A Study on the Efficiency of Bicycle Hub Gears

This study experimentally measured the efficiency of new generation bicycle hub gears. Since efficiency of bicycle drivetrains can be very close to 100% and vary by small amounts between gears bias errors and measurement accuracy must be identified and controlled. For this study an ergometer frame was altered to support research test equipment. A 1 HP motor and gearbox were used to drive the crankshaft. The hubs were attached directly to the steel flywheel using shortened bicycle spokes, eliminating extra chains or drive components. This setup minimizes measurement uncertainty in the drivetrain. Force-transducers were used to measure the motor and flywheel torque, and two magnetic reed switches were used to measure the speed of the motor and flywheel. Efficiency for each individual gear in each hub was calculated for 14 different power speed combinations. The efficiency of each gear was plotted against flywheel Torque, and an exponential model was fit to the data. This model accounts for known variations in efficiency with power and speed, and provides insight into the torque-speed-efficiency relationship. Four internally-geared hubs were measured and compared with a single speed direct drive train and a belt drive. The internal planetary gear hubs measured were the Shimano Alfine 11, Rohloff 500/14 Speedhub, SRAM Dual-Drive, and the Sturmey Archer X-RK8(W). In addition a single-speed direct chain drive, a single-speed belt drive, and a 7-speed derailleur system were measured. The efficiency of the Shimano Alfine ranged from 90.4% to 96.6%. The efficiency of the Rohloff speed hub ranged from 95.8% to 99.5%. The efficiency of the Sturmey Archer hub ranged from 84.6% to 99.8%. The efficiency of the single speed chain drive was found to be 99.71% and the belt drive 98.0%. The efficiency of the 7-speed derailleur ranged from 97.7% to 99.4%. These values found for efficiency are comparable to other studies.