Do you already own the air attack? Maybe not worth the speed increase. Are you cross shopping an Air Attack and an Aerohead? Worth the upgrade price, but there are plenty of cheaper helmets that are nearly as fast.

I can't find numbers to give you but there's some mention of the air attack in this....

http://forum.slowtwitch.com/...Aero_Camp__P4943130/

Basically, the air attack is one of the worst "aero" road helmets with the best being the evade. But basically any aero helmet is going to be faster than an aero road helmet.

If I had to guess, I would bet the aerohead would test at least 10 watts faster, maybe 15. But everyone is different. I do think it's a safe bet to say the aerohead would be a significant upgrade and far from marginal.

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for me : .009 in CDA between the two (measured at A2)

They post the savings on there website.

Just looking at the aerohead and its shape it is no surprise that the aerohead is fast. The secure reversible shield is a nice feature as well. I have the time savings listed at the bottom of this post of mine.

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I would say that upgrade, for most people, definitely falls into the "good" category. I'd wager in the neighborhood of 10watts or ~1second/km.

No comparison. Aerohead.

Your time savings are based on manufacturers claims ?

Based on multiple tests done with the 2, including A2 testing, the Aerohead would save me 38 seconds on a 40km TT. At IM watts it would save me 3m12s

That data is from the manufacturer.

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They claim
14g of drag difference (1699-1685)
9 watts (15-6)
and 5 seconds difference on a 40km TT at 400 watts (8.4-3.4)

Am I still hungover or does that seem odd ?

To be honest, I hadn't given that first column much thought. I am not even sure what the measurement is but it certainly doesn't jive if we assume that 50grams is about 6.5 watts at 30mph. That isn't even a body on a bike, the grams of drag is far too low, unless the speed is not 30mph. I think the important thing is the shape (just looking it at) + all the data points of other riders testing on their own + the manufacturer claims. Given those I can't see how anyone goes with any helmet but the Aerohead.

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Well, someone at Giro should fix that chart because very few people can relate to the column on drag.
People will get all excited when they see 15w (which is BS in my opinion) but they will look at the 25seconds over an IM and say it's not worth being 22% warmer.
Maybe I'm not reading their chart properly

To the comment on "any helmet but the Aerohead", yes if you are buying a helmet why not pick the fastest to start with (all prices being around the same). But if you have one of the other "better" helmets your $xxx may be better spent elsewhere.

PS : good luck at MT70.3

Thanks I won't be racing MT70.3 this weekend. I am taking a little break after getting sick on Saturday before Raleigh. As far as the chart goes, yes I think you are interpreting it incorrectly. 22% warmer than 99 degrees is 122 degrees. Honestly, I don't know why they put that drag number on there, there isn't enough detail for data geeks to understand anyway, and the average joe doesn't care about grams of drag or watts even, they care about how many seconds it will save in an Ironman.

Saving 25 seconds over an Ironman over the Air Attack is huge and that assumes 250 watts. Age-groupers are not riding 250 watts in an Ironman so you are going to save even more time in an Ironman at 180-200 watts. Regardless you aren't going to find that sort of time very easily or cheaply with anything else and the beauty is that it is testing fast on everyone. I don't think it is an surprise that even the pro athletes are letting helmet contracts lapse knowing that the Rudy Project helmet is costing them 25 seconds. And to be fair we are comparing an aero helmet versus a new aero helmet so gains are smaller but think about people making the comparison of switching aero bike to new super aero bike. You aren't going to get the same value like in the upgrade from this helmet.

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As far as the chart goes, yes the 22% in terms of heat is meaningless

But to go further how meaningless this manufacturer data is, if it's 15w then it isn't 25s on a IM. If it's 25s on a IM, it isn't 15w. Their data doesn't make sense. My testing shows less than 15w and more than 25s. As do other aero helmets.

While the aerohead and AA are the helmets we use the most for testing (for other reasons) I do test 2 other aero helmets and while the Aerohead is faster it certainly wasn't leaps and bounds faster. If you have $500 in your pocket, you will probably be able to get more aero with a A2 and $400 left over for other goodies.