You have to test it yourself or you're just guessing.

end of discussion...


sure, but it's all independent


sure but it's very independent data

Ok, given that, how does anyone buy the "right" aero helmet? Or is it all just guess work? Unfortunately I don't have access to a wind tunnel or a large collection of helmets.

That's a great question. It is completely all guess work, as is buying apparel.

For the most part, the answers revolve around "it depends" and "maybe" and "potentially."

So, buy what you like the most.

Seems to me that to provide statistically useful information you would have to test on all manner of people and positions, because any helmet can test differently for any person, and any position. But in doing so the data would be of limited value to any one person and position. You might find some general trends - eg the Giro A2 tests fairly well on quite a few people. But the width of the distribution curve would be such that you couldn't have very much confidence in the data for your personal use, and you might not be typical yourself.

In lieu of being able to afford to take helmets to the tunnel, or alphamantis ever coming to the Manchester velodrome (for me), you are left with testing using the Chung VE method (search "platypus" thread) or simply picking something that appears to mate nicely with your back and fill in the void at the back of your neck. I don't have time for testing (barely have time to train), so I tried a bunch and went with the latter. Hopefully my helmet isn't total crap. Hopefully my position isn't total crap. But I like the colour and the visor makes me look like the dude from Street Hawk.

I appreciate that there are lots of variables when looking at helmets, and as a result it is unwise to give guarantees or definites.
But it's not totally guesswork, some helmets tend to test well and others tend to test less well.

Jim from ERO regularly posts here on things like this. He will give general indications like "if you don't have access to a wind tunnel, then buy either helmet X or Y as they test well on almost everyone".
Yes, he will give caveats such as such as "... but I've also seen it test the slowest of all helmets on one or two people" but it gives the rest of us a starting point when looking round.

While your responses are technically correct, I think you could try to be a little more helpful.

Sometimes answers only beget more questions. Paralysis by analysis is a common thing on ST re: aerodynamic stuff.

one helmet that tested best for one person, tested 24w on the bad side for me. so, quite a range on best helmet for any person

do you have a picture of your position