Collecting on road data for the gravel wheels was important for several reasons. One, that’s what we do. But more importantly, while finishing the design of our 2016 road wheel line, we noticed that tire size had a large impact on rolling resistance (Crr). It was so great that when considering rolling resistance, the FLO 60 with a wider, less aerodynamic, 25mm tire was faster than the 23 mm tire, which is known to be more aerodynamic. It felt like I had been looking at half the equation for the last six years.
Around the same time, Josh Poertner (CEO at Silca) and Tom Anhault (Engineer, Blather ‘bout Bikes blog), began discussions on impedance and how that affected rolling resistance on road. Rolling resistance was often measured in a lab setting on very smooth rollers. The higher your tire pressure, the lower your Crr value. However, on road is a different story. Roads are not perfectly smooth so if you have a tire with too much pressure, there is a point at which the tires bounce up and down over the small bumps rather than deforming smoothly over them. When these bounces occur, your Crr value increases rapidly and you slow down. The point where the Crr value changes direction is called the impedance break point. Silca demonstrated these break points in a blog article and we have used their image below for reference. We will dive deeper into impedance in an upcoming article.