Originally Posted by
Nirn
So if the new one's roughly 300 mm with 100 mm beyond insertion point, I should be totally fine.
But then again yeah, maybe longer posts require longer insertion points,
450 mm is a common length for long seat posts. Using that length and the diameter in a search wiill yield plenty of options. If you are still determined to get a new one for this bike I'd go for that length, but mount the seat as far forward as you can.