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Tour de Tech: Robbie’s Big Fat Helmet

Can someone please tell Robbie McEwen to retire the Big Fat Helmet™ thathe and his teammates wore during Tour de France time trials? It is physically painful for me to look at that thing. Not only is his helmet just plain dorky looking, there isn’t a doubt in my mind that it is an extremely slow helmet and ultimately is a detriment to his time-trial performance. What would make me say such a thing? Well, I was recently lucky enough to spend some time in the Allied Aerospacewind tunnel where I got to tunnel test some one-piece aero bars.During that entry I also got to stick my long-legged and

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By Kraig Willett

Figure 1 In the tunnel at Allied Aerospace.

Figure 1 In the tunnel at Allied Aerospace.

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Can someone please tell Robbie McEwen to retire the Big Fat Helmet™ thathe and his teammates wore during Tour de France time trials? It is physically painful for me to look at that thing. Not only is his helmet just plain dorky looking, there isn’t a doubt in my mind that it is an extremely slow helmet and ultimately is a detriment to his time-trial performance. What would make me say such a thing?

Well, I was recently lucky enough to spend some time in the Allied Aerospacewind tunnel where I got to tunnel test some one-piece aero bars.During that entry I also got to stick my long-legged and gangly self inthe test section and quantify my aerodynamic properties.

As part of my aerodynamic positioning analysis, I took the time to verifythat my tunnel results were reflective of real-world results. I didthis by conducting a field-test using a power meter, an anemometer (windspeed measurement device), and a known piece of roadway.

Figure 2. The photo studio and Lucho

Figure 2. The photo studio and Lucho

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As one should expect, the “real-world” test showed that my tunnel numbersand field numbers were in agreement to within a few percent. As afinal step in documenting my current position, I also measured my frontalarea using a makeshift photo-studio in my living room. The imagebelow illustrates the importance of making sure your pets – in this casemy dog Lucho (named after the late 80’s Columbian climber Luis Herrera)– are kept confined. This confinement, of course, is necessary inthe name of science…

Thanks to the miracle of a modern digital photo manipulation softwarepackage, it was possible to remove Lucho and my bicycle from the originalphotos in an effort to improve consistency in the results. What wasleft, then, was a bunch of black and white pixels that could be countedin order to determine a frontal area measurement (hint: the inclusion ofa known reference area – that black piece of construction paper hangingon the ruler to the left – is what allows for the final correlation ofpixels to square meters). The images below shows some examples: mystandard TT position with three separate helmet configurations.

When this exercise was all said and done, the frontal area analysisfor the middle image (my standard position and aero helmet) correlatedwell with tunnel measurements using some standard assumptions defined inthe scientific literature with regards to my body shape. After myposition investigation was finished, I had convinced myself that measuringfrontal area was meaningful.

Back to the helmet thing, though: the black and white images should show that the conventional Giro helmet presents a slightly larger frontal area (as the distinct bulge between my shoulders shows in the right-most image above). I would speculate that the head fairings that pro’s in Europe used last year did not significantly increase the frontal area of a well-positioned rider. Furthermore, the streamlined nature of those fairings should have improved rider performance due to the more aerodynamically slippery shape that resulted.

Figure 4. Big helmet on the left. Big Fat Helmet™ on the right

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With new safety standards for TT helmets in place this year, helmetsnecessarily got bigger in frontal area. From the looks of it, theyare nearly as big as a standard helmet, but are, for the most part, morestreamlined. If one makes the precarious assumption that the onlything that changed in the aerodynamic properties of the helmets from lastyear to this year was the frontal area, we should be able to ballpark justhow much slower these new “safe” helmets are during a 40k TT.

The following table shows the results for the three helmet configurationsI took data on:

std- No Helmet
1994 Specialized
1998 Giro
Frontal Area
(M2)
0.316
0.318
0.323
FA Increase
0.002
0.007
Seconds slower
in 40km TT
7
24

Based on a frontal area analysis, it is reasonable to estimate thatthe wrong aero helmet can impact TT performance by around 20 seconds orso. In Robbie McEwen’s case, though, I think the penalty is muchgreater:

…and the updated table:

std- No Helmet
1994 Specialized
1998 Giro
Big fat helmet
Frontal Area
(M2)
0.316
0.318
0.323
big
FA Increase
0.002
0.007
fat
Seconds slower
in 40km TT
7
24
slow

So, who is going to tell Robbie the bad news about his Big Fat Helmet™– you, or me?


Kraig Willett is a product development engineer in the golf industry,a former Category 1 cyclist, and owns/operates his own company: K-dub Enterprises.K-dub Enterprises is the home of: BikeTech Review (www.biketechreview.com),which provides objective laboratory based bicycle product reviews and TheCount, which generates product usage statistics during selected cyclingevents. Kraig can be reached via email at kdubenterprise@adelphia.net orby phone at (760) 723-5839.

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