With respect to human performance and power efficiency, the gear system in typical multi-speed bicycles is often biassed and redundant. A preliminary user survey in this study reveals that the average utilization of each shift for a multi-speed gear system is less than 40%. This study attempts to measure the optimal pedalling rates for given power output levels as well as design the optimal number of gears and the corresponding gear ratios. Heart rate, ratings of perceived exertion and electromyogram of quadriceps femoris for five male subjects are measured at three different power output levels (40, 80 and 120 W) and four different pedalling rate levels (40, 60, 80 and 100 rpm). Various riding conditions including slope gradient and cruising velocity are also converted to the equivalent power output level. The optimal pedalling rates for the given power output are 40 rpm for 40 W power output level, 40 - 60 rpm for 80 and 120 W power output levels. By using a heuristic rule which finds the least number of gears and the most efficient gear ratio under the given physiological condition, a four speed gear system with the ratio of 0.26-0.38,0.38-0.53,0.53-0.7 and 0.7-1.0 is recommended as the most efficient gear system. Based on the optimal gear ratio suggested in this study, an ergonomic gear system using a novel/unique type of planet gear sets (US patent No. 5 378 201) is developed. (A)
Abstract