Inconsistent Power

Hi All

I have a Stages left crank power meter on my bike. I use a Watt Bike at the gym (when it’s open) and a Saris H3 smart turbo trainer at home.

On the Watt Bike the TR Ramp Test gave me an FTP of 256w, on the Saris I get an FTP of 218w on the same Ramp Test and when I cycle outside I am holding powers of 352w for nearly 8 minutes (which I wouldn’t get anywhere near on the Watt Bike).

So basically I appear to have 3 completely different powers and FTPs. I would understand a small difference but these are huge.

All devices have been calibrated multiple times and all state that they are within a few percent of being accurate.
I wouldn’t mind so much but I would like to use TR for indoor and outdoor training but this isn’t possible. Indoors I would really struggle and score an RPE of 8-9/10 and outdoors I would sail through the same workout with an RPE of around 4/10.
Also, I can’t record an outdoor segment and then set the smart trainer up to train me for that section…so frustrating.

Anyone have any ideas why these three appear to be so far out? Power is power so I assume it must be to do with calibration but all are calibrated, all have the latest firmware and the chains are looked after etc. Yes there is a difference in temperature between indoor and outdoor training but not alter my ability to this extent.

I’m tempted to give up on power and just train by heart rate (which I know has its own weaknesses) but what else can I do?

Thanks for any ideas in advance.


First thing would be to put the bike with the powermeter on the trainer and see what that gives you.


Have you installed the bike with the power meter on the H3? Run that with two devices and watch power through a range, and at least this would give you a better window into the differences between the two. This offers no help for the Wattbike.

Sounds like you’ve evaluated FTP on each one, so you have a ballpark idea of the differences between the devices, at least around your FTP. Sadly, there is no simple answer (since you have calibrated). The reality of life now is that this is the norm, not the exceptions.

If possible, using what you already know about the differences, I’d try to pick my workouts and apply to devices as appropriate, for consistency. Meaning do your Threshold workouts on the same device, Endurance on another and so on. Try to keep at least some level of control instead of randomly matching workouts and devices. Not great, but there is not much better to off, AFAIK.

If you “ditch power” (which I don’t know is best) I’d suggest RPE as the replacement, not HR. Hopefully you’ve learned what RPE is for a range of workouts, and apply that in workouts regardless of device. It’s not perfect either, but slightly better than HR in ways.

I thought that TR had a feature to take the power from the Stages while controlling your smart trainer? If so, I’d do that and pretty much forget the Watt bike at the gym.

As suggested above get the trainer and the Stages going at the same time, warm both up for 10 minutes, calibrate, and then see how they match up at various wattages. Do that just so you know…

Beyond that you could do separate indoor and outdoor FTP tests on the Stages to see if you have much of a difference. On my Stages I really need it to be outside for 10 minutes before calibration otherwise it can read low. I’m not confident in it’s automatic temperature calibration.

Good point. I will have to learn how to take my rear cassette off and put it on the trainer but it sounds a sensible plan. Thank you :slight_smile:

  • Yes, PowerMatch.
  • But that presumes he is using (sometimes or always) the same bike with the power meter on the trainer. Many people use a different bike (one without a separate PM) on the trainer and keep the PM bike for outside only.

Never considered calibrating it into the ride even though I do that with the Saris when cycling indoors.
Will give that a go and see if that changes anything. Thank you :slight_smile:

Hi Chad

Good idea, I will give this a go sometime. Pretty sensible suggestion and I should have thought of it earlier. I recently got a Di2 geared bike and am terrible at bike mechanics so a little hesitant to fiddle too much but worth giving it a go as the imbalance between the indoors and outdoors is really frustrating.

Thanks mate

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I have two different bikes…one expensive one for outside and a cheaper one for indoors

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Not quite sure why you’d need to do that. What’s the setup of the bike on the trainer, and the one of your road bike? And also - what crankset do you have on both (it may be faster to move the crank in some cases).