Head first: Do aero helmets make a difference?
The helmet market has been turned on its head over the past few years. Aerodynamics has been the marketing spark, and nary a helmet has been announced without a nod toward drag reduction.
A rider’s head is like the nosecone on a fighter jet, the first piece of equipment to hit oncoming air. Airflow over the head and onto the rest of the body has a vast impact on overall aerodynamics. Beyond evaluating the differences between top aero helmets, this test sought to determine precisely how much there is to be gained with what is, in the grand scheme of cycling equipment, a relatively cheap purchase.
As we stepped into the A2 wind tunnel in North Carolina, the question was simple: How much aerodynamic efficiency can be gained from swapping lids?
Five helmets were tested. Velo‘s 2014 Editors’ Pick road helmet, the Giro Aeon, was used to provide a baseline comparison. Giro makes no aero claims with the Aeon, touting only its low weight and exceptional cooling. It was not designed to improve aerodynamic efficiency.
Three popular aero road helmets were tested, one each from Giro, Specialized, and Kask. Each is something of a hybrid between a road and time trial helmet, designed to be cool and comfortable and also reduce drag. To complete the spectrum, a Kask Bambino time trial helmet was tested.
Each helmet was tested from 0- to 20-degrees yaw, or wind angle, on an actual human. Testing with a person is difficult, as small changes in body position can have a dramatic impact on the results. The solution is to conduct multiple test runs, removing outliers. The engineers at A2 are confident that the data presented here is an accurate representation of the aerodynamic efficiency of each helmet.
Results were calculated using the wind average drag (WAD) algorithm that is frequently used by helmet manufacturers, and was originally developed by engineers seeking an improved understanding of automobile aerodynamics. It is a weighted average of multiple wind angles based on the probability of that wind angle occurring in the real world.
The Kask Bambino time trial helmet was the most aerodynamic. Its smooth shape and lack of venting cut through the wind better than any other in this test.
Among the aero road helmets, the Kask Infinity was fastest, but only with its front vent closed. This helmet, used by the Sky squad at the Tour de France, has a large front vent that can be opened and closed, depending on conditions. With the vent open, the Infinity was only marginally better than our Giro Aeon baseline.
The Specialized Evade was the next fastest, followed closely by the Giro Air Attack. Both claim to provide ample cooling, and top pro teams have used both helmets even on hot days.
As a point of reference, if you switched out the stock aluminum Mavic Cosmic wheels to pricey carbon Zipp 404 Firecrest wheels on a Cervélo S3 aero road bike, WAD is lowered by 65.9 grams. To get those efficiency savings in a helmet swap, a rider would have to switch from the Aeon road helmet to the unvented Kask Bambino time trial helmet. That’s not practical for someone riding on the road; it would be too hot on most days.
In all, the aero road helmets we tested will decrease drag by about one-third to one-half as much as changing to an aerodynamic wheelset. But the price cannot be argued with.