AeroPod, PowerPod and Newton

So, flat and rolling speed matter a lot to me on a bike. I had wanted to do an unscientific comparison of two bikes I own to see just how much more aero the the aero bike is than the all-rounder bike. I can only have one due to some financial circumstances that were outside of my control (my dog got sick and I would spare no expense to try and help him).

Bike 1 is the aero bike. It has an aero frame, disc brakes, 62mm deep aero wheels. Weight is approx. 8kg ready to ride.

Bike 2 is the all-rounder. It has an aero-informed frame, disc brakes, and ultralight 35mm carbon wheels with some aero benefit. Running the exact same tires as Bike 1 (granted at a somewhat lower pressure). Weight is approx. 7.6kg ready to ride.

On different days (June 3rd and June 11) I did the same rolling 10-mile course with each bike (approx. 500ft of climbing). Clothing was similar, but I was wearing aero socks with Bike 2. Conditions weren't too dissimilar. I did each ride nearly flat out (90%) and was more fatigued on June 11 from doing a number of longer rides recently. Hence, the reduced power. Of note, I actually took a slightly more aggressive position (drops the entire time) on the Bike 2 run, so it should've had a small advantage there.

Here were the stats:

Total Time:
-Bike 1: 26:23
-Bike 2: 27:51
Average Speed:
-Bike 1: 22.7mph
-Bike 2: 21.6mph
Average Wind:
-Bike 1: 22.5mph (-0.2mph)
-Bike 2: 21.2mph (-0.4mph)
Average Power:
-Bike 1: 288.6W
-Bike 2: 270.8W
Normalized Power:
-Bike 1: 302W
-Bike 2: 286W
CdA:
-Bike 1: 72.0*4/1000 = 0.288
-Bike 2: 77.2*4/1000 = 0.3088

Does this seem like a reasonable comparison? How much might deep-section aero wheels for Bike 2 close the CdA gap? I was quite surprised there was this much difference. An extra 18-watts is not closing one-and-a-half minutes over 10 miles.

I would love feedback. There are definitely benefits to the all-rounder (well, one really--the gearing is more appropriate for how hilly it is here).

Attached the files.

This is a really tricky thing you're trying to accomplish with this setup:

1) You have two different bikes with two different calibrations

2) You're trying to do comparisons in profile 3 (profile 4 is much better for precise testing)

3) Your Crr in both bikes was 0.006--high for road tires. The HR/CdA calculations are based on this value of Crr, irrespective of changes you made afterwards (to 0.004)

4) Your wind speed calibrations were slightly different for the two tests. Small differences in wind calibration can cause material differences in CdA

5) The result of the above is that the HR/CdA data isn't good for these tests

Here is what I did:

1) I used the command "Analyze/Return to original Download" to get both files back to the conditions actually recorded during your testing.

2) I used the command "Device/Check Calibration/Use DFPM" to correct the files for differences in wind calibration

3) I used the command "Tools/CdA Analysis" and highlighted the flat portion of the rides to get the CdA numbers for the corrected files.

With these changes I got the following:

6/3 ride, Crr .006, CdA = .307
6/11 ride, Crr .006, CdA = .326

So, it looks like your bike 1 setup is definitely more aero...interestingly, the difference is about 0.019, almost same as your analysis determined.

NOTE: The above analysis does not take advantage of most of the advancements in recent AeroPod firmware. It would be much better if you repeated your testing using profile 4, according the instructions for profile 4.

That helps tremendously. One of these days I’m going to do an actual Profile 4 proper experiment lol.

How is crr determined by AP? For the device setup, I use the same settings. Asphalt with premium clinchers at 85psi. I’m guessing that’s what leads to the .006 crr? Otherwise, wondering if AP is detecting how rough the road is where I do the calibration ride (not super rough, but not smooth either).

AN2019 wrote: ↑Sun Jun 12, 2022 6:30 pm How is crr determined by AP? For the device setup, I use the same settings. Asphalt with premium clinchers at 85psi. I’m guessing that’s what leads to the .006 crr? Otherwise, wondering if AP is detecting how rough the road is where I do the calibration ride (not super rough, but not smooth either).

Crr is determined by tire pressure and road surface type. Your slightly lower tire pressures adjusted Crr up a tiny bit.

You should be OK; the important thing is consistency of Crr between bikes (both bikes have same Crr, which is good).