Stages /Trainer power accuracy

I’ve recently purchased a Stages power meter and although I’ve Zeroed it I’m getting big watts compared to my trainer power and this accelerates my tss value to bigger numbers.
I’ve got an example showing two almost identical rides with almost the same elevation with the fulgaz ride being indoors and the other outdoors.
The trainer was set to 80% difficulty for inclines which could have a bearing.
I am left leg dominant due to a football injury on my right leg and my power meter is left crank only.
Any advice would be welcome to the issues if any.

Can you use your powermeter when on the trainer as well?
I have a Quarq PM, that i can use both indoors and outdoors since my outdoor bike is the same i use indoors. Even when i’m indoors i use the readings from my PM instead of the readings from my Kickr. That way, i know for sure that my wattage is consistent both indoors and outdoors…
If this isn’t an option for you, i suggest you do a ride indoors and record both the PM and the trainer values. Then you can see what’s the average difference between the 2 of them. And then you can plan accordingly.
For example, if the trainer reads 20W lower, then you know that when you’re on the trainer, you need to push harder so you can match those 20W difference. Did this made any sense? Apologies if it’s kinda confusing. English isn’t my native language so sometimes my train of thought gets lost in translation…

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Just as @brunocfeijao says I use my powermeter power (Quarq) when I ride indoors and outdoors. Never the power from the Kickr. This just keeps the numbers consistent. My Kickr reads higher than my Quarq.

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Forgot to mention that I have a different bike on my direct drive Elite Direto trainer which is old and a nine speed.
My outdoor bike with the stages power meter is 11 speed and not compatible unless I change the sprocket to the trainer to match.
Is there any other way to test accuracy?
I’ve signed up to Fascats coaching subscription and my tss outdoors is higher than expected for the duration and I believe it’s not accurate outdoors.
Is it required to calibrate the stages meter before every ride and is it required to do this on my Wahoo edge or is it the same thing using the Stages App instead.

Well, with different bikes for indoor and outdoor, i don’t know how you can test for accuracy. So we are oficially in uncharted territories for me, so i’m afraid i can’t help you. Hopefully someone with some knowledge comes in and gives you a hand…
Best of luck mate.

Just remembered, maybe do an indoor FTP test, and an outdoor FTP test and train accordingly?
If doing indoor workouts, use the Indoor FTP, if doing outdoor workouts, use the outdoor FTP?
Maybe this is doable? Not sure if this a big no no from a training pov, so maybe one of the coaches can say if this is a good idea or not…

You should calibrate your powermeter before every ride. I know some newer ones you do not have to as it automatically adjusts but it is good practice I suppose.

You may need to have different training zones for indoors vs outdoors. Unfortunately TrainingPeaks does not make this easy. You will just have to adjust TSS accordingly if you want to track properly.

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that could be part of it. And you have total power inside (Elite Direto), and left-only power outside. Hard to say much else without looking at some power data. I’ve owned Stages gen2 left-only, and Stages gen3 dual-sided, and both are very close to the power on my 2017 Kickr (wheel off / direct-drive). However I always record Stages both inside and outside to have one source of truth.

Update on my Stages power meter.

I decided to fit my road bike to my trainer to compare power numbers with my Elite Direto trainer.
As suspected I had a 25% increase of power on Stages for example: Direto = 150 watts Stages = 200 watts.
I had a look at the Stages app on my iphone and noticed a setting called gyroscope that is used apparently to improve cadence on rough terrain such as mountain biking (uses 25% more battery though).
I turned this on and immediately saw a drop in my power similar to my trainer.
I’ve now disabled it again and still has similar results to what I expect and I have now contacted Stages support with my findings.

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Very interesting Marino (and frustrating I can imagine)!
Let us know what they tell you.

interesting discovery. I recently replaced a Stages Gen 2 as it seemed it was also over-estimating power compared to my Elite Direto X by ~10 watts. It seems much better now with the new model. I haven’t messed with the gyroscope setting just leave it off. Please do report back what Stages says.

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I’m still in communications with Stages support but I’ve found a useful free power comparison tool with if your registered.
It allows you to compare power outputs from different power meters from your rides (.fit files) etc. and it’s quite interesting if you are into that sort of thing.

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Hi @jamesstevens , I had a similar discrepancy with my power meter (pedal based) vs. trainer. After a lot of reading + playing around I came to the conclusion that a difference is to be expected as you’ll lose a material amount of power through your drive train (2 to 4% seems reasonable).

As I understand it, the power accuracy quoted for turbo trainers is accuracy at the point of measurement (so after drive train losses) so readings will differ to crank or pedal based power. As a result of these findings, to ensure consistency, I now use my bike based power meter as my main source for all rides, including when on turbo.

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I might have resolved the issue and think it was related with my Wahoo Element Bolt bike computer.
I will confirm it over the weekend and let you know.
My difference between the meters varied by +25% in the beginning and -10% towards the end (big margins).
Hopefully it will be about ± 2% now and that will do me just fine.

Your right @seanv there are a lot of variables to consider comparing between power meters and especially trainers and 2-4% is reasonable and can be worked with.
It was interesting comparing the power data though with the free analysis tool from zwiftpower.

@seanv thanks for the info. I too use my bike PM (Stages crank) for both indoor and outdoor rides for consistency,

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Hi Marino, I tried the link you gave. It takes me to a forum page that is now superseded by a new Zwift forum. I could not see the comparison tool on either.
Do have a have a more specific link please? that would be most appreciated as I am looking to review the differences between my pedal and trainer power.



This is how I did it Tony using a pc.
Search (Zwift log in) on google
Go to - log in (if already registered) or register- sign in - select profile - select tab analysis-
Create new data set.
On the page you can select a previous ride from zwift and compare with the power meter by adding a .fit file.
You can add 2 fit files if you didn’t use zwift to compare two different power meters.
The files need to be . Fit and unzipped.
When you add a fit file, give it an Id so when you compare you know what meter is attached to each data graph.
Hope it all makes sense and let me know how you get on or any questions.