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Old 05-26-12, 04:47 AM   #1
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27.2mm to 28.6mm seat post shim

So the correct size seat post for my bike is 28.6 which I must say isn't the easiest size to find. I found a seat post that I really like but it's
27.2mm. Any issues with just purchasing a seat post shim to correct the 1.4mm difference? Will this have any negative effect on the bike?
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Old 05-26-12, 07:48 AM   #2
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Old 05-26-12, 09:14 AM   #3
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28.6mm is a pretty common MTB size.
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Old 05-26-12, 09:25 AM   #4
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If the shim is roughly 3" long, there's be zero mechanical issues with using one. Many bikes have a built in "shim" in that they use an aluminum reducer in the top few inches of the seat tube, so you won't be any worse off.

There is one issue to deal with if you ride in the wet. The shim's full length slot makes a perfect channel for water thrown up by the rear wheel to enter the frame. Be sure your bike has a weep hole in the BB shell (which IMO all bikes need anyway). You might also try to seal the slot with some silicone caulk to prevent water entry. All my bikes are similarly sealed at the seattube slot even though they don't have shims.
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