Influence of Chainring Shape on Cycling Performance

Objective

Previous studies have shown differences between chainring shapes when pedaling, notably comparing the typical circular shape with an oval counterpart. However, most studies have not been able to justify a widespread switch from circular chainrings. The purpose of this study was to replicate previous studies, while further analyzing knee angle moments and forces, to identify if the differences between the two are significant enough to justify a switch to non-circular chainrings.

Approach

Utilizing the VICON system in the biomedical lab at UT Austin, a musculoskeletal model was recreated to analyze the knee angle moments for trials from both elliptical and circular chainrings. Additionally, the use of force-instrumented pedals tracked the force data from the trials, which could be used to gather the total power output. Calibration of both the motion capture system and force instrumented pedals were complex and lengthy processes to ensure accurate readings and mapping of signals.

Data Analysis

The results demonstrated a clear 7.8% increase in efficiency with elliptical chainrings compared to circular ones at an average cadence of 200 rpm. Efficiency peaked at approximately 100 degrees into the crank cycle, where the pedal is nearly parallel to the floor. Notably, the elliptical chainring reduced the effort required during the most intensive part of the cycle, though the circular chainring showed slightly higher efficiency in the later stages due to the less optimal foot path of the elliptical design.

Knee angle analysis revealed no significant differences between the chainring types, suggesting no substantial impact on injury prevention. However, the data confirmed consistent power output readings and provided insights into joint mechanics throughout the crank cycle.

Results

In summary, this study provided compelling evidence supporting the performance benefits of elliptical chainrings compared to conventional circular ones. Through analysis of the force data collection and 3D modeling, an average of 7.8% improvement in efficiency was found, peaking during the optimal point in the pedal cycle. Although the initial hypothesis of benefits in injury prevention or joint strain was inconclusive, the study successfully replicated and advanced research on cycling innovation by utilizing advanced 3D modeling software and force-instrumented pedals to pave the way for future innovations in cycling equipment and design.

Future Improvements

Although the project was extremely successful, with findings that exceeded expectations, a major factor that could affect the generalizability of the research is the limited number of trials conducted. Due to time constraints and restricted access to resources, such as a variety of cycling shoes, only a handful of trials were completed.

A future continuation of this research, planned for the spring of 2025, will include testing at various cadences, increasing the sample size, and potentially incorporating real-world testing to improve generalizability. The scope of the research project was successfully achieved, with accurate force output measurements and motion-tracking software providing robust support for the findings.