Another thought exercise on the topic of adding power with one's upper body...
The most efficient way to apply force is in the direction of motion. On a bike, the most efficient way to transfer force from one's leg to the chain is to apply force to the pedal at a right angle to the crank arm, and always in a plane that is parallel to the chainring. However, on a Cruzbike, this would result in pedal-steer. Focusing on the top of the pedal's arc, where the pedaling force is greatest for most people, applying force to the right pedal in a plane parallel to the chainring will push the bottom bracket to the left. To minimize pedal steer, one would need to apply force to the pedal in a plane that passes through headset and the center of the pedal. (Those lucky few who can pedal a Cruzbike no-hands must have learned to do this.)
On my Vendetta, the bottom bracket is about 21 inches in front of the headset, and the center of the pedal is about 4.5 inches outside the center line of the bottom bracket. So at the top of the pedal's arc, the angle between a plane parallel to the chainring and a plane through the headset and the pedal is about 12 degrees. The tangent of 12 degrees is a bit over 2%. If I were able to pedal without any upper-body input, applying force to the pedal in the plane through the headset and the pedal, about 98% of the force applied by my leg would move the pedal in the plane parallel to the chainring, and 2% would be "wasted." If I could push the pedal in the plane parallel to the chainring and use my upper body to perfectly offset the pedal-steer effect, the force applied by my leg would be 2% more effective.
