Image stolen from their site because inevitably the site will change.
A while ago I started thinking of aero road helmets. It started a long, long time ago when someone (Cannondale? Specialized?) tested a couple riders and a slew of helmets in some wind tunnel. It was probably in the early/mid 90s since they were testing foam-and-mesh helmets as well as the "new" plastic shelled ones. My take away from that presentation was that a rider's posture/body makes a huge difference in selecting an optimal aero helmet. In the case of the presentation one of the riders (he had a shorter neck) was most aero with a normal, slightly tailed road helmet. Other riders, with longer necks, tested best with proper aero helmets.
Regardless, a rider's helmet (and head I guess) create a tremendous amount of drag and is a place to gain a "secret" edge. These secret spots give you a chance to make subtle but significant changes, sometimes making quite a difference in performance. This is especially true, relative to other racers, when the others get distracted by other aspects of your gear. In car racing such "hide through distraction" works really well - a team will carefully cover its "secret" design wings and such when in fact their performance gains come from elsewhere, like a floor design or something. The other teams, seeing the wings get covered, expend a lot of energy photographing the wings, examining just what makes them different from theirs (made more difficult because they're not that different), and after countless hours of analysis will say, "Daggummit, they led us on a wild goose chase."
For me, too, I tried to use any advantage I could through equipment choice.
It started with the Cannondale frames in the mid-late 80s. As a big gear stomper, especially in sprints or up short power hills, I felt the Cannondale frames gave me a huge advantage. I know I would climb in at least one cog smaller, and I knew I could jump as hard as I could and not make the rear derailleur shift.
See, in the old days frames were really, really flexible. One of the "flex tests" was to jump/accelerate really hard while you were just riding the bike. If the frame flexed enough then the rear derailleur cable would loosen (the cable would literally hang limp) and cause the derailleur to shift into the next cog inadvertently. Magazine reviews would talk about "... and the bike wouldn't shift up no matter how hard I sprinted". The Cannondale was stiff enough that such nonsense was never an issue.
I used other equipment choices to my benefit. For many years, before any shift/brake lever integration, I raced with a right side bar end shifter. This allowed me to shift rapidly during a sprint, giving me an edge over my rivals with a normal set of downtube shifters. I could jump in a low gear and sprint in a high gear, the best of both worlds. Others would debating jumping in a bigger gear (in order to max out top speed) or a lower gear (to get a better jump). Sadly, after STI came out, guys I could regularly beat became untouchable - my equipment choices had given me a huge advantage in this case.
I also used super light Aerolite pedals, 38 grams each (with cleat and hardware), 76 grams for the heavier steel version. Combined with a lightweight and super stiff wood soled shoe (criticized for being "too stiff"), I had a super light shoe/pedal weight. Although I never had a definitive "test" like with the shifter in the previous paragraph, I can tell you that when I finally went to a normal pedal it felt like someone strapped weights to my ankles.
I also adopted aero wheels in the early 90s, racing frequently with a rear disk wheel and front TriSpoke (aka HED3). Given the chance I rode on a pair of TriSpokes. When Zipp came out with their first rims (the 440 and 340, precursors to the 404 and 303), I used them as well. Nowadays everyone uses aero wheels - my 2 or 3 mph advantage at top speed disappeared. Interestingly enough I no longer sprint the fastest. I mean, okay, I'm getting old and stuff, but it used to be ridiculous, me on TriSpokes and everyone else on 32 spoke box section wheels. Okay, if they had "super duper" wheels they'd be on 28 spoke versions of the same.
And, because I felt aerodynamics really helped with the bike, I'd take other approaches to reducing my overall drag. For example I know that the body is the least aerodynamic part of the bike racer unit. Therefore I worked on reducing my own drag as much as possible, through posture and equipment.
I used Scott Rakes whenever I felt fit enough to justify putting them on the bike. They gave me a super aero position with my elbows close together. I tried other aero bars too but found them less helpful - the Spinaccis (kind of short aero bars but illegal for USCF use), the copycat 3ttt product, some bar that connected the drops (think of a towel bar connecting your two brake levers), Scott DropIns (the end of the drops had extra tubing that turned inward). All had their disadvantage for me - the Spinaccis were more TT than sprint, the bar that connected the drops were unwieldy to use, the DropIns put my hands too far back.
