EZ Disc® Cover (650-B-C) 10-15 Watt Saving®

One of the first areas riders look to upgrade for aero improvements are their wheels. In time-trial and triathlon racing, many people equip their bikes with a completely covered rear wheel or a full rear disc wheel.

This blocks all air from getting caught in the rear wheel and keeps it moving past quickly. On windy days, the disc may also create a sail effect, pushing the rider even faster.

But bolting one of these on is not cheap. Just that rear wheel alone can cost anywhere from (£1,000 to £4,000).

To make this rear wheel advantage more accessible to the masses, the team at EZGains has created an elegant solution to this problem.

They’ve developed a simple cover made of durable and lightweight material that slips over your existing wheel, connecting securely and creating the SAME aero gains as if you purchased a fancy rear wheel.

In fact, some testing suggests that depending on the wheel you install it on, the cover may perform better than a full disc wheel due to the fact of what quality hub you have, cheap disc wheel or old one often means cheap or poor-quality hub, this means if you already have a good quality wheel and add the EZ Disc this can enhance your gains, as the aero gains between and Disc and EZ Disc identical.

Testing this out ourselves, we found that installation was quite simple and could be done at home with the appropriate tools (most will need a lock ring tool).

Once on the bike, the feel and performance was evident. It really showed its stuff on those fast descents, capturing an extra mile or two per hour in comparison to our 80mm deep section rear wheel.

The EZDisc was tested at Silverstone Sports Engineering Hub and compared to a top end disc wheel “graph below at 40kph, the orange line is a EZDisc with a lower CDA".

Tests 31st January 2023 using rim tape and a rider holding the exact position within the green lines set out from base ride.

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 the saving.

The above tests were conducted not using the rim tape in 2021 and without a rider.

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 EZ Disc / 88mm / 20mm "its clear difference with an EZ Disc. We also in the earlier days used Aero Weenie to crunch the numbers from our tests, this is in real world 

For our formal testing we manage all the variables as best we can. We conducted our repeat runs on the same hilly 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.

When testing out door you will always get a more positive result then the wind tunnel testing as you will also have a "push factor" from side and rear winds, any front winds will travel over a smoother surface faster.

We have now also had feedback for 100s of riders with over 5,000 EZ Disc riders confirming the below average time savings.