Here’s how the five wheelsets were tested against each other.
- We tested each wheelset on a size M54 Scott Plasma 20 triathlon bike
without a rider.
- Every wheelset was tested with Continental GP4000 S clincher tires.
- No accessories were mounted on the bike.
- Every wheelset was tested at 0, 5, 10, 15, 20 and 30 degrees of yaw.
- Two data sets were taken at each yaw angle.
- The test was run at 30 mph of wind speed.
Tunnel test shortcomings
Even wind tunnel testing isn’t perfect. These limitations could possibly create a difference in the drag measured in the tunnel and the resistance when racing these wheels on the road.
- Air passing over the rider affects the drag created by the rear of the bike, including the back wheel. This test didn’t include that variable.
- Data were taken only on one side of the bike, but air passing over the drivetrain from different angles impacts the drag.
- All wheelsets were tested with 23c Continental GP4000 S clincher tires. This is a commonly used race tire, but other tires could potentially reduce drag for specific wheelsets. For example, Bontrager designed the R4 Aero tire specifically to complement the Bontrager wheel.
Yaw Angle Explained
A moving rider experiences wind differently than a stationary object. Rider speed and direction change the wind speed and angle he experiences. Faster riders experience lower yaw angles than slower riders. Below is a yaw and wind speed calculation for a cyclist riding 20 mph into a 10 mph wind angled 45 degrees from his direction of motion.