Interesting test of wheel aerodynamics, alloy rim matches Zip 303

[biker jk]

I stumbled on this test of the aerodynamic properties of some alloy rims versus a Zipp 303. The results are quite interesting in that the Zipp 303 only started to outperform the best alloy rim from yaw angles of 7.5 degrees and above. However, just over 70% of riding is at yaw angles of 5 degrees or less. Calculating the yaw frequency weighted drag numbers showed that the Zipp 303 was matched by the Al 33. Moreover, the Kinlin X31T was more aero than the Zipp 303 and other allow rims tested at yaw angles of 5 degrees or less. Unlike the Al33, the Kinlin 31T isn't a toroidal shape and so starts to lose its aero advantage at higher yaw angles. The Zipp 303 clincher rims weighs around 500 grams, the same as the Al33 and Kinlin X31T. As such, I can't see why you would spend thousands buying a Zipp 303 wheelset versus say a wheelset built with the Al33 rim.



https://s5.postimg.org/ykac7jabr/Aero_wheel_test.jpg

[Alex Simmons/RST]

At low yaw what matters for aero on the front is being narrow, a low spoke count, bladed spokes with some rim depth. It's partly why the old Campag Shamal was such a great wheel, especially on the track. The rear presents some different issues as the aft air turbulence matters.