Determining If A Bike-mounted Aerodynamic Sensor Can Detect Changes In Wheel Rolling Resistance During Cycling With Different Tire Pressures Outdoors

Abstract

Rolling resistance represents a key resistance force to overcome during cycling. This resistance force is calculated as the product of the coefficient of rolling resistance (Crr) and rider+bike system weight. Crr is influenced by a number of factors including tire pressure. Typically, Crr is measured in a laboratory situation but more recently, bike-mounted instruments have been developed that are mounted on a bike to measure Crr in the field. PURPOSE: To determine if a bike-mounted aerodynamic sensor is able to measure changes in Crr with changes in tire pressure while cycling outdoors. METHODS: A cyclist rode a road bike (combined mass 80.45 kg) equipped with an aerodynamic sensor to measure Crr (Aerolab). The bike-mounted sensor measures a number of parameters such as wind speed, global position system (GPS) data, cycling power, and air temperature, for example. Processing algorithms are used to generate Crr. For this experiment, tire pressure was manipulated in a manner that changes in Crr were expected. Specifically, three tire pressures were tested: 100, 70, and 40 PSI. Tire pressure was measured using a custom made valve system connected to a digital pressure gauge (Ashcroft Digital Gauge, 0.05% terminal point accuracy, 0-200 PSI range). The rider completed 2 trials per pressure condition with each trial consisting of a coast-down test. The rider reached a target velocity and then stopped pedaling. Data were recorded for at least 60 seconds for each trial. The rider maintained the same ride position for each trial. Data were processed using custom software to yield Crr per trial using an iterative algorithm that calculates Crr multiple times using different sections of data with corrections for air temperature. The research team member processing data was not aware of the conditions. Crr values were normalized such that the Crr during the 100 psi condition was set to 100%. RESULTS: Relative Crr values were 100±2.7% at 100 psi, 95.7±1.8% at 70 psi, and 119.6±2.7% at 40 psi. CONCLUSIONS: Using a bike-mounted aerodynamic sensor, changes in rolling resistance were detected when tire pressure was manipulated. However, confounding factors that could influence the calculation of Crr include the influence of subtle changes in rider position, yaw angle, and tire temperature, for example.