When Michelle, my 1991 Bridgestone MB-3, entered my life, I was 1.82 m. In 1995, I hit 1.84 m and her seatpost was max-ed out. Needless to say, when I grew* to 1.87 m, the saddle became too low for anything but short jaunts.
Below the insertion mark on SR seatposts (and Sakae posts) is a stamped mark, such as F-84. The number is the year of manufacture and the letter appears to be the month of manufacture. In the example, the "F" indicates the sixth month, or June.(Vintage Trek)
In this case, "C-90" indicates that my SR seatpost was manufactured in March, 1990. SR Sakae is now known as SR Suntour.
We have discovered that there are two types of measurements used in measuring a seatpost length, the manufacturers, and reality.(BikePro)
Left: OEM silver Sakae Ringyo setback seatpost, 27.0 mm diameter, 310 mm length.
Right: Kalloy black setback 26.8 mm diameter, 400 mm length.
Many soft drink cans measure 0.2 mm in wall thickness. A shim made from one would make up for the 0.2 mm difference in diameter between the 2 seatposts. Personally, I prefer the longer cans.
This is the hardest part of the operation; pay attention:
Pour into a cold glass.
Use a pair of straight (yellow) aviation shears to trim the can to fit. Sheet metal can be sharp, don a pair of leather gloves. Measure twice — make it thrice — cut once. With several (or more) trim and fit cycles, you will eventually arrive at the right sized shim for the seatpost.
Tip: for added insurance, drink a second can so that you'll have a backup in case you mess up. After you empty the second can, you may reckon while you're at it, it may not be such a bad idea to trim your nostril hair with the metal shears. Don't do it.
Seatpost installed with shim.
A closer look. The fit is snug. The seatbinder quick release doesn't need to be tightened much. Distance from Bottom Bracket (BB) center to top of saddle: 79.5 cm.
* = Something that me and my 6' 4.5" (1.94 m) ex-housemate noticed: obnoxious pricks who dish out the phrase "grow up" are always physically shorter than us. Some twisted kind of unconscious longing on their part, coupled with (recurring) episodes of psychotic projection, perhaps?
Hey, look! A gnome!