In search of a smooth pedal stroke: the Bicycle Idler Sprocket Drivetrain Analysis

In the complex world of high-end downhill mountain bike racing technology, every detail matters. That’s why three BCIT Mechanical Engineering students focused their capstone project on mitigating drivetrain issues in high pivot idler bikes.

A high pivot idler is an additional sprocket that helps reduce the pedal kickback effect in the drivetrain. When downhill mountain bikes are traveling at high speeds on rough terrain, riders feel rumblings, pulsations, or roughness from the drivetrain.

Variables of the high pivot idler

The Bicycle Idler Sprocket Drivetrain Analysis team at the BCIT Engineering Expo.
The Bicycle Idler Sprocket Drivetrain Analysis team at the BCIT Engineering Expo

Under the guidance of Stephen McMillan, Mechanical Engineering Program Head, BCIT students Kelly James, Denton Anderson, and Jordan Donaldson created a mathematical simulator that analyzed drivetrain issues. In particular, how changes in the position, size, and tooth geometry of the idler pulley can smooth the pedal stroke.

“Eventually, this downhill mountain bike technology could transfer to other bike applications, like enduro or trail bikes” said Denton, himself an avid mountain biker.

The capstone process

To begin, Kelly, the project lead, plotted the drivetrain points using math. With this information, they used a software program called MATLAB to enter variations in the geometry. This allowed them to analyze how different variations effected the smoothness of the drivetrain. Then they made a physical bench test prototype, with parts supplied by Norco, to test their simulator. This confirmed the results of the analytic models, proving that the simulator is accurate.

Another tool for bike suspension design

“This is one piece of the puzzle,” says Stephen. There are many factors when it comes to suspension design. “If a company like Norco has a design proposal, they can easily run it through the simulation and predict the drivetrain efficiency.” This way they can evaluate the best design options in order to build new prototypes.

Have you subscribed? Sign-up to receive the latest news on BCIT.

Learn more about other capstone projects at BCIT


Leave a comment