Newton+ profile

[dtrousdale]

I generally get very different results from my Newton+ as compared to my Quarq on the same bike and on the same ride. I've been using iBikes/iAeros for over 5 years and have set up innumerable profiles, so I'm puzzled why I am getting these differences. I did check my profiles against the guidelines published on this forum, and two do seem out of whack: (1) CdA on the hoods should be 0.28 to 0.45, and I got .589; (2) wind scaling factor for handlebars should be 1.3 to 4.5, and I got 1.125. Everything else is within the recommended ranges. I have no idea what I would do differently to get different CdA and wind scaling numbers as I believe I performed everything correctly.
To get my profiles, I completed about 9 coast-downs and an extra long Cal ride. My understanding is that once I've uploaded the coast-downs and Cal ride, the Newton software will compute aerodynamic and frictional drag coefficients based on the DFPM and iAero data captured during the calibration ride. Also I assumed that the Boyd-in-a-box magic would happen to eliminate further tweaking of the coefficients.
Here are some results from the attached ride file that I find disturbing. I am highly inclined to believe that the Quarq DFPM numbers are more accurate:

Newton
Avg Power - 183.7
Max Power - 980
NP - 232W
IF - 0.85
TSS - 309

Quarq DFPM
Avg Power - 158.7
Max Power - 728
NP - 201W
IF - 0.73
TSS - 232

[Russ]

dtrousdale,

Since it is raining, decided to take a look at your file.
1. Your .0025 Crr is probably way to low. If you raise this in the cal ride analysis, your Cda will become lower.
2. Your power:
At 2:18:36 (35.2 mi): Pow: 314 W; Speed 4.5 mi/h; Wind 7.1 mi/h; Elev 550 ft; Slope 15.3%; HR 145 bpm; Cadence 47 rpm; Gear Ratio 1.21; rec rate = 1 s
Looks ballpark reasonable, gravity being your main component of resistance. Compare it to the Quark there for a sanity check. I did not put the figures into any online calculator to really check, this is just by eye and compares to my one grade nearby that is that steep.

So I bet your biggest issue is the probably too low Crr, try .0055 to .0065 depending on the road roughness where you did the CD's.

Next I extracted your profile from the ride file and tweeked it thus:
CdA: 0.330 m^2; Crr: 0.0060 (a swag, shooting from the hip)
Then analyze with new profile:
Power Avg 158.1 Max 866W which is much closer to your Quark results....

Regards,
Russ