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I have the exact same experience as the OP. I use a Stages II power meter transmitting to a Garmin Edge 520 while I also use the Virtual Power available in Trainerroad for a KK Roadmachine. I find that due to electromagnetic interference in my basement with a ton of WiFi and Bluetooth flying around, I get too many dropouts to rely on the Stages/Garmin for my indoor training sessions. Therefore, I use virtual power exclusively for my training baselines/FTP etc.
I can report that at power above around 150W, the power reported by Stages begins to lag considerably behind what trainer road is reporting. Below 150W, the stages mat report higher power. As I approach 300W, this divergence increases anywhere from 25-50W. Recognizing that Stages is left leg only, I gave consideration to left-right asymmetries, but I can conclude after enough experimentation, that the reported divergence is not a physiological artifact but a misalignment in the virtual power curve relative to what my Stages is actually measuring. As stated above, what is most important is that you decide on one method, and stick to it while in a training program. For this reason, I am more than happy with the virtual power method even if it is not accurate in absolute terms - it is simple and robust. Just don't expect to be able to compare FTPs with your friends. Or if you do, be careful about bragging because you may find your FTP is over-estimated by trainer road by a substantial margin. |
Originally Posted by SkepticalOne
(Post 18876843)
Recognizing that Stages is left leg only, I gave consideration to left-right asymmetries, but I can conclude after enough experimentation, that the reported divergence is not a physiological artifact but a misalignment in the virtual power curve relative to what my Stages is actually measuring.
The dropout thing when indoors does get annoying. I wish they came up with a way to avoid interference issues. |
Originally Posted by PepeM
(Post 18876895)
I figured that would be pretty easy to test (just pedal with one leg and compare) but since the OP didn't seem to come back I didn't bother posting.
The dropout thing when indoors does get annoying. I wish they came up with a way to avoid interference issues. |
Originally Posted by TMonk
(Post 18874585)
Also, I could have been more graceful with what I was trying to communicate here:
Many cyclists in competitive circles, like rev. and myself, use the term "over training" somewhat loosely. True overtraining is quite rare and does have some physiological significance, I agree. If one tends to overreach for a few rides, say, a couple weeks' worth, when you're already fatigued in the first place, it can take a while to recover out of that TSB hole and actually be counter-productive to your long term fitness. Really it's just "fatigue", but we like to refer to it as "over training", potentially because the term has some clinical and prescriptive connotation to it. Many of the symptoms of true over training like chronic injury, illness, irritability can start to rear their ugly heads in this medium-term time view. This is why we have felt that you are being so pedantic - because we chose to misuse the term :). http://www.ncbi.nlm.nih.gov/pmc/arti...8111434406.pdf |
Originally Posted by RChung
(Post 18869139)
Which trainer?
I feel your pain. People buy power meters to resolve uncertainty, not to increase uncertainty. Many people are convinced that accuracy and the ability to check it is unimportant -- they're convinced that consistency is all that matters. Here's a case where your Stages appears to be consistently lower than your trainer but you don't know which is right, which is causing you more uncertainty about your training. Many (but not all) power meters allow you to check their accuracy fairly easily. Sadly, the Stages isn't one of them, so you don't know whether the problem is you, your trainer, or your Stages. There are ways to check the Stages but they're considerably more trouble -- or they require a calibration rig or another power meter that is known to be accurate. Fans of the Stages often point to Team Sky and say if it's good enough for Sky it's good enough for them. Team Sky has enough other equipment to check their Stages. Most people don't. If you really want to know, you'll have to find someone with a known accurate power meter who is willing to help you determine whether it's the Stages or your trainer. If both are okay, then it's you: you have a huge left-right discrepancy. |
Here is the latest…
Yesterday I performed a threshold test on my indoor trainer (rollers, actually). While doing so, I recorded the pertinent data from my Stages power meter on my Garmin Edge bicycle computer. I used TrainerRoad's VirtualPower feature as a second data generator/recorder. It was the power data estimated by TrainerRoad that I used to calculate my FTP. When I finished, TrainerRoad calculated my FTP at 255! My previous threshold test, using data from my Stages power meter, resulted in an FTP of 145. That's quite a discrepancy! My guess is that the truth lies somewhere in between. For what it's worth, I have attached a Garmin FIT file generated during that session, which contains power data from the Stages power meter. For comparison, I've included the TCX file from that same session, containing virtual power data from TrainerRoad. |
What rollers are you using?
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Hmm. I thought I could upload a file, but I don't see any evidence that happened.
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Originally Posted by PepeM
(Post 18878159)
What rollers are you using?
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Originally Posted by babyboomer
(Post 18878168)
InsideRide's e-motion rollers
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Also, have you played with their power calculator? It shows how big of a difference variables such as weight can make. I don't know what power curve TrainerRoad uses, but playing with the calculator I can see that in Level 1 resistance, 15mph would equal about 157 watts for a 150lb rider but 192 watts for a 200lb rider. Unless TrainerRoad is asking for your weight and varying the power curve accordingly, there is big room for uncertainty there.
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Originally Posted by PepeM
(Post 18878194)
Also, have you played with their power calculator? It shows how big of a difference variables such as weight can make. I don't know what power curve TrainerRoad uses, but playing with the calculator I can see that in Level 1 resistance, 15mph would equal about 157 watts for a 150lb rider but 192 watts for a 200lb rider. Unless TrainerRoad is asking for your weight and varying the power curve accordingly, there is big room for uncertainty there.
I have downloaded Inside Ride's Excel spreadsheet tool. That tool allows you to change the weight. I fiddled with the numbers to see how closely they approximated those generated during the threshold test. They seemed to correlate with the numbers generated by the power curve used by TrainerRoad. |
I'm assuming that 180 is rider's weight, which is pretty close to your weight then. Do you calibrate the power meter on your Garmin before using it?
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What happens when you ride outside? Can you sustain, say, 200 watts per your Stages or does it feel super tough?
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Originally Posted by Heathpack
(Post 18877651)
Interesting food for thought: what are the definitions of these terms?
http://www.ncbi.nlm.nih.gov/pmc/arti...8111434406.pdf |
Update…
To their credit, Stages has agreed to replace my power meter. I'm not likely to have the new one for another few days. Once it's installed, I'll give it a spin and publish the results. Either my suspicions will be confirmed, or I'll have egg on my face. |
FWIW I just built up my new bike with Power2Max meter on it. Two rides on the Kickr and it tracks pretty much spot on with the Kickr power readings.
In emails with the Stages support so will see what their thoughts on this are. |
My experience with stages wasn't good either. At one point I did have 3 different powermeter handy... Stages, Quarq, PowerTap... actually another one was indoor trainer... (direct drive one with FE-C).
Tracking few times for various test... one that always was further out then rest... would be Stages. If it was persistently off by some offset scale, I wouldn't have worried about it. But... it was some what random and I couldn't find pattern... Sometimes off by as much as 10%. Over the course of 1 hour ride, difference would be only 2-3%. But intervals, etc was hard to count on and I gave up. Maybe there are some Q/C issues. I did return mine and never looked back. |
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