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Smart Trainer - Accuracy and Calibration

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Smart Trainer - Accuracy and Calibration

Old 05-12-20, 01:18 AM
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ft_critical
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Smart Trainer - Accuracy and Calibration

Hi All,

Looking to get peoples experience on how accurate their smart trainers are for power?

My experience, which is in progress, is that I calibrated my Elite Direto recently (owned for ~2yrs and used a lot) and it was 8pts off. So I tightened the band per instructions (having taken it apart and sent pictures of it to Elite in Italy). When calibrated using the Elite App, it is nearly impossible to ride on Zwift. This seems to be a 'known' issue if you read the Elite forums. I have a second hand set of P1 Powertap pedals arriving this week so I can do an 'external calibration' and I will post an update later. I tried to undo my change to get it back to how it was originally, but that hasn't been fully possible though it is largely ride'able again.
I am left in the situation of not knowing what my actual power, therefore performance is, on Zwift for example. Comparing to the days I had a road power meter, my Zwift results seem a little higher pre-calibration but lower now that I have tried to revert.

This has me wondering about the performance accuracy of all these people on Zwift on smart-trainers (and other platforms, RGT, Rouvy, BeKool etc). Hence my question - have other smart-trainer users experienced that they are inaccurate if not calibrated or potentially even when calibrated - Wahoo, Tacx, Elite etc..?

Cheers,
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Old 05-12-20, 12:27 PM
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As an engineer, accuracy is something I think about. However, one has to ask the question, "What is the reference standard for power meter accuracy?" I.e., is the meter on your bike 100% accurate? Is the trainer meter 100% accurate? Are either accurate? Is there a gold-plated set of power-meter-equipped crank arms locked in a vault in a secret location in France that define the standard for accuracy that all other power meters are compared against?

I'm of the (unpopular) opinion that as long as the power meter's measurements are remotely close to everyone else's and consistent with it's own readings over time, that's all one can really hope for.

Sorry to not answer your question and probably just make you more confused
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Old 05-12-20, 12:59 PM
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I have a wahoo kick R, and last year put my road bike on it with a quark power meter, the watts displayed were pretty accurate , with in a few percent.
the power meter displaying on my wahoo element on the handle bars
I had to take the road bike off because the blue tooth connection between the quark and the wahoo sending signals to my I phone were really messing each other up
when communicating with the zwift app.
I was having to do a spin down with the wahoo every couple of days, and doing a spin down on the power meter to reset both of them just to ride a couple days
so now I have a dumb bike on the smart trainer and much better
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Old 05-12-20, 10:30 PM
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I use a Tacx Neo which does not need calibration, one of the Neo series' plus points.
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Old 05-13-20, 03:59 AM
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If you search DCRainmaker and/or GPLlama for smart bike power meter tests, you'll see they have done very solid comparisons of pretty much every smart bike out there against the power (often multiple) meters on their bikes. As you'd expect, some trainers are more accurate than others and in general wheel-off trainers (which cost more) are usually more accurate than wheel-on trainers. That's why some of the online racing rules require wheel-off trainers to be used.

It is one of those "you get what you pay for" and "you should pay for what you need to get" kind of things. Probably 90% of the riders on Zwift don't use power meters on their bikes in the real world, so any power numbers online are just for online purposes anyway.

I'm one of that 90%, been using Zwift for 4 years now but don't have a power meter on my road bike or my what is now called a gravel bike. I like doing races on Zwift as workouts, do structured workouts and lots of just plain exercise rides - and I like increasing my FTP on Zwift because it indicates my fitness is increasing. But the absolute value of my FTP on Zwift (based on my wheel-on Kickr SNAP trainer) is meaningless, since I'm not really competing in races.

When you look at all the others factors that aren't very accurate when you ride online (Zwift or any other), I'm not sure power meter accuracy really breaks into the top ten issues other than for pure online competitive racing!
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Old 05-19-20, 01:25 AM
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I managed to align my Elite Direto to my P1 pedals by adjusting the smart trainer band tension. This leaves it -7 from calibration using the software - somewhat alarmingly. The P1 pedal, based on testing, is above the SRM at higher cadences >90rpm by ~2% but considered very accurate.

Much as you have suggested above, it is a relative measure (to self), but not that reliable as a measure of peer performance. So the only known measure of performance remains in a race, on the road, in real life, I guess.
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