An aero helmet is an aerodynamic helmet for cycling.
Why would you use one of these instead of a normal helmet?
Well, at speeds over 20 - 21 miles/hour air resistance starts to become significantly greater.
Therefore the power you need to produce to increase the speed you move at on your bike rises exponentially. In other words, you need to put more power down but for less reward.
This resistance is called drag, and aerodynamics is the art and science of minimising drag.
Using an aero helmet is a key way to reduce drag around your head, and therefore something that more and more triathletes in non-drafting races are using.
The more aerodynamic you are on the bike, the lower your drag and so the faster you will go for the same power output or effort. An aero helmet works by smoothing the airflow around your head and down your back, which reduces turbulence and enables you to slip thorough the air more effectively.
The only problem with these helmets is that to make them aerodynamic the vents need to be sealed off, so there is either no or limited cooling. Some helmets have a built in cooling system made of water or gels, but generally these are fairly ineffective.
When most manufacturers publish aero stats they make claims such as "10% improved aerodynamics". That is only for the individual part, i.e. the helmet. In terms of effect on performance, this has to assimilate into the combination of you and your bike.
So if the helmet accounts for ~10% of the drag of you and your bike, and your new helmet could save 10% of the drag of the old one, the net gain will be ~ 1% reduction in drag!
If you then choose one that does not suit your riding style and shape then the new helmet will actually make you less aerodynamic!
Combine that with a poor body position or other choices and your nice expensive helmet is only making up for deficiencies in other areas.
These pictures illustrate how an aerodynamic helmet can be used to good effect, but also less effectively.
In this picture below you see the athlete looking down with his helmet pointing straight up. This is generally not a good thing, as the airflow off it is creating turbulence all down his back.
Now take this picture and you can imagine how the helmet is allowing the airflow to run over the top/round the sides and smoothly down the back.
However all is not as it might seem from this image, this variety of helmet is a ‘long tail’ i.e. its quite a long helmet. If you are on a course which requires you to look around, or you are like the rider in the first image and look down frequently, this ‘tail’ will waggle around and create drag, not diffuse it.
So if you are going to use this type of helmet you need to be able to main this position for the majority of the ride.
Now the final image. In this picture below the rider has his head down, similar to the first image, but due to his helmet and how it fits his position it is not really compromising the aerodynamics around the helmet.
How much difference an aerodynamic helmet makes is very debatable and very difficult to quantify.
For instance, take two identically sized people in exactly the same position on exactly the same bike. One is really good and does the 40K in 52 minutes, the other is not so good and does it in 1h 5 minutes. The first rider will gain more from the helmet than the 2nd will, because he is travelling much faster and therefore the advantage of an aerodynamic helmet for them over a standard helmet is considerably more. This is not to say the slower rider shouldn’t use one, just that they can expect less return for the investment.
The one thing that we do know is that a good aero helmet, used in a good position at speeds over 22 – 23 m/hr is advantageous, in conditions where over-heating is not a limitation.
As with most products there is an extensive array of aero helmets, all with different features, shapes, sizes and effectiveness. There are long tail and short tail helmets, there are some with pimples, some with additional fins, or visors. How effective these features are for you is very difficult to quantify.
Key point: The thing to remember about any aero piece of kit is: do not look at the item in isolation, look at it as a whole; how does it work with you and your bike?
The right helmet for you is one that: