Best aero road helmets: tunnel- and road-tested

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This article was originally published on BikeRadar.

Once a curious little niche just three years ago, the aero road helmet category has since exploded with nearly every company including at least one in its lineup. Sure, they might be fast in a wind tunnel (some less than others, we found), but aero road helmets aren’t just about speed. They still need to be well ventilated – at both high speeds and low – lightweight, comfortable and hopefully reasonably priced if they stand a chance of being your primary day-to-day choice.

So which one is the best? We evaluated nine of the top models to find out, based on the following criteria:

Aerodynamics

The appeal of an aero road helmet is its promise to help you go faster with the same amount of effort. We tested these helmets at the FASTER wind tunnel in Scottsdale, Arizona – the same tunnel Giro used in developing its highly acclaimed Synthe – at yaw angles of 0, 5, 10 and 15 degrees, and with a single head angle. Recorded values were averaged for a final composite score.

Instead of using the industry-standard 30mph wind speed, though, we tested at 20mph. Higher speeds might very well exaggerate differences in aero performance, but according to FASTER’s director of biomechanics and technology Aaron Ross, you can’t predict airflow on a linear scale. We experimented with a few of the helmets at 30mph and the rankings actually changed slightly.

Most importantly, cyclists don’t spend all day riding at 30mph. We asked the folks at Strava to pull the average speed of its entire, massive rider database to get a real-world idea of how fast we’re really going. As it turns out, male cyclists ride at just 15.6mph on average; for women, it’s 13.4mph. Even if you assume that the typical aero road helmet buyer moves faster than that – say, in a racing situation – we decided to evaluate these helmets for all-around use since that’s how they’re more likely to be ridden.

Just because it says 'aero' doesn't mean it is. The Specialized S-Works Prevail actually beat three of our aero road helmets in the wind tunnel

Statement from Rob Wesson, Giro Director of Helmet Development:

"Giro appreciates the time and effort BikeRadar put into this story – it’s fantastic that the media is paying attention to aerodynamics. We welcome any outside testing of our helmets, but the results are only significant when done with the same scientific rigor and practice that we ourselves put into testing and presenting results to the public.A few of our concerns:

Set up was not consistent from helmet to helmet. The test pictures show that each helmet had a different taping over the straps. Testing has shown that strapping can effect the aero scores dramatically.

What is the margin of error in the test results? For aero evaluations of helmets, the two main components of error come from the operator assembling the helmet to the head form and the error that the tunnel registers. Multiple setups and tunnel runs with the same helmet at different times in the day need to be done and evaluated to understand the baseline and confirm the overall error. Giro’s extensive testing over the years has found that total tunnel data error is approximately 10g of drag; which means that any helmets whose drag is within 10g of each other are statistically equivalent. The LG Course and Protone both get a 3, the Giant gets a 2, and the Air Attack and Synthe get 1s — however all four helmets are within 9 grams of each other and therefore equivalent. If the calculated error is much higher than 10g then it is difficult to impossible to make any valid aero claims.

Head Form Size not compatible with helmet size. We’ve testing on this headform at Faster and know that it is on the large end of a medium fit. These small size helmets clearly just don’t fit correctly. Since the helmets do not fit the headform, they are raised up much higher than where they would actually be ridden on a consumer. This is a bald headform and therefore could have a massive effect on the aero performance of each helmet versus if it was fitted to the correct size headform.

Failing to use Wind Averaged Drag.Simply averaging the results from 4 angles does not accurately represent real-world conditions. Riders statistically encounter yaw angles of 5º much more often than 20º.

Only testing one head angle. This is too limiting to actual real world scenario. Accurate testing requires at least two head angles to evaluate.

Again, we applaud the effort to do some verifiable testing. We at Giro hope BikeRadar can be part of our ongoing discussions with media and other manufacturers toward the end of designing a universal, repeatable, accurate protocol so that riders can make informed decisions when choosing their next helmet or helmets."