My bikes seat tube is 31.6 and I want to use a post that is 26.8. I'm having a hard time finding a 26.8-31.6 shim but have found a lot of 27.2-31.6 shims. If I go with the 27.2 is it going to be too loose even after I tighten things up?

Thanks for any input.

Outside of Seat Post sizing shim, is Inside of seat tube diameter ..

Outside of seat post is the inside the Seat Post sizing shim,

Get the numbers to match .. If in fact the seat tube is 31.6.. Inside and you get the

31.6-27.2 shim and a 27.2 seat post?


Only, if you Dont use a 27.2 seatpost But insist on using the 26.8...





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Yes, the seatpost is marked 26.8, the manual for my bike says the seat tube is 31.6. The 26.8 seatpost is the one I want to use so I'll just continue to look for a 26.8-31.6 shim. I think I found one on eBay once the seller gets back.

Thanks for your input.

You can Hire a Machine shop and they can custom make one for you, from a bar of Aluminum, on their Lathe.


Kalloy seat posts are cheap , why not just buy a 27.2?

A 1" .. 25.4 is also a common ID for Seat post sizing shims [Wheels & QBP, suppliers to bike shops]

so you can buy a 1" seat post..





Applying Simple Math .... 27.2 - 26.8=0.4 mm difference in diameter .. 2 steps undersize.

shim sheet stock use 1/2 that (radius) so 2mm thick shim stock wrapped around your 26.8 seazt post would bring it out to a measured 27.2, to then use a machined shim in that 27.2/31.6 size..




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