Thursday, August 23, 2012

The Wind Tunnel: Revisited

Our age is informational.  An infinite library, it gives us every shade upon the entire spectrum of ideas from which to form our opinions.  It is no wonder then, that we live in an age radicalized by confirmation bias.  We seek evidence to support our hopes, rather than use the most reliable evidence to form well informed opinions. 

Through a similar twist of reverse engineering, cycling manufactures can seek out data and tests in order to confirm their hopes—that their products are fastest, lightest, and just plain better than everything else.  Kudos to Mavic then, for, at least somewhat, throwing that idea out the window.  They nudged it very close to the edge of the window sill at the very least. 

Mavic invited independent journalists to San Diego’s state-of-the-art low speed wind tunnel with a challenge.  “Bring any wheel and tire combination on the market and we bet our new CXR 80 wheel set will beat it.”  A gutsy challenge to say the least. 

Unfortunately, Off the Rivet is not yet a nationally recognized powerhouse media outlet (surprising right?), so I wasn’t invited out to San Diego for the testing.  You can read about the whole test on here. 

The wheel that inspired the challenge.  And lived up to it as well.

Several weeks ago, I wrote about what I thought of all of the hype that comes by doing wind tunnel testing (if you haven’t read it, please do, here).  Not to give myself a pat on the back, but I think the point I was trying to make holds true again here. 

While the test is favorable to Mavic, the difference doesn’t really jump out until you get into some pretty serious crosswinds.  That still a considerable accomplishment for Mavic though, considering the hyper-competitive state of aero R&D these days.  Even gaining a marginal improvement is something any company would love to have.  Let’s take a look at the data:

Notice that from a direct head wind all the way until a 10-degree cross wind, the wheels perform almost identically.  Also notice how much difference there is between the data taken from the drive side to the non-drive side of the bike.  The Bontrager wheel actually outperforms the Mavic CXR 80 on the left side.  What this says to me is that the bike is a major contributing factor to the performance of any wheel in a wind tunnel.  What works well in one bike may not in another. 

The cross-section of Mavic's new CXR 80 uses a small removable rubber piece to smooth the transition from tire to rim.

We could take this one step further.  What works well for one person’s position might not work as well for someone else’s.  Check out the test that the author references at the bottom of the article:

Test subject A was what we’ll call a “semi-aero” titanium frame with slightly ovalized tubing, but nothing extreme. Test subject B was a then-cutting edge carbon aero frame. Sans rider, the frames showed a fairly significant difference in drag (the carbon frame would cut about 50-60 seconds per 40k at 25mph). However, when a pedaling rider (Kevin) was placed on each bike, there was no measurable difference in the two frames. Zero, zilch, nada.”

Now I can’t vouch for the dependability of this test, but it was done at MIT.  They’re somewhat knowledgeable when it comes to science, so I think we can give at least some attention to the conclusions to which they came. 

To me this all points to one conclusion.  Not that aero is bunk, because it certainly isn’t.  If there was a box-section rim in this data you would be able to see just how much of an advantage aero-wheels offer.  Rather that the aero playing field has been, at least somewhat, leveled.  Put your purchasing decisions in context—the context of you—to get what is really best.

I get asked all the time “what advantage does aero wheel X give me over aero wheel Y?”  That is a difficult question to answer, because as we have just seen, they are all pretty competitive.  You are far better off to base your decisions on a multitude of other factors like price, aesthetics, compatibility, durability, craftsmanship, or ride quality rather than wind tunnel data.  Take it with a grain of salt. 

The biggest factor in all of this is you.  You are the largest variable, and your ability to pedal a bike quickly is what makes the biggest contribution to getting results and getting faster.  Buy your equipment based on what works best for you, for your bike, or for your pocketbook.  Instead of using this age of information to seek out what you want to hear, take a look at your situation—not a wind tunnel test—and draw your conclusions from there.  

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