Subsonic Flow

There’s been a lot of chat about Gorilla Greipel’s new chrome dome helmet, but lets look at the facts and come to the understanding that these are here to stay, especially in the northern classics & more generally in colder climates like ours.

A bit of History

Proper polystyrene protective helmets began appearing the very late 80’s in Scottish racing, they became part of the rules in about 1991 & the old foam & leather ‘bunch of bananas’ or ‘hairnet helmet’ became confined to history forever. The very early helmets were a little bulky, but then Giro, Specialized and a few others developed some good looking (at the time) lids and things moved on from there. Greg Lemond was an early pioneer and trailblazer of everything aero, likely prompted by sponsor pressure too, he promoted Giro helmets and used a very early closed vent version of the ‘Air Attack’ model called the ‘Giro Track Attack’ which reputedly had a 5% aero advantage over a bare head, although nobody was listening back then (things have gone full circle now and a new ‘Air Attack’ now exists along with a development ‘Track Attack’). Meanwhile the pro’s were regularly sitting at the side of the road protesting about having to wear the things, while us amateurs were just getting on with it. Things changed, the pro ranks were allowed to discard the lids on the last mountain of a stage race, then eventually they had to wear them all the time, that’s where we are right now.

Some Technicalities

You can understand to some extent what the pro’s were annoyed about, early helmet technology had resulted in some not particularly well vented examples, they had to wear what their sponsor gave them, so helmet choice/luck became part of the game. Helmets then became increasingly vented to keep the top riders happy, those riders needed them to have enough airflow over their head for 50 minute climbs in 30 degrees heat a low speeds. All the adverts were stating the amount of vents, as if it was the key selling point to ‘normal’ cyclists.

Now consider your average Scottish race, you’re unlikely to be climbing many hills over 5 minutes, at most it’ll be 10 minutes climbing, temperatures on the warmest day are 25 degrees one day a year, but likely you’re racing in an average of 15 degrees, punching over small hills at a reasonable speed. Do you really need as much airflow as the 50 minute, low-speed, 30 degree heat boys? Of course not, don’t kid yourself on.

This brings us to ventless aero helmets for road racing. They currently look ridiculous to us, but so did all helmets when we first saw them, maybe we’re just not used to them yet. The Sky team have been using them for a couple of seasons with their Kask helmets. Although these ones show the vents and retain the look of a vented helmet to some degree, although the yellow ones were ridiculous. So we have a half way house here, some manufacturers are trying to retain a vented look, while others like Lazer are going full aero, which is the likely outcome over the next couple of years. The vague vents will slowly disappear in order to become more aero, the UCI will change the rules and stop everything becoming too aero and un-Merckx like. So we have a hidden race, between an acceptable look and the desired function, to go faster. Greipel’s claimed sprint max speed was 74km/h in one of the Tour down Under stages, so how much advantage did this aero hat give himself and his team, with Henderson dropping him off into the final sprint at his claimed 70km/h? There’s obviously no data out yet, but Cavendish’s worlds helmet cover on his Specialized lid will explain that it’s a measured ‘marginal gain’ and worth enough watts to encourage manufacturers to develop products. You’ll hear terms like ‘subsonic flow’ ‘boundary layers’ & ‘turbulence’ being banded about in marketing material, it’ll all become very technical, they’ll all claim to be the fastest.

Helmets for Scotland (or anywhere cold)

Do we need all these vents, as explained above, we don’t. So as you’ll see in the northern classics from now on, non vented helmets will become prolific, even more so in cold markets like our country. If pro’s can wear non vented helmets in stages of le Tour, if we’re honest with ourselves, we could wear them all year round. Especially in winter, they would probably make a significant difference with reduced airflow and nice warm head. We’re currently wearing helmets with 20 something vents in minus temperatures, there’s no logic to that. It comes down to aesthetics, vented helmets look correct right now, only because since 1991 we’ve got used to them, previous to that anything other than a hairnet, a bare head or a cap looked right. Times change and in 5 to 10 years time, once there’s plenty of pro photos out there of top riders saluting the crowd in an aero road race helmet, you’ll think aero road helmets are the thing to wear in the bunch or training ride.

The future of headwear

Expect Assos & Rapha to ‘develop’ breathable under-aero-caps to complement your new fast lid, where there’s a marketing opportunity, there’s the momentum to make anything stick. Aero, ventless road race helmets, you’d better get used to them, they’re not going away, in fact, they’re probably a good idea in Scotland, you’ll get used to how they look.


  1. Logic is a good approach. I took the lo-fi approach and made this lo-fi aero helmet for a club hilly TT. I took compliments and pelters in equal measure but you could feel the difference. It looked worse than a Kask and took a long time to get the sticky residue off. And I think technically against the rules, too.

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