Nonetheless I understood the importance of taking advantage of these things. The Rakes were always close to the surface of my "extra parts" box and they went on whenever I thought I'd need to chase (bridge to a break or just chase after getting shelled).
Note the Zipp 340 wheels and the Scott Rakes (the "extra" bars at the center of my normal bars).
Note also that no one else has aero stuff.
Final note: the Zipp 340 wheels weighed the same as my slightly higher spoke count 280g rimmed wheels, so they were light too. Most riders at the time were running 400g rims, 28 spoke up front, 32 spoke in the rear. I ran either the 28 spoke 280g rims or the 24 spoke Zipp 340s (which were about 320 grams). They were quick on acceleration and gave me about 1 mph more top end. By now everyone is using a brake/shift lever so no more advantage there.
In the picture above Keith Berger, for whom the Keith Berger Crit is named, is on my wheel. He was still a Cat 3 at the time and he won the 3-4 race (the picture was taken during the 1-2-3 race). Keith launched when the field was already at its limit, bridged to a break, and won the sprint. It shows that even with equipment it doesn't matter if you're not able to use it. I won the Series either the year before or the year after, mainly through the sprint. In that particular year's Series I removed the Rakes after this first week - I had enough teammates to chase things down so the Rakes became unnecessary.
Along those lines of "subtle changes" I sometimes taped the vents closed on my old Giro Air Attack, reducing both the ventilation (when temperatures plummeted) and decreasing drag. Later I did that to almost all my helmets, usually for the Bethel Spring Series races (like here, for example). I used either clear packing tape or, later, black electrical tape. The black tape was more discrete and easier to remove when the weather got warmer.
Eventually I started thinking of getting a helmet that was more aero. I was thinking more in terms of the Bethel Spring Series, a race series normally held in cold conditions. At that point a racer doesn't need a lot of ventilation; in fact, when I did one week with a brand new, super ventilated helmet, my head hurt from the cold air hitting the now-insufficient skull cap I wore under the helmet.
Since I decided that since I really don't want air flow I should be able to get by with a rounder helmet, one more conducive towards my head tilted down sprint position. This would also work on the track, but that wasn't part of my thinking yet.
I contemplated, but couldn't bring myself to wear, BMX/skateboard helmets. I tried them on a few times at a local shop, probably prompting questions about me ("Is he going into BMX?"). I ended up getting such helmets but mainly for my brother. He does skate and skaters fall a lot more frequently than cyclists.
Recently I thought of the ski helmets, with vents you could open and close while you rode. As a bonus they had goggle strap indents in the back, so when it was really cold I could wear goggles to protect my eyes. For me, riding in bitterly cold weather hurts my eyes, and with prescription glasses I can't wear regular eye protection type glasses. As a bonus if I went skiing I'd have a helmet (and at some point I do want to downhill ski again and I won't do it if I don't have a helmet). The problem with these helmets was that with rapidly changing helmet standards I wasn't sure if the ski helmet would be legal for use in a bike race. I nixed the sliding vent closure Giro helmets at that point.
My favorite helmet thus far was one that I couldn't buy locally and I don't think passes the right safety regulations for use in USAC. It's made by Kask and I saw it at Interbike in 2009.
Apparently the helmet was made for commuting. What caught my eye was the built in face shield, a huge factor in the aero-ness of a human head.
I'd have gotten it simply for the cool looking liner inside.
As you can see ventilation is a bit low on the list of requirements. At a Bethel Spring Series race it would be fine, but in 90 degree summer crits this helmet would probably see you head to the hospital after having heat stroke.
Now Giro has a helmet due to be released for 2013. I'm sure we'll see it in action in the Tour and at the Olympics - that's why they "released" it now, so people like me would go, "Oh, cool, look, an aero road helmet!" and talk it up.
I'm such a sucker.
Seriously, though, an aero road helmet is huge. I haven't looked at any stats or anything but I bet that such a helmet will save at least as much as an aero road frame. Okay, probably more. Maybe close to an aero front wheel. Whatever, it's going to be a huge savings relative to cost. At the $200 price point it'll be less than a top of the line "regular" helmet, weigh within 50-90 grams of said "regular" helmet, and probably be worth the same as a $1000 front wheel as far as aero is concerned, and way more than a $4000 frame.
For me that's a win-win so I'm signing up.
Now to wait for the next team Giro ordering window. Hopefully before the 2013 Bethel Spring Series.