I found some information regarding some of the daft helmets in my previous post HERE. Getting power outputs from this requires a small amount of schoolboy maths, so here it is for one of the silly looking helmets on the market.

**The maths**

Giro have published their drag in Newtons (N) on their website, you can get to it through the following link. Giro Air Attack, then looking at the COMPARE tab. this shows you the difference between the new Air Attack & the established vented Aeon helmets, which is reasonably aerodynamic looking in itself. But if this data is accurate it should give us a good estimate of the power saving that Giro sponsored teams get by using the Air Attack over a standard Giro vented helmet.

The figures are at 25mph or 40kmh, the Aeon has a drag of about 4.2N, the Air Attack approx 3.7N. The drag will increase significantly as speed increases, this isn’t linear, so going twice the speed produces much more drag than a multiple of two, here’s the figures.

**25mph/40kmh**

Aeon: Power requirement is Force X Velocity. 4.2 (N) X 11.176 (m/s) = 46.9 Watts

Air Attack: Power requirement is Force X Velocity. 3.7 (N) X 11.176 (m/s) = 41.4 Watts

So we see that at 40kmh, our pro riders are saving approx 5 Watts of power by wearing a silly hat. Now lets look at what happens when we consider sprint leadouts & other high speed situations at 80kmh.

**50mph/80kmh**

We are not given the drag forces at this speed, so we’ll have to do a calculation to determine CdA, which is the coefficient of drag X area, we just need the value so it can be approximated by using the 25mph figures as follows.

**F** = **CdA** X **p** X (**v** squared / **2**)

F = Force i.e. our drag value in Newtons.

CdA = Drag coefficient X area

p = Air density in kg/m3

v = Velocity in m/s

At 25mph we have F, p (normally approx 1.225 at sea level) & v (25mph is 11.176m/s). So to save you a headache, I’ve calculated CdA as the following.

CdA Aeon = 0.0549

CdA Air Attack = 0.0484

So using the same formula we can alter the speed and we now find that the drag on each helmet is as follows:

Aeon:

Drag = 16.6 N

Wattage required = 16.6 (N) X 22.222 (m/s) = 369 Watts

Air Attack:

Drag = 14.6 N

Wattage required = 14.6 (N) X 22.222 (m/s) = 325 Watts

**Conclusion**

We can see from the above that power requirement is huge at 80kmh compared to half that speed, approximate savings at the lower speed are about 5 Watts, while at the higher speed we see about 44 Watts. We can assume that most sprinters & lead out men require over 1500 Watts. The above calculations are solely for the helmet, not the total power requirement, so we can see how a series of so-called ‘marginal gains’ will produce a few watts here, a few watts there and you see why the sprinters & lead out men are using any aero benefit they can to deliver their sprinter to the front at as high a speed as possible. Also bear in mind that these are all estimates, but likely not particularly far away from the actual wattage savings. As I said before, silly hats are here to stay, in fact they may get even sillier until the UCI steps in.

Blog Summary 2 « spokeydokeyblog[…] 02/04/13 Giro Air Attack Data : Some calculations to see how much advantage the pro’s are getting from these daft helmets. […]

benwasnt an issue for Sagan vs Gilbert !

boHow did you calculate the CdA ?

spokeydokeyblogCalculation method is in the blog.