After much testing and analysis, here is the first release of data following our recent trip to the GST Gesellschaft für Strömungsmeßtechnik mbH (as used by Canyon), in Southern Germany.
Read on to find out how the Hunt 50 Carbon Aero Disc wheels with a 25c Schwalbe Pro One tyre produced the lowest drag on test!
PLEASE NOTE: This release does not include any prototype results. The development of a super-wide, disc-specific aerodynamic wheelset is the primary purpose of this project, however, this article pertains specifically to the benchmarking of our existing aerodynamic carbon disc-specific wheelset, the HUNT 50Carbon Aero Disc.
For our testing, we used the class-leading Canyon Aeroad Disc, combined with a rear ENVE 4.5 AR SES wheel across all runs. From an aerodynamic standpoint at normal yaw angles, the front wheel is the primary contributor to drag (after the rider), with the rear wheel contributing only a small amount to total drag. Hence, the primary concern was consistency across the runs, and the use of the same rear wheel to isolate the front wheel performance as the control variable.
The runs were conducted with a wind speed of 45kph (28mph), and the wheels spun up to an equivalent riding rotation (around 356rpm for a 700x25c wheel). The bike was mounted on a rotating bed, allowing the entire bike to be rotated relative to the wind tunnel flow, simulating a range of yaw angles.
What's all this about yaw angles?
The yaw angle is the effective direction of airflow hitting the bike/rider, resulting from a combination of riding speed and ambient wind speed/direction. As a simple example, imagine you are riding at 30kph in a straight line with no wind; the air is hitting you directly head-on at 30kph. Now imagine that at the same time, there is a wind blowing from exactly 90 degrees to your left, also at 30kph. The combined effect of your 30kph forward speed, and the 30kph wind from the left, is an effective airflow coming from 45 degrees to your left at a speed of around 42kph (remember your trigonometry lessons from school?).
The yaw angle, in this case, is 45 degrees (pretty high!) Realistically, you are not usually cycling through 30kph winds, and so the yaw angle is lower than this. To provide a good representation of the yaw angles likely to be experienced at 45kph, we tested over a yaw angle range of ±20 degrees.
For the first round of testing, we fitted all the wheels with the Schwalbe Pro One 25c tyre, a tyre width which pairs nicely with the rim width of our 50CAD and most of the market-leading aero wheels. The plot above shows drag force against yaw angle. Looking at the centre of the plot (low yaw angles), we can see that under these conditions, the 50CAD positions itself very well among the wheels tested, coming out with the lowest drag values across most of this range. As the yaw angle increases to 12 degrees and above, we see that the drag values for the 50CAD stays close to most of the other wheels. The Zipp 303 NSW performed particularly well at the higher yaw angles, but at lower yaw angles it is the highest drag wheel we tested. Additionally, unlike most of the other wheel on test the 303 NSWs are not tubeless ready, so out on the road you'd lose the lower rolling resistance, increased comfort and puncture protection offered by tubeless tyres!
So what does this mean for the Hunt 50CAD? Well, we think these results back up our own claims that the 50CAD is one of the lowest drag aero wheels for its depth on the market when paired with the Schwalbe Pro One 25c tubeless tyres, and this applies across the range of yaw angles tested here. This is great news for Hunt customers!
So where do we go from here?
Many of our customers are looking to wider 28c tyres for their improved comfort and rolling resistance, so we wanted to compare aerodynamic performance when running a wider Schwalbe Pro One 28c. This tyre comes up a few millimeters wider than most aero rims, so drag performance here was expected to drop across all the wheels, as the rim-tyre interface is less well matched.
We can see in the plot above that the drag increased for all wheels, and the performance of the Hunt 50CAD fell; an expected result given the rim is optimised for the 25c tyre. We tested a few additional wheels with the 28c tyre combination, looking to compare performance across a wider portion of the market for this increasingly popular tyre choice. Notably, we included the ENVE 4.5 AR Disc, which is designed requires a minimum 28mm tyre width and uses a hookless rim design meaning it is only compatible with tubeless tyres. With its 31mm external rim width, the ENVE is clearly optimised for 28mm tyres, and this shows with it experiencing the lowest drag values of all the wheels tested at all yaw angles.
So what can we take from this second round of testing? Firstly, we know that our 50CAD is not optimised for a 28c tyre, and although the wheel still performed well, it clearly performs best with a 25c. But what really stood out was that none of the wheels tested with both 25c and 28c tyres appeared to be optimised for peak aerodynamic performance when considered as a global system with a 28c tyre. And the wheelset that was optimised for a 28c tyre, the ENVE 4.5 AR Disc, is not even compatible with 25c tyres, and cannot be run with a standard clincher - still a popular choice for many people who prefer the flexibility of a standard clincher (swapping your tyres often for example).
Why should you be interested in these high yaw angle results?
A widely used method of measuring the overall aerodynamic benefit of a wheelset is Wind Averaged Drag based on the Mavic Ponderation Law, which considers the average amount of time spent at different yaw angles when riding, based on measurements taken by Mavic during testing. In the chart below, we can see that less than 10% of a ride would be spent with a block headwind or no wind at all. Even more surprisingly, over 25% of the ride would be spent with wind yaw angle of 10 degrees or more! What this shows is that yaw angle aero performance will have a significant impact on the total drag power a rider has to overcome and that zero-angle optimised wheelsets will not offer maximum aero benefit to most riders.
With this in mind, our Engineering and Product Manager, Luisa Grappone, has calculated the wind average drag for the wheels tested here to compare the performance of the wheels based on this Mavic Ponderation Law. In the charts below, we can see the Wind Average Drag data as well as the actual tyre widths when fitted to the wheels. The significance of this is that the wheels all bring up the tyres to different widths, and therefore although all are running the same 225/28c tyre, in reality some of these wheels result in a tyre notably wider than this. This will have an effect on rolling resistance, grip and comfort, as we know that a wider tyre has benefits in these areas.
We can see here that the performance of the 50CAD with a 25c Schwalbe Pro One tyre is excellent, showing the lowest Wind Averaged Drag of any of the wheels in this test! This is incredible news for Hunt customers! In addition, the 50CAD brings up the 25c Pro One tyre to one of the largest widths of the wheels tested, meaning not only are you getting the lowest drag, but also some of the highest grip, lowest rolling resistance, and best comfort.
Moving up to the 28c tyre, we can see that the performance of the 50CAD drops off relative to the other wheels tested as a result of the rim not being optimised for the wider tyre. However, taken in context of the price point and the wheels' versatility (tubeless and clincher ready and able to take a wide range of tyre widths), the 50CAD wheels offer very impressive performance.
Going forward (faster)
So, with riders increasingly looking to 28c tyres, can you achieve low aerodynamic drag whilst enjoying the comfort, grip and low rolling resistance these tyres offer? In partnership with the expertise of engineers from Schwalbe, and the experience of our in-house aero-genius Luisa Grappone, we are in the process of designing a wheelset that does just that: maximum aerodynamic performance specifically optimised for 28c tyres. The ultimate modern aero road wheelset.