Power Meter 40W-50W Higher than Virtual Power

Hey @klew!
You didn’t mention which trainer you’re using with VirtualPower, but I’m here to tell you that VP is just a rough approximation of your power, and one that is very easily affected by other factors like trainer and tire pressure, as well as the relative accuracy of the VP curve in question.

We answer this question under the “VirtualPower Watts vs. Power Meter Watts” section of the following article, and there is an explanation of the factors that affect VP above that:

Just to clear up any confusion, our best recommendation is to re-test your FTP with your new Stages power meter and continue training with your power meter. We always recommend a re-test when changing the method of power measurement, and you’ll likely want to train with the Stages on the trainer since you can also use it outdoors.
I hope this helps! Cheers! :smile:

1 Like

Hey everyone.

Thanks for all of the responses. They are greatly appreciated.

I am using a Kurt Kinetic, tyres are always at 100psi etc. etc.

I did end up figuring out my issue though. Embarrassed to say that when I first started zeroing the power meter I was still clipped in :man_facepalming:. Once I zero’d the PM without any pressure on the pedal/crank the PM now measure about 5-8W lower than VP.

My biggest concern with this thread was to determine whether or not the PM required factory recalibration or if the numbers I was seeing were to be expected.

Chalk this one up to experience.

5 Likes

Borrow a hub or pedal power meter from a friend for a day and test your Stages.

*or buy. My Garmin Vector 3 pedals cost me AU$1509. And I’m still fuming at the week or so lost trying to get a broken set working. They did replace them, and the new pair are good. Still fuming.

4 Likes

Sorry Shane. I hope that didn’t come across as me saying you post crap online. Quite the opposite really.
Although I reckon you would’ve let me know if I was directly questioning your integrity. ;).

Fair enough. I stand corrected and you do buy equipment like the rest of us muppets. It also sounds like you get stuffed around just like the rest of us as well.
It sucks that most of us can’t test against units known to be accurate. If a power meter can’t accurately measure power it’s not really good enough and it really gets up my nose. It’s totally ridiculous that a factory calibrated unit could be sold with a calibration issue.

Glad to hear you solved your problem Klew. It happens to the best of us.

You’re all good. And yep, the stuff around is real. Very real. And when the story isn’t pretty because of the stuff around, it results in being shitlisted pretty quickly. Thankfully there’s a lot of vendors in the sea to fish with. And when they make a good product, the data doesn’t lie.

And then you find out the vendors are all using the same distributor and you have to rely on them for warranty claims on accuracy.
As the song by L7 in Quentin Tarantino’s Natural Born Killers suggests, I’ve made their shitlist.
I’m tempted to buy a flash trainer and have it tested for accuracy. Then offer it for a small fee to sniff out the BS locally.

1 Like

I’ve sent in my fit files to Stages and they want me to send in my power meter for testing. FYI, I have a 2018 Kickr and a Stages 3.

Part2…

So I did my ramp test today with the new power meter as scheduled. The PM lately has been running 10-15W lower than the VR after calibration.

My pre-ramp test VR FTP was 242 and after today’s ramp test using the PM it now sits at 218.

Has anyone else seen such a drop in FTP when going from VR to PM???

Would you be here asking this question had your PM given you a higher FTP than your VR FTP?

Yes/maybe it sucks to see the number go down, but it is relative since going forward your training will be using your PM as the power source.

Lastly, I would trust the Stages over the virtual power. Be sure to zero offset it w/out your feet in the pedals before each session and you should be good to go.

Yes. I went from a FTP of 485W to 286W switching from VP to powermeter.

1 Like

I hear what you’re saying but yes, I would be here if the FTP number had as big an up swing as it did a low one.

Just trying to figure out if the PM is wonky or not. I haven’t had a chance to use it much at consistent levels but I am curious to see how it performs at “low, medium and high” watts over a significant amounts of time. Try to see if average watts and RPE match up after repeated workouts.

Thanks for the response.

AndyGajda, thanks for sharing.

I guess you can have an indoor FTP and an outdoor one.

How did you (or anyone else reading this) go about testing their outdoor power? Best 20mins from a group ride, actual field test, a ramp test or a guess?

I think you’ll be fine. My buddies who use Stages are happy w/their purchases.

1 Like

We need to put this as a banner on the top of this website:

VIRTUAL POWER IS NOT A MEASURE (OR EVEN AN ESTIMATE) OF YOUR ACTUAL POWER OUTPUT.

4 Likes

Yup, bold… double underlined… and flashing… like a 90’s web page.

It’s “virtual” for a reason. I almost wish they had made a unique name for the data from it. “Power” and “Watts” in use imply far more than what we commonly see with these setups.

It leads to the “I lost power when I got a real power meter…” comments. No, you didn’t lose anything. You just changed the tape measure that you were using.

Effectively you moved from a sloppy photo copy of a ruler (with scaling issues), and you got a digital caliper with real precision and accuracy. Virtual power is the sloppy copy, and the power meter is the digital caliper.

Yes, some virtual power setups can correlate well to real power measurement. But based on the many posts like this, I expect it is the exception rather than the rule.

2 Likes

Yeah, OK. Thanks for that.

I understand that there will be a difference between a PM and VR but what I was trying to figure out is how much of difference is “normal”. I assumed PM’s will different from model to model and from model-unit to model-unit but in the end what I was really after was whether or not big swings are the norm. It seems like they are so I got what I was looking for. Thanks to all who responded.

1 Like

The last ramp test I did on a Kurt Kinetic with virtual power gave me an FTP of 324. Then I got a stages crank and retested 2 days in a row. First one came in at 298 and the second was 296. Pretty massive change from the virtual 324. I’m definitely fitter and faster now, 5 months later, than I was then. Though I think my VO2 has suffered with all the sweet spot work.
I ran virtual and stages side by side and the numbers were close when I was doing an endurance workout like Petit but the numbers were way off once I got above threshold. The virtual power was estimating a much higher power output.

1 Like

Exactly same with my kinetic road machine (with Virtual power) and my 4iiii. At lower power levels they tracked pretty well upto (if I remember correctly) around sweetspot (about 250w) for me…but as power went higher then VP started to get higher and higher and higher…I used to think I rocked at v02 work…I do not! Lol. Power meter so much better.

2 Likes

This is the best post ever on the TrainerRoad forum!!

1 Like