Without going to the wind tunnel you would be absolutely nuts to ride the A2. DD can probably give you the exact stats but back in the day the Aerohead was winning in like 8-9/10 over the next best helmet, which was likely not the A2.
Actually, this is what DD said. I can’t figure out how to link the post but this is what he said in 2016
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there are a few rules of thumb to keep in mind if you’re not going to test.
Go with the helmets that seem to work the best for the most number of people and avoid the helmets that seem to work the least often. The helmets that work most often are the Giro Advantage 2 (top 3 helmet about 90% of the time) LG P09 (top 3 helmet about 85% of the time -although when this one is bad it tends to do worse than the Giro A2). The new Giro Aerohead seems to be doing really well for most of the tests that I’ve seen, although I’ve only tested it on 1 person and it wasn’t that great.
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yes the Aerohead tests well but it is not head and shoulders above the P09 or even the A2. Very questionable if he can’t buy more speed elsewhere with his $250. And let’s not forget the visor vs sun glasses discussion.
It tested head and shoulders above the P09 for me fwiw. I also had an A2 previously. From the others I was with at a wind tunnel or with data it performed extremely well too. From a design perspective it isn’t hard to understand that it was designed as a helmet while the Giro Aerohead was designed as a system, face shield + helmet. It was really the first face shield IMHO, that was designed with aerodynamics in mind. Given the MIPS technology alone, that would be a reason to spend the $250. Your noggin is priceless. The aerodynamics are just free at that point.