I would like to change the seatpost on my swift to a Biologic Zorin postpump from Dahon. This post comes in a 33.9mm diameter. I remember from some old threads people were swapping out their seatposts, but I also remember somebody having a frame crack from doing this. The xootr site says that the stock seatpost diameter is 32.9, but I thought people were getting away with using 34mm seatposts. Any help/advice would be great.