Singlespeed & Fixed Gear - seat post stupidity

well, im mm away from finishing my first fixie build, and have realized that my seatpost is waaay toooo long. i have been riding a larger frame, and was thinking i might need more seat extension, but it is a little ridiculous. the thing must go like 200mm into my frame. at least.
anyway, so my understanding is that too long of a seatpost can cause frame bending. no good. my basic question is: is there anything wrong with hack-sawing it into normal 75mm into-frame extension? will cutting it f it up in anyway?
this is the only thing between me and getting on the bike. you know im just gonna ride it too long for a while, but i dont want to mess up my pretty new (used) frame. so ill hack at it unless i hear that it can cause a problem. any thought would be much appreciated.
forgive the mundane-ness and non-fixie specific-ness of the issue. ill be posting pics of it once it have ridden it around a bit

cut it down.
no worries.

too *short* a seatpost can cause frame and ass damage.
i've never head that about a long seatpost though.

cut it if you're worried.

The practice used to be to cut your post down to the minimum length needed, to save weight. The guideline for this was to cut just below the bottom of the top-tube IIRC. I would go at least 1cm below the bottom of the TT inside the frame, to insure stability.

thanks guys, very helpful. ill cut it down in the morning, and leave some room. thanks again.
flexo

can a seatpost that's too long really cause frame damage?

that seems crazy...

doesn't hurt to bevel the edge of the seatpost after you cut it, just to smooth things off.

I'm no physicist, but I have to join in saying that the too-long-post-causes-frame-damage theory seems crazy. Is the idea that if the post goes deep into the frame, it gives you leverage with which to bend the tubes of the frame (by applying your mighty weight to the saddle)? Seems to me that the exposed part of the post would bend and break first. This seems like bostontrevor's area of expertise... trevor?

the too-long-seat-post-causing damage was off of the mechanics forum.
http://www.bikeforums.net/showthread.php?t=9098&highlight=seat+post+length

"An overly long seatpost makes a great lever to bend your frame."
thats my only source

It would seem to me that they are referencing the post being overly long out of the frame.

that makes sense about the too long post. duh.

luckily, i already made it clear in the title of the thread that i am stupid. phew!