EXPERIMENTAL DETERMINATION OF THE EFFICIENCY OF A MULTI-SPEED BICYCLE TRANSMISSION

The efficiencies of gears in a multi-speed bicycle gearbox transmission were measured and efforts were taken to establish measurement repeatability. Data collected from this apparatus challenges manufacturers to improve their product lines. Given that cyclists are limited in their ability to sustain power supplied through pedaling, minimizing drivetrain losses is very important. Previous researchers have measured various bicycle drives, including chains and belts, multi-speed derailleur sets and multi-speed hub gear transmissions. This study continued to measure the efficiency of a Pinion P1.12 multi speed crank transmission. Repeatability studies were performed using a custom apparatus, capable of providing a wide range of input speed, output power and configuration adjustments and the experiment procedure was adjusted accordingly. Efficiency was evaluated as the ratio of flywheel power to motor power over fourteen combinations of crank speed and output power for each gear. The means and 95% confidence intervals for these efficiencies were calculated, and a nonlinear regression was used to model the data as an exponential function of output torque. The mean of the means was calculated and fit with an exponential curve. Gear efficiency was determined to be the efficiency at infinite output torque, although this theoretical value is only approached at moderate cycling torques. Results indicate these transmissions are comparable to many modern multispeed geared bicycle hubs, ranging from 91.6 - 94.95%. Single-speed and derailleur systems can obtain higher efficiencies. However, the Pinion transmission provides enhanced reliability, reduced maintenance and relocates the majority of the drive weight to the middle of the bicycle. A repeatability study was conducted on the P1.12 transmission.