Helmet Selection Variables and Aerodynamics
A version of this article was originally
published in Triathlete Magazine
I’m interested in getting an aero helmet. How should a properly adjusted helmet fit and which helmet is the fastest?
Multiple wind tunnel studies indicate that aero helmets offer one of the highest ratios of aero benefit to dollar cost of any single piece of equipment currently available to a time trialist or triathlete. With estimated median aerodynamic drag benefits for most amateur riders ranging from 3-6% (8-13 watts), the potential benefits of an aero helmet are hard to ignore.
The only independent wind tunnel test of aero helmets that I am aware of (Blair, 2007) was performed under brand anonymity. However, the test concluded that while some models tested better in certain conditions than others, all of the aero helmets tested offered aerodynamic benefits at yaw angles of 0 to 15 degrees (the test did not go beyond 15 degrees) when compared to a standard road helmet. The summary also stated that, “the results show that there is no clear choice among aerodynamic helmets for all riding conditions…”. Like any piece of aero equipment, field or wind tunnel testing on the individual rider who will be using the helmet is the only way to discern subtle aerodynamic differences between models.
When it comes to aerodynamics in general, and aero helmets in particular, things are rarely as simple as wind tunnel numbers may make it appear. Aerodynamics is a “package deal” and your riding technique and form are of great importance. The best TT riders and triathlon cyclists tend to have exceptional riding technique and part of optimizing this technique is knowing that their riding position and equipment are working to the fullest potential. In the case of aero helmets, this means holding and maintaining the helmet in as stable and aero a position as possible. The more stable and consistent the head and upper body position, the more significant the likely aerodynamic benefit as the wind will maintain a more laminar (smooth) flow around the helmet and the rest of the rider and equipment. If you know that you often stretch your neck, turn your head to the side, or tuck your chin when riding, an aero helmet’s aerodynamic benefits could be significantly diminished.
Outside of aerodynamics, as with any helmet, comfort, weight and ventilation are significant variables too. The importance of comfort in a helmet is self-explanatory and an ill-fitting helmet will not protect you the way it was designed in the event of a crash. A properly sized helmet will fit comfortably snug, resting about 1” above your eyebrows and contacting the top of your head as well as the front and sides. Your helmet straps should be close to your head and relatively taut with the chin strap adjusted so that when you open your mouth, the strap pushes against the bottom of your chin, but does not limit your jaw. A well fit helmet will stay firmly in place when you shake your head and there should not be gapping between the helmet and your head. A good way to check shell size is to place the helmet on your head and pull it straight back and forth and side-to-side. A well fit helmet will not have space between the shell and your head and will not knock your head when you perform the maneuver above.
Helmet weight is important in much the same way that the weight of a running shoe is notable. While few of today’s helmets feel heavy on their own, you do need to support the weight of your head and helmet with your neck and, over a long ride, ounces can add up. Aero helmets are usually heavier than standard road helmets and while the lightest helmet is not always the best helmet, make sure that your helmet is light enough so that it does not become burdensome. Especially if you are a distance athlete, remember that you are likely going to be logging some significant miles and time on your bike. An aero helmet that is reasonable for a one hour ride might not be as functional for a six hour ride.
Ventilation is also a significant item to consider when buying a helmet. One of the more effective ways to lower drag is to minimize the number and size of wind disrupting vents. Make sure that your helmet is adequately ventilated for your use, as even the most powerful and aerodynamic engine will seize up if it overheats. Other design elements, like ear covers and eye shields, can further enhance the aerodynamics, but they can also reduce ventilation. For this reason, some popular aero helmet brands, like Louis Garneau, offer multiple models to match the needs of a variety of athletes. The LG Rocket and Super Leggera models offer full ear coverage and can be fit with an optional eye shield, making them great for time trialists and triathletes who are willing to trade a little ventilation for aerodynamics, while the Chrono model is cut higher for those athletes who want greater side ventilation in an aero shape. For the rider who wants ear covers or a shield on some rides and may not on others, the Rudy Project Syton proves that a modular design offers the benefit of flexibility, allowing the rider to add or subtract aero features as wanted. While ventilation and aerodynamics are sometimes (but not always) conflicting design aspects, you have to determine what is a reasonable balance for your body and riding. If you are doing 40Km time trials, the aero benefits of integrated ear coverage and eye shields are likely worth the extra heat, if you are doing an Ironman in the heat of Hawaii, they may not be.
With so many strong options from the aforementioned brands, as well as Giro, Spiuk, Lazer and others, there is an aero helmet that will fit and work well for just about any rider and event. Find an aero helmet that fits you well and practice your aero riding technique and you will find yourself riding faster without working any harder.
Ride hard and smart!