Depends on its calibration. A couple friends have them, and they seem very good. A couple others have grossly miscalibrated Pelotons that register >100W high.
The consensus I have gleaned is that they can be accurate, but it depends on the owner.
If the power reading on the Peloton Bike is “defined” as the same power we think of when riding our road bikes with a power meter, then I’m thinking this would be an easy comparison if you have Garmin dual sided power meter pedals. Has nobody done this comparison before? Did you check Youtube, blogs, etc, for anybody that has done this test?
Maybe one of these days I’ll throw on my Garmin Vector 3 pedals on my wife’s Peloton Bike and compare power between the Garmin and Peloton. I know my wife’s rides capture all sorts of metrics including a power graph over the entire ride as well as average and peak.
The problem is, they don’t actually have any ‘real’ power meter inside, but rather it’s just a function of cadence and the position (number) of the resistance knob. But the knob itself has no actual power measurement. The numbers on two different bikes, therefore, can be pretty wild, and testing one bike is really only meaningful for that one bike. When properly calibrated (big asterisks,) Peloton claims accurate to +/- 10%. Let that accuracy fall out (as they are very known to do), then welcome to 550W FTPs.
I’ve ridden one a good bit, and mine seemed accurate-ish. If anything, I’d probably say do the FTP test in their Power Zone class and just build your FTP based off of whatever if gives you. It’s not reliable enough to just punch in your existing FTP. It does seem relatively consistent, at least. The numbers while riding seem reasonable, if you exclude the crap power smoothing they implemented.
I have a set of Garmin Vector 3 on my Peloton. The Vectors are generally higher, but not in a linear manner. At very high cadence, the numbers diverge further with the Vector reading a full zone ahead of the Peloton. My most recent FTP test was 255w on the Vector and 223w on Peloton. I think the Peloton is VERY repeatable, so if you do only Peloton rides, your zones will be correct each time. However, it isn’t comparable to your outside rides. Strava will not let you have 2 different FTPs, so one of your rides will be misestimating your TSS depending on if you pick power meter or the Peloton numbers. I have stopped sending Peloton numbers to Strava and Trainingpeaks. I have 2 sets of Garmin Vector 3 to try to centralize around a single number whether I’m on the Peloton or my Road or Tri bikes.