i currently run a thompson 330mm seatpost which has a minimum insertion mark at 60mm up from the bottom.
I run it about 90mm up from the bottom, (so 240mm showing)
the bottom of the post is well below the top tube weld.
looking at (and can get for a good price) a titanium post but it is only 300mm, i reckon this would be just about ok, but would put the bottom 60mm of the tube in the frame with the bottom of the post level with the underneath of the top tube weld.
question is will this be ok?
only do light xc