I like to ride in Zwift while doing my TR workouts. Today I tried an experiment: I connected my left-side crank power meter (4iii Precision) to Zwift and used my Elite Suito smart trainer power meter for TR. I was surprised to see that the 4iii power meter was consistently 10-15 watts higher.
I then set up TR to run using the Powermatch feature and while the difference was less, the workout was much easier than when I was doing it with just the Suito power meter. For what it is worth, I was in ERG mode.
Any idea which is more accurate, and which I should be using?
Also, sorry if there are already threads discussing this exact issue but I couldn’t find any recent ones and I think TR recently upgraded their Powermatch feature.
PS: yes, I calibrated both power meters before the workout.
Not a chance we can answer that without at least a 3rd power meter in the mix.
Depends on your goals. If you are using the power meter for outside rides and races, using that same “tape measure” via the PowerMatch feature is best. This makes sure you use the same device in all your use cases.
PowerMatch changed, but it was well over a year ago IIRC. Regardless of the improvements made, it does not significantly change the core issue here… power devices often report different data.
Keep in mind, if all you are doing is “eye balling” the delta by quickly looking between two screens, this is far from conclusive. It is impacted by the smoothing setting in place in each app at the very least. Even if those are “matched”, the sampling and data presentation between them is not guaranteed to be “comparable”.
If you really want to head down the comparison rabbit hole, you need to take more steps.
With respect to the feeling you have, that is a direct result of changing from “tape measure 1” to “tape measure 2” within TR. You effectively shifted the data point that sets the resistance, and as such, will alter your experience. It’s totally expected based on the apparent delta from your rough comparison.
Thanks for the reply. Yes, I do race and use power outside, so maybe I will stay with Powermatch. I am just surprised by how much easier it was. I have always felt I could hit higher power numbers outside, although I know there are other factors for that as well.
Firstly, because of drivetrain losses, and the 4iiii measuring “upstream” in the drivetrain, you can expect it to read slightly (1-2%) higher than the Suito, even if both are 100% accurate.
Secondly, potential L/R imbalances in your power output mean the 4iiii (which doubles the left leg) may not be reporting the same as the Suito (total output) , again with both PM’s measuring 100% accurate. Power imbalances are the more likely cause of the difference in reported power.
If you are doing a mix of inside and outside workouts, you may want to use powermatch for consistency,
But if all your structured rides are inside, and outside rides are just free rides, then you may want to use the Suito as your power source.
That’s a good point. I race and ride outside with power, but I do not train outside. I strictly train inside. So maybe I am better off sticking with the Suito. And I don’t worry too much about power during my races. I just ride hard and then admire the data after the race. I don’t use power data during the race to inform my strategy.
Then keep PowerMatch in place with both your power meter and smart trainer connected in TR and move forward.
One key note though, in a case like this where you are effectively switching between device A and B for power data, you should consider how and when you got the data for your current FTP. If you tested and got results based upon the trainer, and then swap to data from a power meter (that is different more often than not), your training may well be “shifted” one way or the other.
As such, the prevailing recommendation is to redo your FTP test anytime you make a notable change in power data measurement and/or trainer device.
Not much chance your left and right legs are putting out an equal amount of force. In my case my right leg usually puts out 2% more, so I’d be shafting myself out of some watts with a left sided power meter. I’d stick with the trainer.
IMHO there are no downsides to using PowerMatch. If you have 1 bike, it means you have 1 power meter and simplifies any analysis or estimates for pacing outside efforts. All upside, no downside.
Ditto. I get the notable aspect that the pedals are single-sided, but if that is used when reviewing outside rides (workouts or not), it makes the most sense to use the same tape measure in all cases.
Introducing an X-factor of a different device (smart trainer), just because it is “better” in the light of providing real, total power… is not enough justification to include what is already seen as a delta in the data. To a degree it might boil down to:
Is “total power data” with a delta used part time better than “1/2 power data doubled” the same all the time?
Both are “flawed” in essence, so I’d chose the one that is a consistent flaw inside & outside.
Yesterday i just for fun connected my brand new PM Magene PES P505 110BCD to Garmin 820 and on the other side started TR with training on Tacx Flux S smart trainer.
When paddeling on TR with Tacx i got almost steady 300w of power, on the other side on Garmin i got powers bouncing from 250-260w.
Why such a differences between these two? Btw both of them were calibrated before starting…
The fluctuation is likely down to power smoothing I suspect that the Garmin may be set to instant power reading or have a smoothing average (eg 3s ave) lower than TR.
The wattage difference is perhaps interference or a setup difference (stab in the dark the crank length factor). I’d suggest contacting support@trainerroad.com to see if they can get to the bottom of it.
Edit: at the end of the day there’ll probably still be a discrepancy between a pm and trainer for the reasons listed above. As long as the discrepancy is constant, its nothing to worry about, just pick one as the source of truth and ignore the other rather than diving down the rabbit hole!
As commented in this and several other threads, the TR Powermatch is the way to go if you have both a smart trainer and a bike equipped with a power meter. IMO you should always use the same power figures for TR and outdoor rides, provided by the power meter of your bike.
I just got a 4iii left side PM for my XC bike which I only ride outside and will not be using on my trainer. The hope was to be able to get more accurate data to TR for my outside unstructured rides. I havent used it yet, but now im concerned that this will negatively impact TR’s algorithm if I’m 10-20 watts above the norm while outside vs on my Hammer 3. Is there a way to better align these numbers? Any options that will make this useful?
Some power meters let you adjust the offset if its a significant difference, but remember with natural air cooling, momentum etc its quite normal that power outside is higher than in side. How it affect the algorithms I dont’ specifically know but I would expect TR have anticipated what is quite normal.
