Gains from Odd seatpost sizes
 

What is gained when a frame builder settles in on an odd seatpost size (eg. 27.0, 30.0, 29.4, 32.4)?

Or phrased another way; what would be lost if a bikes seat tube were honed and or Permanantly shimmed to be 27.2 or 31.6 only?

Some sizes are so close to being 27.2 or 31.6 that is seems silly not to just make it happen during the design.

Sincerely,
Not happy with the 28.0 post options JOE!

PS - I know there are shims available but they are silly too.

It's not the seatpost, it's the tubing. To keep standard tubing outside diameters (so you don't have the same problem with front shifters, for example), if the tubing wall thickness changes or construction method changes, then the inside diameter is what takes the hit. This is why you tend to have a number of seatpost diameters closely associated -- 26.6, 26.8, 27.0, 27.2, etc. Those reflect increasingly thinner tubings in the seat tube. That's all. Something had to give.

If you are Ernesto Colnago, using a seatpost other than 28.0 means that it is more than likely that people won't buy your overpriced seatpost. :D

Rumors are that FSA is coming out w/a K-Force in 28.0 real soon.
Also, there might be some 28.0 Thomson Masterpieces still around.
Then there are some Italian ones...w/Colnago graphics.