Originally Posted by
fietsbob
answer is C , bottom of the seat post at least in as far as the bottom of where the top tube joins the seat tube..
On my touring bike build I had a classic Campagnolo seatpost I wanted to use, since it was close to max ( because of sloping top tube)
I had a welder add a length of a common Kalloy seat post, that diameter, then get the weld bead machined down smooth..
I really want to see that. That seems like extreme measures but awesome and well worth it.
If you are a larger rider than get the seatpost in farther and get something of length.