Tuesday, July 6, 2010

CdA Analysis

If you followed some of my earlier blogs you'll have noticed my desire to be able to compute my own Coefficient of Drag (CdA) using a Cycleops Power Tap power meter and an iBike iAero power meter.   When these two power meters are combined on the bike you essentially create a "poor mans wind tunnel".  That is, the iAero will calculate CdA with the help of the Power Tap.  These CdA calculations are continuous- in real time on the iAero display.  If you're a Time Trialist or Triathlon with a TT bike I don't have to tell you how invaluable this information is...at least I hope I don't.

In an effort to arrive at some statistically significant data, I figured I would establish a baseline/control position on my road bike first...using iAeros Remote Wind Sensor (RWS).  I chose two positions: 1) in the hoods and 2) in the drops.  I figured I would do at least 10 calibration rides in each positioni with coast downs included.  And, the cal rides would start out at 2 miles rountrip graduating to 4 miles for better accuracy. 

The chart above includes data from my first six cal rides.  I still have four to go for 10 total.  You can already see that my CdA for the "hoods" and "drops" position is almost similar to what analytic cycling.com estimates for somebody my height/weight (5'11"/175 lbs).

When I'm done, I'll transfer the computers to a TT bike and repeat the process by establishing baseline data first.  Then, I can compare different positions/equipment/etc. to see the affect it has on CdA.  The goal, of course, is to find the lowest CdA number without compromising my power output or comfort.

Pretty neat stuff- at least I think so.  Stay tuned for more data/stuff.  Power ON! Coach Rob

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