Cd*A testing the Giro Air Attack helmet

[Jim Parker]

I've been meaning to do this for awhile. With Calvin's Challenge (a 12-hour race in Ohio) coming up in one week, I figured I better get around to it. I used R. Chung's method and his cool app as a poor man's wind tunnel. You need a power meter, a circular course where you don't have to touch your brakes, and some Excel spreadsheet skills to do this. The more windless the day, the better. The real enemy of accurate results isn't the wind, but the variability of the wind. I didn't have a perfect day for testing, with variable winds of 6 to 11 mph, but it could have been worse. Also, my power meter has been reading high lately, so the Cd*A values might be higher than otherwise, but what is important is the comparison from trial-to-trial on the same day. Here is the data I collected and I'll discuss the results below:


In Trial A I was wearing a helmet with a large rain/sun visor attached. In Trial B, I switched to a standard Bell helmet without a visor. In Trial C, I switched to the Giro Air Attack helmet with the visor up, and in Trial D, I moved the visor down over my glasses.

This is the Giro Air Attack helmet, with a megnetic visor.


What I concluded is that the Air Attack helmet is no better and no worse aerodynamically than a standard helmet when the visor is up. But whe the visor is down, as in the photo, I averaged about a 0.01 improvment in Cd*A. That's very good.

Now if you are curious about the the other results, read on. What does "frame taped" mean? Well, I was talking with Gary Christopher at Bike Sebring in February. With his temporariliy lame foot, he couldn't race, so he must have had extra time time to stare at the Vendetta. He says, "hey Jim, why don't you guys enclose the space under the seat where the seatstay and chainstay tubes run? It'd clean up the airflow even more and give some low storage space." That thought has been banging around in my head since then, so today I very crudely closed off that space with packing tape.

This is what it looked like. Then I took it out on the course for Cd*A testing.


I calculated an average improvment of 0.007 in the Cd*A. Considering how crudely this was done, that's pretty good.

The other variable that I accidentlly tested: forgetting to zip the top on the tail bag. To take the above photo, I pulled my cell phone out of the bag and didn't zip the bag back up until I though all my testing runs were over. Then I saw the bag was unzipped, zipped it up, and did one more run with it zipped. I calculate that forgetting to zip the bag cost 0.009 Cd*A.

So here are the final results. I am ascribing the variability in the results to be due to wind variability and the relatively short (1.5 mile course) course I was using.


I don't claim that they are statistically significant, but they followed very closely to what I expected. It's enough for me to wear the Air Attack helmet with the visor down next week.

Jim

 

[battleaxe0]

From a rather hot zone, on a 96 degree, 90% humidity day, how does the Giro helmet perform cooling wise? My helmet has the biggest openings I could find simply because the August heat here is beastly. Michiganers have been known to melt to the pavement and can't be scraped off until our 2 days of actual winter temps.

 

[ratz]

Don't know why but with its tiny vents the air attack has one of the best air flows inside the helmet that I have experienced it is shockingly cool in the heat. All the riders in these parts that wear them say the same thing when I ask them..

 

[Rick Youngblood]

Don't know why but with its tiny vents the air attack has one of the best air flows inside the helmet that I have experienced it is shockingly cool in the heat

I have one too, but haven't used it in extreme heat yet. It gets pretty hot here in the summer time. I've read reviews on this helmet that says the same thing Bob says, something to do with the design of the air-ducts and how they direct the flow across the top of the scalp.

 

[battleaxe0]

On the frame tape, would taping up the front triangle help any? This is difficult because of needing to pass the chain, but it looks doable to a guy looking at internet pics.
Is there enough clearance to tape from the top of the seat stay to the rear axle, and would that help any?

 

[ratz]

Also, my power meter has been reading high lately, so the Cd*A values might be higher than

Jim,

These numbers look spot on the mark.

I have a test file from about 4 weeks ago that I captured at night with little to no wind. That was on a Vendetta 2.0 and using the same helmet, my rear bag and bottle setup which is about the same size as yours as far as sitting "behind me" in the wind shadow. My data was also captured with a Stages meter. The Cd*A I got was 0.255 on data from 8 runs under Cd*R of about .00395 calculated in Golden Chetah with Chung's algorithms. I grabbed the data and threw it in the web version just now and also get Cd*A of 0.255. Given that my course is just "ok" and I blew my lines a couple of time. Your 0.245 looks really solid.

