Very few use the "commonly used" circular style.
And there you have the explanation for that increased negative work mentioned below. Also unlike the 'Rotor Crank' non round rings have the disadvantage of a double action occurring in each pedalling circle. But even if this negative work is completely eliminated, you still have the problem of having to increase power in a sector where maximal power is already being applied. The sensible way to go is to effectively increase power where the leg is idling.
Previous studies have sought to improve cycling performance by altering various aspects of the pedaling motion using novel
crank–pedal mechanisms and non-circular chainrings. However, most designs have been based on empirical data and very few have
provided significant improvements in cycling performance. The purpose of this study was to use a theoretical framework that included a
detailed musculoskeletal model driven by individual muscle actuators, forward dynamic simulations and design optimization to
determine if cycling performance (i.e., maximal power output) could be improved by optimizing the chainring shape to maximize average
crank power during isokinetic pedaling conditions. The optimization identified a consistent non-circular chainring shape at pedaling
rates of 60, 90 and 120 rpm with an average eccentricity of 1.29 that increased crank power by an average of 2.9% compared to a
conventional circular chainring. The increase in average crank power was the result of the optimal chainrings slowing down the crank
velocity during the downstroke (power phase) to allow muscles to generate power longer and produce more external work. The data also
showed that chainrings with higher eccentricity increased negative muscle work following the power phase due to muscle
activation–deactivation dynamics. Thus, the chainring shape that maximized average crank power balanced these competing demands
by providing enough eccentricity to increase the external work generated by muscles during the power phase while minimizing negative
work during the subsequent recovery phase.
r 2008 Elsevier Ltd. All rights reserved.
Keywords: Forward dynamic simulation; Design optimization; Eccentric chainring; Cycling efficiency . "