I recently purchased a pair of single sided Garmin Rally SPD pedals that I could move between my various bicycles. I also use a dual sided stages (crank arm) on my Road bike and single sided stages (crank arm) on my Gravel bike. I recently did a ride on my fixed gear bicycle (not single gear actual fixed like a track bike) with the Garmin Rally SPD pedals and after that ride my FTP jumped 31 watts! Thinking about it I think the Garmin pedals might be counting both the push and pull on the axle as “power”??? because 31 watts seems like a lot. That said it now has messed up my XERT as well as my Karoo 2 MPA because every work out I do now (which is 31 watts less) seems like I’m taking it easy. Which then tell me to work harder!! 1. how can I fix my FTP 2. what do you think is going on with the Rally pedals? – side note I have used the Rally pedals on bicycles with freewheels with no massive jump in FTP so they seem to work fine?
It’s a difficult question to answer since we’d need to know how the Garmin Rally pedal power logic has been designed. The back leg can both pull or push. Pushing on the back leg will make you slow down on the track. Also, there is no free-wheeling on the track either so there is always some power. It’s not surprising that you’d see different results with some power meters as there are many “it depends” when it comes to calculating power output.
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Did you calibrate the pedals after you installed it on the new bike? That’s a must. If they self-calibrate, then maybe that function is busted. I use Assioma’s on a spin bike indoors, and swap them for outdoor rides. The spin bike is like a fixed gear, no free wheeling, and a heavy flywheel. I have seen no differences in power. Also consider resetting the pedals.
Edit. I believe even self-calibrating pedals need to be calibrated manually when initially put on the bike. My Assiomas do.
Also…take a look at the DCRainmaker review, under Power Meter Accuracy. On the firmware he was using, there was an inaccuracy involving not compensating for temperature in the way one would expect. Maybe this explains your issue. Garmin Rally Power Meter In-Depth Review (SPD/SPD-SL/LOOK KEO) | DC Rainmaker