I have a SRAM Force Powermeter.
I recorded a crit today with my Garmin Fenix 7 and my Wahoo elemnt.
It was a 15-watt difference over 10 minutes. Even for the 40-minute crit, it was 282 vs. 304 avg power.
Both devices include zeros.
I typically record all my rides with my Garmin Fenix, and sometimes, for workouts, I will use and upload the data from my Wahoo, as it has the laps for me to review later. However, I have never bothered to compare or really cared to compare, as I only care what my Garmin says.
But a 20-watt difference from the same power meter is wild to me.
Has anyone had this issue before? What is to be trusted?
Recording with different devices will almost always have this issue when looking at overall power/agerages. It doesn’t surprise me there’s this much difference between a Garmin and a Wahoo device. Even though they’re connected to the same power meter, they’ll each be recording things ‘their way’.
The discrepancies are mostly with the stop/starts. The steady-state (ish) sections look pretty close, aside from less smoothing on the green line in your graph.
This is why I’ll always use the same manufacturer (typically Garmin EDGE) for power meter comparisons. Even then it’s not uncommon to see a few watts difference due to recording averaging/sampling.
That said, if you look at your file, the majority of the differences in the total wattage averages for that section, are coming from the Wahoo not going to zero, while the Garmin is. There are two explanations for that:
A) Some sort of sticky-watt issue on the Wahoo
B) Some sort of drop-out issue on the Garmin
Since it’s a crit, it’s likely you stopped pedaling in those cases, in which case, it’s ‘A’ above, and the Wahoo is incorrectly giving you credit for powers you aren’t putting out.
Like Lama says, most of us that do power meter testing tend to use the same brand units for our data collection (and usually the same generation, e.g. all x40 series or x40/x50 series), so that the codebase is basically the same.
