VirtualPower™ turns a indoor cycling trainer into a power meter. It uses an ANT+ speed sensor. As the user starts to ride, the speed will be converted to power based on the known power curve for the trainer.

https://www.trainerroad.com/virtual-power

Personally, I'd save the money, and just print out the power curve for the Kurt Kinetic and do my own math.

The power curve, and thus the Virtual Power are going to be reasonably accurate for sustained efforts,although tire inflation, how tight you have the unit cranked down, variance in a particular trainer will likely cause it to vary a bit.

Power for short hard efforts are likey to be pretty far off, given that I don't think the power curve necessarily takes into account the effort to accelerate to a speed. (i.e. spinning up to 20mph from 10 mph in 10 seconds is going to take a lot more power than maintaining 20mph).

So your not using it and never have, right?

correct. But I use a Kurt Kinetic, and have used it with 2 different power meters, a Quarq, and a power tap, and I've made my own power curve to compare to the published power curve.

My comments on the accuracy of a device that is based on the power curve are based on that experience.

It could be used for things like steady state intervals, if you know your FTP. However, for no money, you can set your power zone for the interval, just by hitting the speed that corresponds to the watts on the chart, without the need for the device.

i was thinking about using it til end of summer. I'm riding trainer a good bit right now, b/c heat outside i can't get the workout i want outdoors. If nothing else looks like it would be a good motivator while on the trainer w/ all the workouts. You can also watch something else while data is at bottom of screen. I doubt the power is very accurate, but if it's somewhat consistent that would be helpful. If it sucks i'm only out $10.

I think it would be kool if they would try to calculate power based on both the speed and acceleration of the bike trainer. I think you'd probably get a more accurate number, especially for intervals...

I did a few months of TrainerRoad last winter and was impressed. Granted, I've never trained with power before, but doing the various sufferfest videos with defined goals for speed/cadence/vPower seemed to make a much bigger difference than the year before (where'd I'd do the same sufferfest videos with RPE only).

Like a few others have said, it's only $10/month - that's a helluva lot cheaper than a dedicated PM (at least for the first several years)

Considering giving this a try for next season. I already have most of the needed hardware for virtual power. My one request was that sessions could be exported to a format Training Peaks could use, and it looks like they've taken care of that. See you in November : )

I used "virtual power" (non-™) about 2 years ago using my ANT+ sensor and my own software, and then went on to buy a powertap. The numbers are close, but for hard short intervals virtual power isn't very useful. For anything a minute or longer, you're good to go.

Some shots of it from 2010 using "virtual power" aka just calculating using the standard equation everybody uses:





If somebody wanted to get really fancy they'd take the first derivative of speed and apply some modifier to base calculated power. I don't beleive anybody does that yet, altho I've played with it a bit here. Haven't had time to finish.

For instance, if you sped up from 10mph to 20mph in 10 seconds, the normal equations would simply convert speed to power, so it'd show you going from 120w to 220w (or whatever). However, if you really did that in 10 seconds, you would have been putting out probably 400-500 watts until your speed was a steady 20, then it'd go back to 220w to maintain speed. Without those power spikes, you'll never get an accurate TSS or any guesses at sprint numbers.