Part 9 of the Gravel Wheel design journey was a recap of our trip out to Calgary to work with AeroLab. We left Calgary knowing we had a sensor and the ability to measure Crr and CdA on road. We now needed a research team to help us refine the testing protocol and work with the data to solve for Crr and CdA. The University of Nevada, Las Vegas, is right in our backyard and we have connections to two talented cyclists who are an integral part of the Kinesiology and Nutrition Sciences Department. They were eager to help us with our research and the team was formed.
Creating A Partnership
Our On Road Testing Process
After a couple months, we received our version of the sensor. Once we received the sensor, we spent several months refining and testing different protocols to produce good results. The following is a glimpse of our final protocol:
Step 1 - Course Selection
Choose a course with an out and back or loop, with consistent pavement or gravel throughout the test section.
Step 2 - Weather Conditions
Pick consistent weather conditions. Prioritize wind speed and temperature and, if possible, dry conditions. At the beginning of each test, record temperature and wind speed.
Step 3 - Bike Set-Up
The bike set up is key. The following is a list of things that we do for each test:
- Set tire pressure with "the truth" sensor. This has special valves that allows accurate tire pressure.
- Record tire pressure on front and back tires for each run.
- Record tire width for each tire.
- Check brakes to ensure nothing is rubbing. Any rub will produce false results.
- Take a few laps to warm up the tires.
- Record tire surface temperatures.
- Record road surface temperature.
- Record rider weight and bike weight.
- Measure power with hub based power meter. This is because hub based power meters measure power closest to the road compared to pedal or crank based power meters which absorb the mechanical losses of the drive train.
- Turn on AeroLab sensor and make sure power meter is connected.
Step 4 - Riding Protocol
The rider follows steps as well. A steady riding position is needed for this test.
- Rider must ride in the same, stationary state throughout the test. Body movements, like turning or dropping your head, produce inconsistent results. This takes some getting used to.
- Rider must complete out and back runs of 800m legs at three different powers: 180w, 220w, and 260w.
A Taste Of The Results
We wanted to give you an overview of the testing protocol for this article. We will explain all the results in an upcoming article that is focused on the data. Here is a little of what you can expect. Based on some initial testing, the following results are for on road rolling resistance for the Continental GP 5000 in 25mm vs 32mm.
The Meaning Of The Results
So what does this mean? First, a wider tire produces a lower rolling resistance on road. We are showing more than a 10% improvement before the impedance breakpoint, which is pretty significant. We do want to point out that these initial tests were for road tires, given our road familiarity. We will have more on gravel soon.
We also show the impedance breakpoint occurs somewhere between 95-110 psi. After the breakpoint, the Crr value increases quickly and we loose watts and speed. To produce the lowest Crr possible, our goal is to stay below the impedance breakpoint but get as close to it as possible. Future articles will cover this in greater detail.
Stay tuned next week for Part 11 of the FLO Gravel Wheel Design Journey where we discuss scanning tires and CFD.
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Our final results are normalized. Hope this helps.
Would be nice to see these results normalized with weight somehow.