Looking at it again it does appear that it cracked where the bottom of the seatpost would be. If the shock had done it I would think the crack would be on the other side of the down tube.dogman wrote:longer seatpost would tend to reinforce that area. It looks to me like where the seatpost ends inside the tube. If further down, a second, cut off section of seatpost could reinforce the area from inside some.
Maybe being aware of the problem and never doing drop offs without most my weight on the pedals will make this less likely to occur. I will be using a much lighter setup and I only weight 135 pounds so the stress should be a lot less on the frame.
I think I will also look around and see if I can find a seat tube that will almost bottom out in the down tube to reinforce this area. Couldn't hurt.