Wind Tunnel Test: How Do Aerodynamic Wheels Differ?
Last month, the Bike News team conducted tests in the wind tunnel at the renowned Silverstone Sports Engineering Center, where they put WorldTour superbikes to the test. They compared these top-tier bikes with others in a direct showdown. Alongside the 11 superbikes, the team also brought their "base bike" — a 2015 Trek Emonda ALR equipped with standard square-section wheels, rim brakes, external cables, and round handlebars, without any aerodynamic optimization.
As expected, the base bike was slower than the superbikes. In their raw data, after averaging two rider-motorbike tests (one at the start of the day and again at the end), the team found that the base bike was 23.06 watts slower at 40 km/h than the average result of the superbikes. This means that to ride at 40 km/h, a rider would need to expend 23 more watts on the base bike compared to riding a typical superbike.
However, all the superbikes were equipped with aerodynamic deep-section wheels. So, what would happen if they swapped the base bike’s regular wheels for a similar deep-section option? The team decided to find out for themselves.
How much of an impact do deep-section wheels really have on cycling performance? Let’s find out!
They wanted to understand if upgrading to deep-section wheels could completely close the previous 25-watt gap. Would the performance improve significantly? And, how does the cost-effectiveness of deep-section wheels compare to something like a new helmet?
If you have an older entry-level bike like their Trek Emonda, is upgrading to aerodynamic wheels a smart investment? Do they really make a noticeable difference, or are they just for looks? They decided to find out through this test.
For the wheels, they chose a high-value option from the now-defunct British brand Prime, specifically the RR-50 V3 model.
These wheels have a depth of 50mm and an internal width of 19mm. They also mounted the same 25mm Continental GP5000 S TR tires that were used on all the other test bikes to ensure consistency. Before the brand closed, these wheels retailed for about £800 (or $900).
Visually Transformative, But Does It Actually Make You Faster?
The Results
They tested each bike under seven different yaw angles, which refer to the angle at which the wind hits the bike and the rider. A yaw angle of 0 degrees means the wind is hitting the rider head-on, a perfect headwind, so to speak. A higher yaw angle means the wind is coming from the side.
In this case, they tested from -15 degrees (wind coming from the left side) to +15 degrees (wind coming from the right side), in 5-degree increments, for a total of seven different angles.
The data provided by the wind tunnel is CdA, which stands for Drag Coefficient x Surface Area. The drag coefficient reflects how the shape of an object affects how easily air flows around it, while the surface area simply refers to its size. In simple terms, the lower the drag coefficient, or the smaller the object, the easier it moves through the air, and thus, the faster it will go for the same amount of effort.
This chart shows the CdA results for each bike at seven different yaw angles, ranging from -15 degrees to +15 degrees, in 5-degree increments. The higher the CdA, the slower the bike.
What's really interesting is that the deeper wheels were actually slower at lower yaw angles. This is likely because these wheels are significantly wider than our base wheels, which increases the bike's frontal surface area.
However, when the wind comes from wider yaw angles, the deep wheels really come into their own, providing more of a "sail" effect, capturing the wind and helping propel the rider forward.
This chart shows the average CdA values calculated from the data captured at seven different yaw angles. On the left is the average CdA for our 11 superbikes, in the middle is our reference bike, and on the right is the reference bike with aerodynamic wheels installed.
By averaging the raw CdA data, they found that with the deeper wheels installed, the CdA on the rider's bike was 0.3640. This is 0.0062 lower (and therefore faster) than the reference value.
The team calculated the power required to maintain a speed of 40 km/h with each of their bike configurations. On the left is the average power for the 11 superbikes, in the center is the base bike, and on the right is the base bike with aerodynamic wheels mounted.
By calculating the CdA values, the team began to understand the real-world differences between configurations.
The data shows that the superbikes require an average of 282.41 watts to maintain 40 km/h. The base bike, as previously mentioned, consumes 23.06 watts. Even with the aerodynamic wheels installed, the power difference didn't decrease much. Ignoring the margin of error, the aerodynamic wheels saved only 5.89 watts.
In real-world terms, this equates to a 25-second time saving over 40 kilometers if you ride at 250 watts, or a speed increase of about 0.24 km/h for the same effort. If you increase your power to 350 watts, the speed increase rises to 0.27 km/h.
However, it's important to note that when considering the margin of error, the difference between deep-section wheels and regular wheels may not be as significant. The margin of error in the team's test was calculated at 3.91 watts, meaning in some cases, regular wheels could actually be faster than deep-section wheels.
As shown in the two bar charts above, the error bars for both relevant data sets overlap, meaning that in the best-case scenario, the base bike could be faster than the deep-section bike. On the flip side, in the worst-case scenario, deep-section wheels could be up to 13.7 watts faster than the base bike at 40 km/h.
Conclusion
From a statistical perspective, given the margin of error, the team cannot definitively conclude that deep-section wheels are faster than shallow wheels.
However, by reviewing the raw data and using practical judgment, the team reasonably believes that deep-section wheels do offer some performance advantages.
In terms of cost per watt, given the high price of deep-section wheels, the performance gain is minimal. Based on the raw data, the power saved with deep-section wheels is less than six watts, which, at a retail price of £800 ($900), equates to about £133.33 ($150) per watt saved.
In 2022, the team took a selection of wheels to the wind tunnel for testing. The results showed that the difference between the best and worst aerodynamic wheels was only 3.87 watts, with no direct link between price and performance. This suggests that upgrading to a premium aerodynamic wheelset yields limited additional savings over budget options.
Interestingly, the main difference between deep and shallow wheels becomes noticeable only at larger yaw angles, which are relatively uncommon, meaning the real-world performance gain may be even smaller.
Of course, aerodynamics isn’t the only reason to buy modern wheels. Many modern wheels are lighter, wider, and offer better handling. However, if the only reason you’re considering deep wheels is for an aerodynamic boost, you may want to think twice before investing all that money... even if they do look cool.
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