I'd like to fit a suspension seatpost but have only 9 cm between saddle and frame - is this enough?
As Daniel R Hicks says, it depends on the seatpost.
There are some seatposts that offer &quot;passive&quot; suspension—they have no suspension mechanism, and rely on the flexibility engineered into the seatpost's materials (always carbon fiber, AFAICT). From what I've read, these don't do much good. The suspension effect with these will depend on the amount of seatpost sticking out (more material to flex), so even if they do work, they won't work as well for you.
There are a few &quot;active&quot; seatposts that do have suspension mechanisms. Cane Creek has one where the mechanism occupies 70 mm of seatpost length, so that should fit. Redshift sells one that is bang-on at 90 mm maximum insertion depth.