How stable should my power reading be?

Just recently upgraded to a Smart trainer (WAHOO KICKR SNAP) from a year of using a ‘dumb’ trainer.

I’ concerned at the level of power fluctuation I’m experiencing and am being assisted by the technical people at WAHOO to resolve this.

This got me to wondering … what does a stable power reading ‘look like’ to other users… mine changes every second or so… by a minimum of 10 watts on a good day … it’s certainly in no way possible for me to hold a set wattage… no matter how careful I am… even with the 3 second average checkbox ticked.

I wondered, am I expecting too much in terms of stability?  Is this the norm?


I would depend on how efficient your peddling is and what your cadence is (lower cadence might have more fluctuations). I use a power meter and can hold my watts with a 5 watt range for a prolonged period of time.

With any powermeter is quite hard to hold the power. Even with the 3 sec average. It’s quite normal IMHO. 

Looks real Zwifters and even keeping speed and cadence, the watts are not so constant.

Derek, I own a Kickr Snap and experience the exact same thing as you.  I only do workouts in ERG mode because the power jumps around too much and the game constantly tells me to increase or decrease wattage in regular mode during a workout when on 1 second power.  3 seconds power smoothing helps with this.  I believe this is normal.

Trainers with a power meter or actual power meters will always fluctuate more than a speed & cadence sensor setup.

Hi Dylan, thanks for this. Wahoo support came back to me yesterday after analysing some files I sent them.

They asked me to return the snap as the optical sensor was faulty.

If the replacement device is as poor I’ll need to consider another trainer.

Group rides in Zwift are not possible with the current issue. Constant fluctuations of +!- 60 watts are not on.

I’ll report back of this resolved the issue.

(Forgive any crazy typos… On the express… No seats)

Sounds like your problem was more severe than I thought.  Good to know that Wahoo is taking care of you.

Cheers Dylan… Wahoo technical support have been excellent. Super responsive. The fact that the UK hours of service are 3pm - midnight UK time helps too!