In Reply To:
Would you agree?
Pretty much, and I
do like your use of analyticcycling to "ballpark" the estimated savings. That said, those aero gains were also basically in line with what my test measurements said they would be in that they were ~2 to 2.5 s/km. That's pretty damned good agreement, if I must say so myself ;-)
Just so we're all "talking the same language", I'll run through a similar estimate and give all the inputs. The main assumptions are that it is a flat course (it's not, but that's OK in doing this comparison) and that the wind conditions were similar (they weren't, but I'd say the wind conditions in 2007 were more favorable...so this will be a conservative estimate of aero gains).
So, in 2007, using the following inputs:
Area = .225 m^2
Cd = 1 (this plus the Area were obviously chosen to make the CdA product the measured .225 m^2)
Air Density = 1.08 kg/m^3
Mass = 84 kg
Crr = .004
Slope = 0
Power = 230W
That results in a predicted speed of 11.64 m/s, for a total time over the 37.1 km course of 53:07
Now, in 2008, the temperature was 20F lower and the barometric pressure was higher, which resulted in the air density increasing to 1.124 kg/m^3. Another temperature effect is on the Crr. A commonly accepted compensation for temp is 0.6%/deg F. This means the Crr would increase to .0045 from .004.
So, if I'd run the
same setup as 2007 and put out exactly the same power, just from atmospheric changes alone (with effects on air density and Crr) the calculator predicts a speed of 11.41 m/s, for a time of 54:03 over the 31.1 km.
That means the course was basically 1 minute slow this year just due to conditions. In reality, I think it was even slower than that due to the slightly different winds, but we'll disregard this since it just makes the potential savings more conservative of an estimate.
OK...I went 1:45 faster on a day that was 1 minute slower....that means my "total" time gain over last year was 2:45. Checking that with the calculator, if I hold the CdA the same and just increase the power, it comes up with a speed of 11.74 m/s, which would be a 37.1 km time of 52:40, or basically 1:23 faster.
So, of the 2:45 of time gain, basically exactly half (1:23) was due to the higher power (just as you found), which leaves a 1:22 gain due to aero changes, or 2.2 s/km. Well, the ROT says that should be equivalent to a CdA drop of .022 m^2, which would put my 2008 CdA at .203 m^2. Hmmm...does that number look familiar?? Pretty close to my measured .205 m^2, right?
If I plug a CdA of .205 m^2 into the calculator with my 2008 power it comes up with a speed of 12.08 m/s, which would be a predicted time of 51:11 vs. the 52:40 with a CdA of .225 m^2...or, about 1:30 faster. That's pretty darn close to the 1:22 difference calculated above, huh?
Now...I know the bike was different (Soloist vs. P2K), but measured CdA of the setup I ran last year was within .002 m^2 of what I measured for the P2K, so it's safe to say that I would've been the same speed on either bike. My position (as measured by the location of the "touch points" relative to the BB) was identical.
The evidence that the vast majority of the aero gain was due to the different frame is pretty damned compelling, if you ask me...
http://bikeblather.blogspot.com/