Virtual power readings jumpy + changing cadence/gears

Virtual Power
I just started using TR and noticed my power readings are extremely jumpy and inconsistent. Below is my set up and a screenshot of my workout. In the screenshot, you can see it was nearly impossible for me to hold the same power output. Additionally, at each sprint interval, it would take a few seconds to ramp up to the target power level (at which point I’d go way over due to lag) and similarly, it would take a few seconds to bring the power down after each sprint. I’m not sure if it’s user error, improper setup/settings, or just the inherent inconvenience of relying on virtual power. Any thoughts?

My set up: bike on TravelTrac Comp Fluid ‘dumb trainer’, set at my tire circumference (700x35 = 2168mm), Wahoo RPM speed sensor, Garmin Cadence sensor.

Changing cadence/gears
Pardon my ignorance, but should I be shifting gears while on my bike throughout a workout to reach the target power outputs? Or is the goal to stay in the same gear the entire time and change my cadence? Is there a right/wrong way in this regard to optimize results?

Outside of the work intervals, that doesn’t look “jumpy” to me? A bit of fluctuation is completely normal. (If you see a perfectly flat line, its because it’s been smoothed).

The lag before/after the work intervals is likely due to the way virtual power is calculated. It needs to measure your wheel speed, which probably needs a few rotations of the wheel. I wouldn’t stress about it, just hold the interval power for as long as the workout says, and don’t worry too much if the graphs match.

Regarding shifting - yes absolutely, on a “dumb” trainer with virtual power, you’ll have to shift, same as you would on the road. The “no need to shift” is only for smart trainers in erg mode (and even then it depends on the trainer).

As you’re using a wheel-on trainer with virtual power, make extra sure that your trainer setup is identical between workouts - exactly the same tyre pressure and contact tension between the tyre and the trainer. Otherwise your resistance/ppwer will vary a lot. Also virtual power is a very rough estimate, so don’t compare your power numbers with others who have power meters.

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virtual power is based on wheel speed, wheel speed is 100% dependant on cadence and gear ratio. So you should 100% be shifting gear, to “the right gear” to get to a target power.
My experience with virtual power was that it wasn’t jumpy at all, because is would just hold my target power based on a steady cadence. Keep cadence steady = steady speed = steady power.
However, on a later update of the app, i did notice the virtual power would jump up/down in increments of 9 Watts. Where before it was maybe 3 Watts. That does make it more difficult to be more precise with the right power. And sometimes impossible to get it exactly on target. For example:
target 300 Watt. Virtual power says 295 Watt, so you increase cadence a bit, then it says 304 Watt. So you decrease cadence a bit, it reads 295 Watt again. It is Watt it is :wink:
On shorter, higher power intervals, you will need a few intervals to get a rough idea which gear and cadence gets you to target power. So maybe go a little easier the first interval and hold it a little longer to see where virtual power is at compared to target and adjust it for the next intervals.

Further experience with virtual power. Yes it takes maybe 5-10 seconds for power climb up and down. its a matter of the wheel speed increasing, the sensor picking that up, sending it, in 1 second intervals, to the app, the TR app translating speed to power. And decreasing you have the flywheel making it lag a bit. Dont worry, just try to to the workout as intended. If the graphs dont 100% match, whatever, it matters your body gets the intended workout. With time you will get better at knowing which gear and cadence is right for which (virtual) power.

I was able, eventually, to have near flat power lines, because i would just hold my cadence very constant and therefore, virtual power (looking) very flat.

Shifting may or may not be required, based on the power difference between recovery and work levels, the gear you have and preferred cadence. However, in recovery power, its a good idea to spin light and quick and not grind. For me, i often used the front chainring to go from recovery to work levels.



On the dumb wheel-on trainer I’d use the warm up intervals to figure out my gearing. Usually you find that a simple switch from small to big ring at the front and back again is more than sufficient with possibly a slight cadence change.