Wind Tunnel EZDisc Aerodynamics Testing

I recently took a trip to help out a good friend Clinton do aerodynamics testing of his wheel disc covers at the Silverstone Cycling Wind Tunnel.

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:

The wheel tests weren’t the only thing that went on. If you know me, you’ll probably realise that this constitutes a fun trip, however Clinton also offered to make it worth my while by allowing me some valuable time in the tunnel testing a few things on my bike setup.

While a lot of this was specific to my setup (e.g. bottle holder angle and placement), some of it is likely transferable to other people. The most obvious was for GB age group triathletes; to race internationally we have to buy and use the official kit. While I love that it’s GB kit, I’ve been grumpy about the apparent lack of aerodynamics for a long time so here was the opportunity to find out how bad it was.

I compared it to my Zone3 Aeroforce tri suit. Things I thought this might have in its favour:

1. It has short sleeves v.s. the vested GB suit. In the photo above I’ve got aerodynamic sleeves on as well, but I wasn’t using those for this test.
2. The Aeroforce material is designed to be aerodynamic with dimpling etc.
3. It fits well (there are limited sizes available of the GB suit – mine is the right size by height, but that leaves it very slightly too baggy). Although I’m currently heavier than my prime race weight, so this probably wasn’t an issue for this test.

Comparing testing using exactly the same setup except the suit, at 43kmph, my CdA increased from 0.2329 to 0.2353 (n.b. my lowest for the night was 0.216). For a middle distance race at 250 watts, that works out as 25 seconds slower. For the record, with that difference I might currently be the Aquabike European Champion in my age group (OK, that’s a massive stretch but I’m trying to illustrate the point! I did recently win my age group at Bedford Duathlon by 15 seconds).

I’m guessing GB Triathlon has a model where a single manufacturer pays a fee for the rights to produce the official GB triathlon kit. I wonder if it could switch to a model where any manufacturer could produce GB kit as long as it conforms to their colour scheme etc, and each paid them a small fee. That would drive competition and hopefully end up with more choice and better kit. Right?