Any truth to this? i read a few others that said similar thing.the plumb line to me does no make much since either. if your knees are not over the pedal axle would this cause knee problems?
Most fitting "systems" specify that some part of your knee be directly over the pedal axle at some alignment of the crank, usually with the pedal forward and the crank horizontal. This is pure nonsense. Imagine two riders, almost identical, but one rider's knees are 1 inch lower than the other's. In other words, the thigh bones of one rider are 1 inch longer than the other, and his lower legs are 1 inch shorter. Everthing else about these two riders is identical, including overall height, torso length, arm length and weight. If you position the saddle such that the knee is directly over the pedal axle, the rider with the shorter thighs must have his saddle a little under 1 inch further forward of the other rider. It would be exactly 1 inch if his thigh was horizontal at that pedal position, which it isn't likely to be.
But with the saddle positioned forward, the rider with shorter thighs now has more weight that must be supported by his arms, all because of this arbitrary rule about having your knee over the pedal axle. This makes no sense. What matters is your weight distribution fore and aft, and that's determined by the fore-aft position of the saddle relative to the cranks.
This seems like this way makes more sense and more accurate.
After you've determined your saddle height, it's time to position your saddle "fore and aft." You'll notice your saddle has rails beneath it which allow you to position it more forward or rearward. Pruitt again reminds us this fit system is a good starting point, and not a hard and fast rule to position your saddle. Generally speaking, you want the front of your kneecap to fall above the end of the crank arm when it's in the three and nine o'clock position. Sound like Latin?
Take it slow: position your cranks so they rest at three and nine o'clock; that is, they're parallel with the ground. Pruitt says, "I prefer a straight edge, like a meter stick. Take the meter stick straight up from the end of the crankarm (not the pedal, but the rounded point where the crank ends) and it should come to the front of the knee cap (of the front leg), not behind it, not below it." There are a variety of methods of determining your saddle fore-aft, so if you know of a way that works for you, stick with it. Pruitt's is one of the easiest methods I know of, so try his way if you haven't done this before.