 

[trplay]

My experiences with the Giro in the Georgia heat is it cools as good as any of my other helmets. The problem I have with the Giro Attack helmet is the dang visor doesn't drop far enough below the nose so the laid back position of the Silvio gives you a crappy eye sight line because its half through the visor and half not. Sure I can tuck my chin for a 10-20 mile ride to get a clear view but any distance and it's a major pain for me. I would assume it will be even worse for me on the Vendetta.

 

[Jeremy S]

I tried the Air Attack helmet and I couldn't get it to fit comfortably with my Silvio head rest, it pushed the helmet awkwardly far forward. I also found it to be significantly warmer than my Bell helmet. YMMV.

 

[Jim Parker]

My experiences with the Giro in the Georgia heat is it cools as good as any of my other helmets. The problem I have with the Giro Attack helmet is the dang visor doesn't drop far enough below the nose so the laid back position of the Silvio gives you a crappy eye sight line because its half through the visor and half not. Sure I can tuck my chin for a 10-20 mile ride to get a clear view but any distance and it's a major pain for me. I would assume it will be even worse for me on the Vendetta.

That's a good point. I noticed the same thing. It doesn't bother that much, but it would be better if the visor came down an inch further.

 

[battleaxe0]

Something else I thought about on the tape - if you had a rear disk, how much difference would the frame tape be? I'd guess not as much as expected because what the tape may be doing is giving you an immovable disk-like area.

 

[ratz]

That's a good point. I noticed the same thing. It doesn't bother that much, but it would be better if the visor came down an inch further.

I imagine the shape of one head comes into play. I can see it not working for some people.

I added the thicker insert padding to the back of the helmet; and thinned up the one in the front and then I'm sure I'm probably wearing it rotated a bit (about ½ inch rotation) forward on my round head versus the actual design. However, having crashed with a helmet enough times now; I understand that because of the looseness of the helmet on my head; it's going to shift around while I'm heading to the ground so I'm not going to sweat having it rotated forward a bit; most of it's protection is going to come from going down side ways and not whiplashing the side of my head into the payment. If I manage to go up and over the front of the Vendetta or the Silvio I'm in for a world a hurt no matter what.

I've take to wearing transition riding glasses. So if I'm not blasting along I can put the visor up and just ride. If I get into big descents or heavy wind I can put the visor down and the sun glasses will fade to clear so that I'm not get getting the double tinting effect. Could use to get the clear visor for mornings the tint one is too dark until the sun is good and up.

The Helmet is also a good match for normal Ski googles which is nice in late fall and early spring.

 

[MrSteve]

The Giro looks awesome... and your numbers confirm it.
Directing the airflow across your scalp is much more efficient than just
poking a lot of slick looking vents all over the helmet, especially when
the helmet is moving through the air.

In the humid, still Summer air, I was overheating and flirting with heatstroke.
So I modified my Walmart helmet to efficiently direct the slipstream across
the top of my head, in hopes of cooler/safer riding.

It worked and it works.
It's no slower than stock and it may well be faster than stock.
All I know is that overheating is no longer a worry and I feel no difference
in drag at speed.

By the way, the mod. was meant as a proof-of-concept prototype and
is paper mache and water-based paint, but it works so well and
was painted by my graphic-artist girlfriend.
So, it's a keeper.

[/URL][/IMG]

My Summer helmet is posing on a polished stainless steel garden globe
-which is brighter than I am-
and you're looking at the intake or the front of the helmet.

 

[John Dorlon]

That's a good point. I noticed the same thing. It doesn't bother that much, but it would be better if the visor came down an inch further.

I tried on an Air Attack in the store. I didn't have my bike with me, but I tried to imagine wearing the Air Attack while reclined on the Vendetta and came to the same conclusion - that the visor didn't come down far enough. I wasn't thinking about line of sight, but it did seem like there would be a lot of wind coming up under the visor.

