Bike Tech: Aerodynamic Helmets

One of the simplest tests of aerodynamics lies in sticking your hand out of a moving car's window. Holding your hand slicing into the wind, there's hardly any resistance. But turn it flat against the wind and you'll encounter a strong force pushing you backwards. This force is the result of a multitude of air molecules colliding with the surface area of your hand. Minimize and refine the presentation of this surface area to the wind, and you'll experience less force. This principal is fundamental to the study of aerodynamics within cycling and directly relates to the aero helmet.

The prominent location of the head within cycling gives it great significance in regards to aerodynamics. Not only is it usually above the body in a vertical sense, it is also the first area to contact the still air ahead of you. This is where aerodynamic helmets come into play. Rather than the bulbous, muschroomesque shape and rough, vented surface of a road helmet hitting the wind first, an aero helmet allows a smooth, teardrop shape to slice through the wind. Not only does the smooth surface (with very few vents) facilitate the flow of air around the helmet, the shaping of the helmet in a teardrop shape keeps the air flowing along the helmets surface for longer, minimizing the drag-inducing disruption that occurs when air separates from flowing around the helmet into little vortices.


Compare the following two images. Notice how the integrity of the smoke is maintained when faced with a properly oriented aero helmet (2nd pic), as opposed to the disruption caused by the vertical orientation of the helmet in the top pic. (Note: Should you purchase an aero helmet, practice looking forward for extended periods to adapt to the strain on your neck. Not only is looking down extremely dangerous, you might as well wear the thing backwards).

Thanks to Getty images for the above photo

Computational Fluid Dynamics (CFD) utilizes a computer program to graphically illustrate fluid dynamics. Not a huge surprise there. But it is tremendously useful for determining the aerodynamic properties of different shapes. Check out the below CFD images of aero helmets produced by the Sports Engineering Research Group at the University of Sheffield for the British Cycling Team.

You can also view here a complete CFD model of an 'unhelmeted' cyclist (probably European) aboard a Felt model bicycle.

Not only does an aero helmet facilitate movement of air passed the front of the head, it also, when properly fitted, occupies the low pressure area that forms in the cradle of the neck (seen in the above as the rather vacant area immediately behind the head and above the neck/upper back). This is a significant and often overlooked benefit of the helmet that results from proper helmet selection (there are numerous models) matched to your triathlon-specific position on the bike.

Think of an aero helmet not as an aerodynamic replacement for a road helmet, but as a piece of equipment that will help integrate you with your bike into a single aerodynamic missile. It's commonly cited that at 25mph, 80% of a cyclist's energy is allocated towards overcoming air resistance. An aero helmet can most effectively combat this statistic when combined with a proper position.

I wish I could provide specifics in terms of how much time can be saved in a 40km TT, but that would be nearly impossible. I wouldn't be surprised if a good cyclist (say, 1:05 for a 40km) saved around 30sec - 1min.

At the very least, if you're training well and properly fit to a tri/tt bike, look into adding an aero helmet to your speed arsenal.