Originally Posted by The Hansenator
Ok, thanks. What point is the other end of the measurement taken from?
I dropped a plumb-line from the weight bearing part of the saddle and measured to the BB from there.
It's a good question. In my experience, a centimeter or less can matter, so it would be good to measure to the same point on all saddles. The point that I think is really relevant is where your weight is concentrated, the center of sit-bone contact area.
I agree, it's important to have your center of gravity in the right place, and having your sit-bones hanging off the back is not right, and it is not affected by stem length. Not being able to move the saddle back:
> Saddle rails are located inconveniently -- get different saddle
> Saddle rails too short -- different saddle
> Seat post has insufficient setback -- different seat post
> Seat tube angle is not low enough (Post is too upright) --- different frame with more shallow seat tube.
When you do move the saddle back, lower it perhaps 1/10 of the adjustment distance (you can use trigonometry to calculate it exactly if you remember high-school math). You need to make sure your saddle is not effectively too high after the adjustment.
In other words if you move it back by 1/2 inch, lower the seat post about 1/16 inch deeper into the frame. Use tape to mark it. Lower more (1/16 at a time) if perineal pressure of pain is a problem. Don't go so far that your knees hurt in front.
Once you get this stuff organized, think about reach. You might end up bending deeper with your saddle set farther back, and then you wouldn't need to shorten reach.