Watts vary significantly even on flat route

Curious if anyone else has same results, I can be on a Zwift ride on my Kickr direct drive and my watts will vary 10-20 one second it is 120 then goes to 140 then to 130, etc watts up and down with me keeping same cadence and speed. Not sure it’s an issue w trainer or Zwift, would think I could hold a fairly steady watt output on a flat road, Thanks

Hi @Jeff_Gaster

Welcome to the forum.

The image you posted is your PC Frames per second not watts, am I missing something?

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Hi @Jeff_Gaster, do you have your settings in Zwift at instant power or 3 second average power? This is a display option only, it doesn’t effect your actual power output, but it can help “smooth” out the displayed power on the screen.

@Mike_Rowe_PBR HI, I have 3 second average, should I switch to Instant?

Here is the ride

I would leave it at 3 sec avg

Thanks @Mike_Rowe_PBR Here is the ride profile with watts

I wouldn’t spend too much time worrying about it, there is always going to be some variation in your power, even shifting your weight in the saddle or sitting upright will cause it to change.

When in ERG mode, it should hold a constant power regardless of your cadence. If you are seeing variation in ERG mode (doing a workout), then I would be concerned.

Thanks Mike, appreciate it.

One issue is it depends on what power meter you use. If you use a crank-based power meter, that measures power over each pedalstroke. If you use a hub-based power meter (including many smart trainers), power is typically measured over 1 second. But power varies over each pedalstroke, so if you have a cadence of 60 or 90 or 120, no problem, you get an even number of pedalstrokes, but if it’s not an even number of half-pedal-strokes, then you might get a different number of “power strokes” one second to the next. Averaging over 3 seconds helps with this but won’t eliminate it, especially at relatively low cadence.

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That’s the problem I have. Some workouts hold me at steady power and the next day it’s like ERG mode is off even tho the companion app says it’s on and the radio button is checked when I select the workout.