Awhile ago Specialized released this video during the launch of the s-works evade road helmet:
At about the 1:35 mark a claim is made that the helmet would save 400kj during a 5-hour stage of the tour de france. Sounds like a lot, doesn't it?!? Let's take a closer look at this claim for fun.
For reference, 400kj over 5 hours is roughly 22 watts! => 400,000j/(5hr*3600 sec/hr)=22.2 watts...so that's the claim as I understand it: 22 watts during a 5 hour tour stage. That sounds like a lot based on my experience testing a variety of full-on TT aero helmets in the san diego wind tunnel over the years.
Now, the way it's phrased, there's some wiggle room (is this for a solo breakaway, or sitting in the pack, for example, and there is no speed qualification, etc..), but at face value it is meant to leave the impression that if you are a typical competitor in the tour, you'll be saving 22 watts over 5 hours. It still sounds fishy despite the vagueness, so let's look at some data I can talk about in order to put things into context.
MIT published some aero helmet research an undergrad did about a half dozen years ago: Benchmark of Aerodynamic Cycling Helmets Using a Refined Wind Tunnel Test Protocol for Helmet Drag Research. Google it.
I scraped data from this undergrad thesis where they tested 13 helmets at a variety of beta angles and head positions. They ultimately compared these aero helmets to a standard road helmet. There were no brand/model details for the reference helmet, nor the aero helmets, but big-picture trends could be ascertained. My final analysis looked at two head positions that I deemed appropriate across all beta angles.
avg aero helmet vs road helmet savings at 30 mph -> 16 watts
max aero helmet vs road helmet savings at 30 mph -> 18 watts
min aero helmet vs road helmet savings at 30 mph -> 12 watts
FWIW, this is pretty consistent with my experience at the tunnel here in San Diego. These data pass the sniff test, iow! ;-)
At typical 5 hour tour de france stage speeds (25mph) the MIT data suggests:
avg aero helmet vs road helmet savings at 25 mph -> 9 watts
max aero helmet vs road helmet savings at 25 mph -> 10 watts
min aero helmet vs road helmet savings at 25 mph -> 7 watts
My takeaway on the s-works tour stage claim in the video is that it's misleading at best (and definitely does not pass my sniff test). Not only are they potentially claiming their evade helmet is superior to traditional TT helmets available around 2006/2007, but they also seem to be claiming 2X+ the best case scenario effect during a stage of the tour.
What does your analysis of the MIT data and the s-works evade claim indicate?