Mountain Biking - Seat Post - how short is ok?

To those of you out there who do a bit of freeriding, you'll understand the importance of lowering your seat to a point where its out of the way while doing drops/hucks. When I first bought my mtb the seat post was way to high for anything, so I cut it down quite substantially and didn't think much more of it. But lately i've attempted a few more 'technical' drops which require me to position myself right over the back of the bike and i've found that my seat seems to get in the way (I went straight over the handlebars the other day after nosing a landing pretty bad cause i wasn't far enough over the rear). Now I'm thinking that maybe i should cut it down more, but im not sure because i also ride frequently with the seat right up and even now I ride with less post below the clamp ('in' the frame - if that makes sense :o ) than recomended (i think the recommended minimum insertion is about 100mm - but im only a small guy (about 60kg - not sure what that is in lbs) so im not sure if that matters so much. I hope im making sense here. Do you guys think its safe to cut it down more?

In my opinion its not a good idea go below the recommended insertion point at all and especially for freeride/downhill. The simple reason is in the mechanics of the situation. If there is a large amount of seat post in the tube, and you land on it heavy or subject it a strong force, it is most likely that the seatpost will take the damage by either bending or breaking. If there is a small amount of post in the seat tube (ie less than recomended) there is a chance that these same forces may writhe the post out of the frame, bending or breaking the top of the seat tube in the process. In other words its a choice between broken seat post or broken frame. Easy choice.

Some old rules of thumb, regardless of the minimum insertion mark indicated on the seatpost itself, are at least 1" below the top tube junction, or at least 4" total. But the frame manufacturer should be able to give you something definitive.

For instance, I owned a Giant that required a total of 6" of insertion. Specialized, on some bikes, drills a small hole in the backside of their seat tube to indicate how deep the seatpost should be inserted. Both of those examples supercede whatever minimum the seatpost manufacturer recommends.

Like jst wrote, reduced insertion = greater chance of tweaking the post and the frame.

I cut my seatpost to instert at least 2 inches. I make it long enough to extend for pedalling and short enough to insert to the min I need. I have LONG legs so I don't need to slam it into the frame. I usually have a bit showing out of the top. That length for me was 363mm on my dh frame (keep inmind I also had to take into account the broken suspension design, so I couldn't hit the shock) and the standard 440mm works for my ht. :)

someone once said that you can tell a REAL tough guy by the fact that when freeriding he carries his seat and seatpost in his teeth instead of cutting it off. seriously there should be a maximum insertion point( both my bikes have a little spot of welding on the inside, near the bottom, to prevent going too deep) too far out is worse by far but if I remove the welds and insert my post more it will as Mael said interfere with the suspension. 60kg. is 132 pounds. I like your signature BTW