Originally Posted by
busdriver1959
Just a small correction. The 531 seattube is .9/.6. Not .9/.7. The OD is 28.6, subtract 1.2, (.6 x 2). The ID is 27.4. The correctly sized seatpost is .2 smaller. That's how you end up with 27.2.
Only some of the time.
Considering the metric options of .3/1.0, .5/1.0, .7/1.0 and you get lots of options with a 28.0 OD tube, 26.0 OD for the top tube.