Garmin Edge Power vs. ISAAC Power

[SilasGreenback]

The answer to this may be “garmin issue not ours” but using my edge 1030, over a couple of hours ride i get an avg power displayed, recorded in connect and the garmin fitness environment as around 220 watts. However, when i dump that ride into ISAAC said rides are usually on avg 20 watts lower at around 200 Or less. Thats a massive difference. TBH almost too big to be acceptable.....For me its nearly 0.3 watts per kg so feels like i’m kidding myself when garmin is giving me my fitness coaching etc.

Similar story on max power. Garmin says 730, ISAAC 680.

My powerpod is set to dynamic power smoothing and the garmin to avg ignoring 0’s.

Any ideas on where to start or is it “that’s Life?”

[SilasGreenback]

Ahhhh.....calibrate sensor......

Now lets see what happens....apart from garmin most likely downgrading me and my fitness!!!

[lorduintah]

The next thing John is going to want is a ride file.

[SilasGreenback]

Will see what happens tomorrow now i’ve calibrated the sensor and if different get a ride file posted.

Read something similar with garmin and powertap but seemed to be BLE/Ant+ and bluetooth causing problems but same sort of quantum higher on the garmin.

I’m connected to powerpod as a “number“ rather than named sensor which i think is the Ant+ connection. Hope its just calibration

[Velocomp]

There is a small but crucial difference between Garmin max power and Isaac max power.

If your ride file is 100 miles long (as an example) Garmin will report as Max Power the highest number it recorded for a 1 second period.

Isaac reports as max power highest the average power recorded for a period of 5 seconds.

Why the difference? Because Garmin's Max Power is meaningless...their Max Power number is the highest value recorded for 1 second. This number could be an erroneous reading, or simply a fluke.

Isaac's Max power over 5 seconds is representative of the power produced during a portion of a hard sprint. It means something...

Average powers should be close...assuming your Garmin is set so that it includes periods of zero power in its calculations. When zero power is excluded, the average number doesn't mean much.

[lorduintah]

The biggest impact I see on my own calibration of a P3 is tire pressure.

I have set the pressure at 60-psi and ride for a few days - over essentially the same route. Reviewing the day's ride and analyzing the calibration may gradually show the factors shifting

I then pump the tires back up to the original setting and there is virtually no change from the original calibration. (All on essentially the same out/back route - distance may vary.)

So, essentially a leak rate in the tires from 60--psi down to say, 30-psi - and never altering or accepting any suggested changes - then refilling and going for another ride with nearly the same tire pressure results in absolutely no need to change the calibration factors - even the wind scaling.

The implied fact that the degradation in tire pressure impacts a calibration is not surprising at all. First, the rear tire I have loses a bit more than the front - so the tilt shifts. In so doing the perceived rolling resistance will also change as more or less tire is exposed to the road surface. My weight and body dynamics are essentially constant with the way I ride and vary my position over the course of the ride, but will average out over the entire ride. I do not ride in an area where I face gale force winds, but typically breezes, and from mostly the same direction - headwind or tailwind.

I do not usually remove my PP3, so the angle of attack or the wind port does not vary much and temperature variations/weather conditions are not making any impact, while there are variations in atmospheric pressure - that's just weather.

This all tells me that the calibration of this power meter, done with any kind of care (i.e., follow the directions) leads to a meter that is reproducible and reliable. Most anomalies that some see are more than likely due to operator error or careless control of the device.

Do I expect the same power value at exactly the same GPS point on a day-today comparison - absolutely not. I do not ride that way and I am not sure amany are likely to do that.

[SilasGreenback]

Average powers should be close...assuming your Garmin is set so that it includes periods of zero power in its calculations. When zero power is excluded, the average number doesn't mean much.

I can live with the max power being boulderdash as i dont (yet) pay much attention to that. Trying to use power to “reign me in a bit”. And get a better feel for training at the right level. I have a stupidly high heart rate that avg’s 160 on aN easy steady ride and if pushing it i can max at over 200 with avg going up not a huge amount. And at 43 thats a big jump from “theoretical max”. Been like that since i was knee high to a grasshopper and still here so not overly worried. But makes any sort of HR based training hard.

Relatively new to power training your last point is interesting for me. I’d (maybe mistakenly) assumed to set computer to exclude 0’s so that could be the big difference. I’d recon there’s not much time i dont pedal But enough to skew it. Will change that in my computer too and see what happens.

ATM i dont care whether PP3 says 200, garmin would say 220, Powertap would say 180, just want consistency relative to me alone. And to understand power!! Definitely not plug and play like speed is
Thanks.

[SilasGreenback]

Much closer.

Tinkered with the edge settings:
Turned off dynamic data recording and set To 1s
Calibrated before leaving - now got it set to prompt me.
Include 0’s in garmin avg.

Result = garmin 205 avg. isaac 202 avg.

Power was less spikey on the garmin display and “felt” More realistic of my effort. Out on Friday into a blasting headwind i backed off and the power kept climbing. Felt all wrong. Today, felt like i worked and power went up, felt lime i backed off and it went down.

Thats good enough for me