A tale of two cal rides

[turbomentor]

Was hoping I might be able to get Boyd or anyone else to chime in on this one perhaps.

Two cal rides attached that yield different results...just wondering what could be going on? One cal ride was conducted using coast downs, the other with a DFPM.

Coast Downs DFPM
WSF 1.359 1.359
Aero .487 .329
Frict 3.838 7.617
Tilt -.1 -.1
CdA .358 .242
Crr .00352 .00796

Interesting yes?

[coachboyd]

Was this done in the hoods? If so, then it looks like the coastdowns gave you better number than using the DFPM. One thing I want to check, this was a power tap, correct? Did you make sure zero the torque before doing the out and back ride? If you power tap was reading a bit low then that is what would cause the iBike to give out a lower cda (because it's all based on the power tap numbers).

Of course, if the power tap was low, the profile made by the power tap numbers would compare better to the power tap file than the coastdown numbers.
By the way, if you select the box that says "road tires" it'll adjust the crr for road tire conditions (based on the closest crr) and will correct the cda, but that is still low in this case I believe.

[turbomentor]

Was this done in the hoods? If so, then it looks like the coastdowns gave you better number than using the DFPM. One thing I want to check, this was a power tap, correct? Did you make sure zero the torque before doing the out and back ride? If you power tap was reading a bit low then that is what would cause the iBike to give out a lower cda (because it's all based on the power tap numbers).

I believe Todd rode this profile on the hoods, and I agree that the coastdowns gave better numbers. Yes, this was a PowerTap. Unsure if he did a zero Torque before doing the cal ride.

Of course, if the power tap was low, the profile made by the power tap numbers would compare better to the power tap file than the coastdown numbers.
By the way, if you select the box that says "road tires" it'll adjust the crr for road tire conditions (based on the closest crr) and will correct the cda, but that is still low in this case I believe.

If the PowerTap was properly zero'd, then how could we account for the same cal ride giving way different readings? To me, it looks like the PT is giving out whacky data, but I could be off base.

[coachboyd]

If the Power tap was properly calibrated, then the numbers from the cda and crr should be looking more like the results from the coastdowns. There is nothing that the iBike can do to fix this, if the numbers that go into making the profile are not good, then the numbers coming out of the profile will be no good.

I remember I had the same problem with my Quarq before I sent it back to the factory to get recalibrated. My cda before I sent it back was always around .330, after I got it back my cda went down to .318 and that's where it stands today.