I will say though, it was a very comfortable helmet, and I'm thinking that I could probably get away with less sunscreen on my face due to the visor keeping sun off of more of my skin than sunglasses would. Hm...might be worth a try...I wonder what the return policy on helmets is....

 

[ratz]

it did seem like there would be a lot of wind coming up under the visor.

Surprisingly that's not the case. I thought it would be too, but I think the air deflecting off your upper body gets it flowing up and over soon enough, never really noticed any challenge there going down hill at 25+ mph..

. I wasn't thinking about line of sight,

That is the main issue; if you head is back or you can't bring the helmet a tad forward that could be tiresome real fast.

There's also two different adult versions; the SuperFit and the Universal. I'm using the SuperFit; as the universal just didn't sit right on my head. Advantage of being in the metro is the big bike shop had 20+ in inventory to try.


EDIT: Before it gets lots in the trees. The Air-Attack comes in two versions; the Air Attack Shield and the plain Air Attack. They are $40 MSRP difference in price. Which is the cost of the Shield if you buy extras. You can't add the shield to the plain version but you don't have to use it on the shield version other than the magnet holes it's the same helmet. The non shield version is a fine helmet all by itself especially for the cooling. If you think you might use the shield get that version. If it doesn't work for you; you can always put the shield up on ebay someone with a broken or scratch one will likely scoop it up pretty quickly.

 

[John Dorlon]

That the main issue; if you head is back or you can't bring the helmet a tad forward that could be tiresome real fast.

I think I might be alright then. My head is angled pretty far down when I'm on the Vendetta - I think because I'm short and I'm a little lower on the headrest than what I should be. I 've noticed that I always have the "double-chin" effect whenever someone takes my picture when I'm riding.

I knew about the Shield and non-Shield versions, and would definitely go with the Shield. The SuperFit/Universal is news to me, though. Thanks for that. I'm not sure which one I tried on. I guess I ought to take my V to the bike shop and try them both before I buy.

 

[battleaxe0]

The Giro looks awesome... and your numbers confirm it.
Directing the airflow across your scalp is much more efficient than just
poking a lot of slick looking vents all over the helmet, especially when
the helmet is moving through the air.

In the humid, still Summer air, I was overheating and flirting with heatstroke.
So I modified my Walmart helmet to efficiently direct the slipstream across
the top of my head, in hopes of cooler/safer riding.

It worked and it works.
It's no slower than stock and it may well be faster than stock.
All I know is that overheating is no longer a worry and I feel no difference
in drag at speed.

I didn't wear a helmet til last year after a bike accident where I broke my collarbone and landed with my head near a tree. I researched and found this Specialized helmet:

That scoop in the front under the reflective tape made quite a difference compared to some other helmets. I doubt it's particularly aero, though.

The furry things on the straps are cat-ears, which work rather well for blocking wind noise.

 

[ratz]

The furry things on the straps are cat-ears, which work rather well for blocking wind noise.

I love those; the new elite ones are tiny and work about 80% as well as the classics you have in that photo.

 

[hurri47]

I rotate the Attack forward to keep my normal glasses from touching the shield, which I figured was asking for scratching if not popping the shield off altogether. The end result is the tip of my nose is only slightly exposed and I can definitely use less sunscreen. Sight lines are not an issue on my Silvio 1.0, but the helmet also works on my lowracer where I lean back on the headrest nearly all the time - still looking through the lens instead of under it.

It hasn't gotten really hot in southern Arizona yet, but I swear the Attack cooling is better than if I wore no helmet at all. There is noticeable cool air flow over my head.

-Dan

 

[battleaxe0]

Another question - does the shield fog up when riding on a super-humid foggy morning? I haven't found anything that stops my glasses fogging over, so this could be an interesting way to fix that if it worked.

Also might be able to skip the Halo since there are a lot fewer holes.

 

[battleaxe0]

I love those; the new elite ones are tiny and work about 80% as well as the classics you have in that photo.

I'll have to look into those. Mrs. Axe often comments on my Elvis sideburns. She tried them, agreed they worked, but couldn't bear the price of having sideburns