Originally Posted by
79pmooney
With lighter steel frames and insufficient seatpost insertion, hard bumps can lead to bulging the seat tube at the end of the post.
Ben
This is what I would be concerned with and the OP's intuition that a longer post is better is correct. The fulcrum is going to be near the binder bolt, so a longer post in the seat tube will spread that force out over a greater internal area.
Originally Posted by
XXLHardrock
The frame is steel. Minimum insertion for the Thompson 29.8 330mm is stated as 63.5mm. So there will be 100mm inserted.
So basically 4 inches. If by "heavy" you mean 250 - 300 lbs, that is probably sufficient.
If you mean 400 lbs, that could possibly damage the frame if you take bump head on without standing and putting some weight on the pedals. A lot depends on how precisely the seat tube is bored.