Stages Power Meter Left Side Only

I just got a Stages Power Meter and have been using since about an year ago. Now this spring I am paying more attention to it and training by power consistently. It just seems like the power fluctuates unexplainably during intervals. I see two things. One it seems like the longer the interval the power goes down even though I am in in the same gear and cadence. It seems like when I increase my cadence sometimes the power goes down? Is that supposed to happen.

Yes, if you are in ERG mode anything you do cadence wise will affect the ERG and youll see a fluctuation in power. If you increase cadence that increases power, so the trainer will then dial back power to bring you back to target, and that usually involved a temporary dip below the target as well. That said, power is not flat or smooth, its always spiky, so as long as you’re hitting the interval targets don’t sweat it

I should add. I am on a dumb trainer. Cycleops Fluid 2.

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as the unit heats up it’s resistance will change.(the trainer, the PM has a mechanism in place to compensate for temp changes.)

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Yes, you’re experiencing a viscosity change as the unit and fluid unit heats up during longer intervals. That happens with some trainers, despite efforts to use fluids less impacted by heat. The CycleOps ones are known to have this issue.

You will need to adjust your cadence, gearing or a bit of both to keep at your desired power target.

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What @mcneese.chad said. I used to have a CycleOps Fluid 2 also and used it for years in with Virtual Power and always thought the intervals got progressively harder over the course of a workout. It wasn’t until I bought my first power meter that I realized it was in fact the resistance unit getting progressively harder throughout.

So does that mean even though the power is going down the longer the interval that outside the power would remain constant.

You can’t keep power nailed at 200W, 210W etc, it will fluctuate. Also worth ensuring you are looking at 3s power or even bigger.

Hmmm. I think I’d look at it from a slightly different point of view. Your Stages PM is reporting power consistently. It’s your CycleOps Fluid 2 that’s giving inconsistent resistance. So while it seems natural (like riding outside) that at a given gear and a given cadence that your power should remain constant… in this case because the resistance is changing over time the power at that gear/cadence will change, or the gear/cadence will have to change to keep steady power.

Knowing that, it will probably be better for hitting training power targets to just change cadence / gear as needed to maintain target power.

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Two things:

  1. The fluid becomes less viscous as it heats up (as others have mentioned above). This shouldn’t cause erratic power fluctuations though.

  2. It’s a Left only Stages. It’s doubling the left crank only so you’ll get erratic power as you shift position or do anything that effects your LR balance. Your balance can also change based on power output, cadence and how fatigued you are.
    It’s best not to worry about it too much and just keep the averages in the right zone.