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Man, what's with all of the sizes? And do the slight differences REALLY matter?

I'm shopping. I have a frame I'm building up and in looking at seat posts, the sizes are all over the place. I have a 26.8 (pretty certain) in my Schwinn Sting (it's an SDG I-Beam) and it fits right nicely into the new frame. I see a lot of 26.6mm, 26.0, 25.4, some 30.+, etc.

So:
25.4 millimeters = 1 inches
26.0 millimeters = 1.02362205 inches
26.6 millimeters = 1.04724409 inches
26.8 millimeters = 1.05511811 inches

These are obviously VERY close in size... how much should I worry? Or should I NOT?

Thanks.

<blush>

yea, worry about it. Get the proper post to fit the frame.

I hate how the industry has gone like this, but it is what it is. Just part of the price for swapping frames I guess.

Brent-

I can speak first hand of the horror of slight size difference. I just picked up a new Staats frame and went to work that night putting it together. I noticed my post was a little off, no biggie', I thought I am just using it to hold my frame to my stand for assembly. As I put it in, just a bit it started to stick, so I stopped. I hung my frame and went to work putting everything else on. After pulling it of the stand I tried to pull out the post and it was sticking. I twisted just a bit and it felt like it was digging into the frame, OH !@#$ That was it, it was welded to the frame. A costly error, so take your time and get the right post!

Tony-Sounds like your Carma ran over your Dogma!!
I hope you don't sell your ruined frame to anyone....
JS

Thanks for the info... Talked to Heather Allred yesterday too, I can run a 26.6 or 26.8 on the frame I got.

Use the correct size!

You don't want to "crush" the seat tube with the clamp with to small or get one to big stuck. You might could start a 27.0 in a 26.8 frame but you really don't want to do that! Might get it stuck if you go to far and end up galling the ID of the seat tube as well as the post on the way back out.

In a pinch you could shim a one size smaller seatpost up with speedtape. That would be approximately .003 or .004" thick aluminum tape starting with one complete butted 2" wide strip wrap at the bottom of the seatpost and the same up at the seatpost clamp. Add another thickness if necessary. Do not force it in with the speedtape or you might hate life!

Would not leave it in there to long and do this only with one size smaller. Really big corrosion issues if it gets wet alot on a bike rack in the rain. Actually that applies to even the correct size! Lord help you guys who run them through the salt spray!!! Classic potential corrosion cell in there! Aluminum will corrode like crazy under the right conditions. You Staats guys (and others) can be thankful to our Chinese friends who applied a Chromate Conversion Coating (Alodine) to your frames prior to Powder. I see most of the Chinese frames come this way now. Thats the gold color you saw on Spence Prawitt's old Direct Link and inside your seat tube and head tube. Alodine slows/prevents natural corrosion by corroding the metal to begin with. Just some gee-whiz info.

Courtesy of your friendly neighborhood Acft. Sheetmetal guy.

Thanks Dan!