Originally Posted by
SlowRoller
By moving your saddle aft, you are moving the weight of your butt back. This weight will help counter-balance the weight of your upper body, relieving your hands, wrist, arms, shoulders, and neck of this duty. Try this: stand upright and note the position of your behind. Now, bend forward at the waist without moving the position of your butt. The result is you fall forward. On a bike, you support this forward weight with your arms. Next try bending forward and allowing your butt to move backwards. The result is your rear will counter-balance your upper body and you can maintain that bent position without falling forward. That is the dynamic you should try to capture when dealing with your saddle fore/aft position.
Statics tell us that it doesn't work the same on a bike as on one's feet, simply because, when seated, one's weight is on one's butt, not on one's feet. Pedaling properly, there should be almost no weight on the pedals. One should feel as though there were a layer of air between the sole of one's foot and the shoe. Standing of course is another matter, but that's not the subject under discussion. Rather than use some random method of saddle positioning, it's better to use KOPS: drop a plumb bob or other weight from the bony protrusion below one's knee cap, in the front. This should approximately bisect the pedal axle. Using the protrusion in front of the knee adds a little setback that has been found helpful for long distance riders who wish to bring into play more of their leg muscles.
I disagree about the common wisdom of raising the bars and shortening the reach to increase comfort. Look at it this way: You are sitting on your butt. The center of gravity (CG) of your upper body is somewhere in the middle of your torso. Thus a couple (torque) is created. As we know, torque is force X distance. To prevent the torso from dropping around the butt pivot, we must counter this with another torque. Again, force X distance. It's easy to see that if we increase the distance from the butt, the force required is less. Thus more reach reduces, not increases, pressure on the hands.
There is a limit on how much reach is desirable, which will vary with the body proportions and ability of the cyclist. Some elbow bend is always desirable, and the average tourist isn't as thin or muscular as a racing cyclist, so less hip bend is called for. Many long distance cyclists find that for every centimeter the bars are raised, they should be moved forward two centimeters. To see why this might be, bend forward at the waist, putting one's torso at about a 45° angle to the horizontal, the normal long distance position. Put a slight bend in your elbows. Now rotate your arms, pivoting of course at your shoulders. Observe the arc through which your hands move. Lower down, they move mostly forward. If one's bars were at the height of one's shoulders, movement would be entirely upward. At normal bar height, this approximate 2:1 ratio is observed.
This is the reason that one's arms become tired more quickly holding the bar tops than with hands on the hoods, if one maintains the same torso angle. Of course it is also possible to sit almost upright and use high bars and a close reach. This definitely does take the pressure off one's hands, but it greatly increases wind resistance and is much harder on the back, which must then take axial instead of bending loads. Most long distance riders find the 45° torso angle to be a good compromise. Photos of The Position here:
http://www.bikeforums.net/showthread...1#post12207030