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Home Blog 1cm lower bars equals 20 watts: test again and again and..

1cm lower bars equals 20 watts: test again and again and..

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A friend of BTR forwarded on a series of anecdotal information to me the other day.  In this anecdote, a person claimed that lowering their bars by 1cm (keeping everything else the same) resulted in an ~20W decrease  for a given speed (speed not disclosed).  They seem to have attempted to validate this claim with a mixture of wind tunnel data at a reputable facility and their own field testing based data.

(more after the jump)

 

The whole scenario surrounding this anecdote and its history reminds me of one of my favorite books by Michael Shermer: "Why people believe weird things".  One of the chapters late in the book is titled (IIRC) "Why Smart people believe weird things".  The originator of the anecdote at play in this blog entry is most definitely a smart person in certain areas.

 

In the chapter of Shermer's book I make note of above, Shermer makes the statement "Smart people believe weird things because they are skilled at defending beliefs they arrived at for non-smart reasons."

In this specific anecdotal case regarding field test determined CxA, I'd say determining the effect of a 1cm bar height change is tricky business.  Heck, that small of a change is tricky business even in a wind tunnel.  Caveat emptor, folks!

With regards to the 1cm change in bar drop holding all else equal, my experience would suggest an expected reduction in CxA of about 1%...or, about 2-3W at typical TT/Triathlon speeds.

Now, sure, it is taken for granted that there can be some variation in this 1% value, but, yeah, if I personally changed an individuals bar height (holding all else constant - and we have means of making sure all else is as constant as can be!) in the wind tunnel here in San Diego and achieved a nearly 10% reduction in CxA...well, for sure, I'd be testing things again.

Maybe this individual who provided the anecdote under discussion did test things over multiple symmetric changes up/down/up/etc... over multiple days during their data collection, but this doesn't seem to be the track record when making claims based on field tests for this individual.

I'm sure there are plenty of folks, such as Robert Chung - founder of the Chung Method, who would be happy to analyze the raw power meter data and provide their opinion regarding the anecdotal conclusion that was presented to the public.  Placing these raw data in proper context is the tricky part, but I'm sure it can happen!

Uggh, I'm totally dragging things out here...What's my intended takeaway for all of you as I write this blog entry?

Field test with skepticism and care, folks...I wouldn't want all you smart people believing weird things!

 

Last Updated on Wednesday, 23 January 2013 04:04  

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