28.5mm should be ordered as a 28.4 or 28.6.

  4. #4
    Senior Member cnnrmccloskey's Avatar
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    Quote Originally Posted by SvdSinner View Post
    Not an option, since the stoker stem attaches to the seat post and is matched to the size of the current seat posts, which in turn is matched to the size of the stoker's handlebars. I don't want a cascade of replacement parts to deal with changing sizes.

    Like I've said, I've found suppliers for every possible seat post size to the .2mm. I just need to know whether 28.5mm should be ordered as a 28.4 or 28.6.
    seems like it would only be two shims, but If I were you I guess I would go for 28.4 as worst comes to worst shimming is a more legit option than sanding it down if it doesn't fit (at least IMO)
    Quote Originally Posted by Braden1550 View Post
    Monocoque unicycles with internal gear hubs, ridden by extortionists with an excellent sense of balance.

    You'll see. Unless you drilled out your eyes because they were too heavy.

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