The Science


Wind Tunnel EZDisc Aerodynamics Testing

The idea was to validate that putting one of these covers on your wheel actually makes you faster. Spoiler – it does!

We had an array of quality carbon wheels of different depths with EZDisc covers for each, one aluminium box rimmed training wheel, one relatively cheap disc wheel and one relatively expensive disc wheel to play with.

The test itself was with the wheels on my TT bike, with the wheels spinning, without a rider. Why? The rider adds far more drag than a wheel so unintentional movements can mask the differences the wheels make.

We tested with wind speeds of 30, 40 and 50kmph, with wind angles of -15 degrees through to 15 degrees.

The results were unequivocal!

This graph shows lines, one per wheel, for the aerodynamic drag (the “CdA“), including the bike, against the wind angle (the “yaw”). It’s averaged across the wind speeds.

The lower the CdA, the better.

As you’d expect the training wheel performed worst (the top line in dark grey).

Then there is a group of all the carbon wheels. Surprisingly the depths from 38 to 88 all performed similarly, with the deeper rims just outperforming the shallower ones at higher yaws.

Then there is a grouping containing the real disc wheels and the disc wheels with covers. There’s very little difference between these.

These distinct groupings show the disc covers improving the aerodynamics of the wheels up to the same performance as normal disc wheels! Bearing in mind these are a fraction of the cost, this is a pretty big finding!

What do those figures mean in terms of racing? Plugging the differences between the wheels with and without the disc into a calculator or directly using the formula you can work it out:

That’s a pretty impressive improvement, especially considering these were some pretty high end wheels to start off with. Comparing the aluminium box rim training wheel to the 88mm with an EZDisc cover or real disc wheels, you can see it’s practically the same time savings:

We also in the earlier days used Aero Weenie to crunch the numbers from our tests, this is in real world conditions. - All Aero, All the Time

For our formal testing we manage all the variables as best we can. We conducted our repeat runs on the same route, on the same day with one rider on one bike, just changing the rear wheel from a standard one to one with an EZDisc fitted.

Route data
Weather Data