Nov 24, 2007

Motorcycle Helmets: Why do all the big names harp on and on about vents and airflow?

At the end of the day, no matter how much technology goes into your helmet. You are still placing your head in an enclosed, tightly-fitted spherical box. So the least the helmet makers can do is make you comfortable, right? Vents are the accepted way to control airflow through the helmet. Initially, there were only intake vents, but with wind tunnel testing (really) the latest and greatest lids emphasize exit vents as much as intake vents. The massive diffusers you see nowadays on some of the lids exist for that purpose, and to smooth the aero profile of the helmet. Most top-line lids today, in fact, offer as much control to the rider over air intake as over air exit.

Most often, the helmet will have one chin vent at the bottom center of the visor, and one or two vents above, ranging from just above the visor center to the crown of the helmet itself. On the back, similarly, there can be sets of exit vents on top, at the bottom and sometimes, there is even one on the bottom of the helmet, a little inset from the bottom rubber ring on the lining. Does it work? Leaving an airconditioned room having worn the lid inside for five minutes or so, you can actually feel cold air on your shoulders when you start riding.

Airflow refers to the aerodynamic profile of the helmet. The first time you cross 150 kph on a motorcycle (don't scoff, you'll be doing that sooner than you think), you will how good or otherwise your helmet is. The AGV Pacific, for instance, my personal pick for the best Indian lid, squashes flat against your nose at anything over 130 kph. Designers can design the helmet to smooth airflow. There's a reason for this. As the air leaves the helmet, the smooth flow breaks up behind the helmet, and that's the deep bass fluttering you hear inside. Diffusers can help cure this.

Similarly, helmets with plastic plates over the visor mounting (Arai, Suomy, Vega etc) tend to be noisier because the air catches on the edges and adds whistling sounds. Further, top of the helmet vents also tends to add noise. The plates also make the process of changing visors – I ride with a dark on in the day and a clear one at night – fiddly and cumbersome.

Wear a helmet and stand in a closed, silent room. You will hear nothing – the helmet makes no sound of its own. All the noise you hear is just wind. Given that wind noise can reach almost a 100 dB, well past the safe hearing limit, I think it's important to pick quiet helmets.

Related links in this series:

Other links on helmets

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