I have a similar issue with a power difference between Garmin pedals and smart trainer. Smaller difference than yours, but still enough to turn a sweetspot session into a threshold session.
I actually took a different path to @mcneese.chad’s suggestion and decided to quantify the difference as best I could and then just live with it. Basically in the interests of time-saving and simplicity:
- Less time spent switching pedals between bikes (I have a dedicated indoor bike and split my time about 50:50 indoors:outdoors)
- Less time spent calibrating Garmin pedals which is always a slightly erratic process (smart trainer calibration by contrast is bulletproof and mine never seems to need it anyway)
- Less time spent replacing Garmin batteries since they’re used half as much. Especially as I’ve had issues with power cutouts on mine, so changing batteries is a bit of a faff as involves putting drops of baby oil on the contacts to prevent faffing
- One less device and one less connection equals one less thing to go wrong. If you’ve ever spent half of the hour you had available for a workout restarting and re-pairing devices trying to resolve connection issues you’ll appreciate this!
Difference between the 2 power measuring devices seems to stay consistent at different power levels, if they were diverging or converging as the power went up I’d be more concerned that the workouts were hitting the wrong zones.
I guess if you want to be really structured with your outdoor workouts then using same PM for both would make more sense. In my case I do my more structured work indoors, and outdoors rides are either with groups, or things like recovery, endurance or tempo rides where hitting precise power numbers isn’t too critical. Also turns out that I have a higher FTP outside than inside anyway, which almost exactly cancels out the difference between the PMs! This is quite common and likely a result of some combo of more movement on the bike, better cooling and/or better motivation. So if I did use PowerMatch and then did outdoor workouts based on my indoor FTP, they’d likely be too easy…