Session: 02-02-01: Computer-Aided and Simulation Driven Design 1

Paper Number: 165717

Enhancing Racing Bicycle Powertrain Efficiency by Reducing Frictional Losses Through Modified Chain Pitch 

In recent years, the sport of cycling has seen a technological revolution in nearly every facet of sport.  Large strides have been made in the field of aerodynamics as they pertain to cyclists, with clothing, bicycles, and even the riders’ position becoming increasingly optimized.  Advancements in tires have resulted in substantially reduced rolling resistance compared to tires from just a few years ago.  Despite these advancements, bicycle drivetrains have hardly seen any significant improvements. Apart from the addition of another gear every few years, the primary design of the bicycle drivetrain has remained largely unchanged, leaving an opening for substantial improvements in the efficiency of racing bicycles.  This study seeks to evaluate the efficiency of current bicycle drivetrains and improve upon it through the means of system redesign.  This study uses MATLAB for the evaluation of frictional losses of a bicycle drivetrain and ANSYS programs for the drafting and FEA analysis of drivetrain components.

The goal of this study is to evaluate and improve upon the resistance of road bicycle drivetrains.  To achieve this goal, a new drivetrain was designed, MATLAB code was written to calculate the efficiency of the drivetrain, and FEA software was used to confirm the components were strong enough for real world applications.  The primary mode of friction in a bicycle chain is due to the contact force between the roller and bush that is not in line with the axis of tension on the chain (Hollingworth & Hills, 1986).  This force is dependent on the angle between one link and the next, the greater the angle between links, the greater the angle between the contact force of the bush and pin and the direction of tension on the link.  On a bicycle drivetrain, the instance of greatest angle between two links occurs at the cog, as this is the smallest radius curve the chain must overcome.  To reduce this angle, a shortened pitch drivetrain is proposed, the radius of all cogs and chainrings remained as close as possible to current designs. However, the decrease in pitch length resulted in an increase in tooth count for the same radius cog and chainring.  This increased tooth count reduced the angle between each link reducing the angle between the roller bush contact and the tension on the link. However, a very short pitch would result in very small components that would most likely fail. Hence there is need to optimize the design and verification through a finite element analysis.

Our analysis showed that the experimental 10mm chain pitch drivetrain displays substantial advantages over the standard 12.7mm pitch drivetrain, increasing the efficiency by 0.5% to 1.6% over standard 12.7mm pitch drivetrains.  This accounts for up to 5 watts saved over a Shimano drivetrain and 7 watts saved over a Sram drivetrain at the industry standard measurement of 400 watts.  With recent advancements in bicycle technology aimed at saving 1-2 watts, this improvement is more than substantial enough to merit further investigation.  While the experimental 10mm drivetrain is not as strong as the industry standard 12.7mm drivetrain, it far exceeds the strength of a 12.7mm pitch MTB drivetrain and can safely be used in a road bike application.

Presenting Author: Sohel Anwar Purdue University in Indianapolis

Presenting Author Biography: Dr. Sohel Anwar is a Full Professor in the Department of Mechanical and Energy Engineering (MEE) at Purdue School of Engineering and Tech, IUPUI, Indianapolis, IN, USA. He is also the director of Mechatronics and Autonomous Research Lab (MARL). He has over 28 years of combined academic and industry R & D experience in the general area of mechatronics, automation, and controls. His research program is focused on Hybrid and Electric vehicle powertrain control and optimization, Li-Ion battery diagnostics / prognostics / fast charging control, Autonomous vehicle simulation and control, novel sensor development and fusion, and smart novel medical devices. Professor Anwar has published more than 170 peer-reviewed journal, conference papers, book chapters, and eBook. He is also an inventor or co-inventor on 15 US patents (with 1 currently pending). He supervised the research work of more than 60 current/former graduate students (12 PhD, 49 MS). Dr. Anwar's research projects have been supported by the grants from the National Science Foundation (NSF), National Institute of Health (NIH), US Army, Department of Energy (DoE), State of Indiana, Cummins Inc., and many other Industry partners. Dr. Anwar earned his PhD in Mechanical Engineering with specialization in Controls from the University of Arizona.

Authors:

Michael Hemmerlin Purdue University in Indianapolis
Sohel Anwar Purdue University in Indianapolis