Discrepency between indoor and outdoor power meter - what next

So here’s the rub.

I started in January indoor training, all ok, but as the weather improves I moved outdoors with unstructured rides, just having fun. Using AI ftp my FTP increased between 2-3% a month. As the weather has gotten worse i’ve moved back to indoor rides.

Doing a sweet spot today I was on my arse and had to lower it by 5%, I turned on my elemnt bolt and just for the sake of it to see if the power was matched my crank power meter, my crank was reporting 30 watts more than my indoor trainer.

So now i’m thinking my outdoor rides have looked more powerful than they are hence the increase in AI FTP over the summer and why i’m now struggling with sweet spot, threshold I just wanna die.

Any ideas what I should do next or shall I just put up with it.

My thoughts are:

  • Turn on power matching and do another ramp test - to essentially reset.

  • Just put up with it.

  • Do another ramp test based on indoor power.

  • Can trainer road analyse my last 10 ride and reset me…as they do when someone first starts out on TR.

Hey @James_Sanderson,

This type of issue is, unfortunately, not too uncommon. Most power meters and smart trainers have accuracy claims of around +/- 2% or so which can amount to an overall discrepancy of around 4 or 5% between two sensors (though there have been studies that have shown much greater gaps between some).

For context, when riding at 230 watts, similar to what you were doing during your Sweet Spot workout this morning, that equates to 11 watts.

Thirty watts is a pretty big difference. What type of power meter and trainer are you using? Can you confirm that you’re following the manufacturer’s recommendations for the calibration process and frequency?

It’s also worth noting that some devices read power data slightly differently (for whatever reason), and using one device to capture your trainer’s data and another (ELEMNT Bolt in your case) to capture your power meter’s data could, on its own create a further divide between the two.

The best thing to do in this scenario is to first ensure that you’re calibrating the two devices properly and as frequently as the manufacturers recommend, and then use our PowerMatch feature to close whatever gap there is left over between the two sensors.

There is likely to be a slight difference in how your current workouts feel once you’ve enabled PowerMatch, and we can’t “reset you” per se to account for a different sensor being used. The best option here would be to either retest as you mentioned or, if you can get through the workouts without too much trouble, Adaptive Training and AI FTP Detection should straighten things out as you move forward.

Let me know how it goes and if you have any other questions about any of this.

Best of luck!


I ran into the same issue (except that my trainer showed a slightly higher value than my power meter pedals). In order to have clean data and be able to compare indoor and outdoor rides I started moving power pedals between bikes and started using power matching.

Unfortunately, I had to reduce my FTP by 2%, but in the end it is much easier when you can compare the numbers between bikes and rides.

TrainerRoad will actually record which power meter you used so you can inspect that later. It could be nice to add an annotation in your calendar when you did the switch.

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The smart trainer is an elite zumo. It was fairly cheap at the time for smart trainer, the left hand crank pm is a 4iiii. I’ll try calibration on both tomorrow and try for 10 minutes to see if they match closer.

Thanks for your response.

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Outdoors in theory is easier for power delivery due to air cooling and momentum (although your physical ability to deliver an FTP is just one value given like for like), then you have + and - errors; which if the Zumo say under reads by 2% and the 4iiis over reads by 2% can be quite big; and another complication to throw into the mix is L/R balance on a single sided powermeter that could magnify the difference again. My approach would be to enable powermatch, make your indoor environment as cool as possible, continue to adjust the intensity down if you still feel the need and let the system (AI FTP and AT) adapt.