Ah, the wheel. It’s been around for thousands of years, yet we’re always trying to find a way to perfect it. While a wheel has always been the same in principle–round, it has continuously been modified to fit certain purposes. Bikes are a perfect example of this, especially when it comes to cheating the wind.
Most folks would probably agree that a thick mountain bike wheel with lots of spokes and wide tires isn’t as aerodynamic as a narrow road wheel with fewer spokes and skinny tires. That is basic, common sense if you know anything about aerodynamics. However, subtle differences in wheel aerodynamics are just that…subtle. A seasoned triathlete or cyclist knows that a disc wheel in the back makes you faster. Have you ever seen Lance Armstrong time trial without a disc wheel in back? However, what’s the best front wheel. There are lots to chose from and it’s difficult to understand why one person uses one over another. OK, so maybe you don’t have a ton of money and can afford one front wheel, but let’s say you have your choice of any on the market. What do you do?
I’ll use Hed wheels as an example. Steve Hed is a aerodynamics guru who got into the cycling game back in the days when Duran Duran was still topping the charts. His company has always been at the forefront (and often battling with the likes of Zipp) of creating the most cutting edge aerodynamic wheels. My cycling team–XXX Racing/Athletico–is fortunate to have Hed Cycling as a sponsor so we’re able to race on some of the best wheels around (just like the HTC-Columbia professional cycling team).
One of the most staple Hed wheels has been the trispoke, also know as the H3 or H3C. The shape is unmistakable and looks very different than traditional spoked wheels. Over time, Hed has also experimented with wheels with different rim depths and thicknesses. As I mentioned above, a disc wheel is the most aerodynamic, but can make controlling a bike very difficult when used as a front wheel (it can actually help make the bike more stable when used in the rear). Thus, the goal is to find the most aerodynamic wheel in the front, while allowing the rider to adequately control the bike.
Hed has created an Apparent Wind Calculator to help you decide which wheel to use. You input wind speed/direction and rider speed/direction and it determines the actual wind force that the rider will be facing, as well as the yaw angle. The Apparent Wind Calculator can be found here. You can then use this data combined with the aerodynamic chart for each of their wheels here. I’ll show you a couple of examples below.
Above iss an aerodynamic chart comparing a Hed Stinger Disc, Stinger 9, H3C, and a Zipp 404. The lower the number the better, because that means less drag. Theoretically, a negative number would “push” a rider along.
Our first scenario above has a rider heading North at 25 MPH. He is experiencing a 7 MPH wind out of the WNW. At this speed and direction, he is experiencing 27.8 MPH of wind resistance with at a yaw angle of -14.2 degrees. So, should he use a Stinger 9 or a H3C Using the chart above, it seems as if the Stinger 9 would be the best choice. Although the H3C isn’t bad, he would actually be experiencing negative drag in this situation with the Stinger 9. Thus, I’d vote for the Stinger 9 in this situation.
Now, let’s look at more windy conditions. In the second scenario above, the rider is still traveling North at 25 MPH with a WNW wind, however, now the wind is 15 MPH. This means that the wind resistance has picked up slightly at 32.4 MPH, but the yaw angle has increased dramatically to -26.6 MPH. Using the Hed aerodynamics chart, the H3C looks better as the performance of the Stinger 9 gets worse at larger yaw angles. Thus, I’d vote for the H3C in this situation.
I’m lucky enough to own both of these wheels. I usually go with the Stinger 9 when wind conditions are <10 MPH and the H3C when the wind is >10 MPH. When choosing wheels, it’s also important to consider road conditions, tire width, pressure, etc. However, you can see how choosing a wheel based on aerodynamics is a smart–if not “Hed to Hed”–decision.