Watts lost in frame?

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tiberiade
Posts: 61
Joined: Mon May 08, 2023 6:02 pm

by tiberiade

I recently returned a Neo Tacx and received a replacement from Garmin as I was experiencing significant discrepancy between the data of the trainer and my Quarq powermeter (Sram Red crank). After installing my carbon bike onto the new upgraded Neo 3M, I'm observing the same issue.

I own another trainer, a JetBlack Volt v2, which delivers similar data to the DuoShi I have on my second bike, a custom steel XCr frame. Essentially, the data from the JetBlack, the DuoShi and my Quarq all seem to match up. The only powermeter delivering vastly different numbers is the one from the Neo. We're talking 10-12w at 200w and 250w at 1,000w — a wild difference.

Transmissions are a bit different — 1x Red XPLR on the carbon frame, 2x Campagnolo SuperRecord on the steel frame. Both with waxed chains.

Could I be losing a large amount of power into my carbon frame? Could I have received another dysfunctioning trainer?

While it's not the end of the world, it's a little weird to be training at 300w FTP on one setup and 270 on the other. Any ideas what the issue might be?

usr
Posts: 1023
Joined: Thu Mar 25, 2021 5:58 pm

by usr

10% would be a lot of deflection. 10% more pedal travel...

All your bike PM are measuring before chain losses are applied and if the Jetblack is spot on with pedal or crank it's off by whatever is lost in the transmission. Which might actually be a deliberate calibration tweak because yes of course, users prefer the numbers you be consistent with their other sensors. Not saying that your transmission eats 10%, but a meaningful part of those 10% and the rest of the difference is really not that big.

I'd just do my inside training to the sensor I also use outside and be done with it. What I did use my Neo for is calibrating pedal PM (bepro and assioma) against each other: recorded both for a while, then copied the pairs (pedal and Neo) of "best 20 minutes" numbers into a spreadsheet for each pedal to get each pedal's average factor to the shared base (neo) and then configured the Bepro with the a factor to get roughly the same difference as my Assioma. I don't even remember what direction the Neo was off. What I do remember is that even within the same pedal/neo pairing the "best 20 minutes" ratio varied quite a bit from session to session. PM data is noisy. Just look at the details part in any DCR review: zoomed in, the numbers are all over the place, but Ray praises them nonetheless because he knows how bad they used to be (while still good enough to revolutionize training)

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tiberiade
Posts: 61
Joined: Mon May 08, 2023 6:02 pm

by tiberiade

Thanks, this is very useful! I wanted to do all my training based off the Quarq but somehow I can't pick the Neo for the resistance in Zwift when I do that — do you know if I can use the ERG feature without selecting the trainer's powermeter?

usr
Posts: 1023
Joined: Thu Mar 25, 2021 5:58 pm

by usr

My Zwift setup reads Favero and talks to the Neo for resistance control. It's Zwift on a Windows PC, with an ANT+ dongle, and I usually pick ANT+ over BLE when there's a choice - but I would not rule out that some of the things offering both are connected on BLE.

Works fine in free ride and the like, I'm not sure if ERG stuff might perhaps be better if I selected the Neo for both read and write. Better as in faster feedback from rpm to resistance which I imagine could be better than my setup, but I don't have any comparison and I rarely do ERG workouts anyways. When I do it's mostly injury related and then I'm not much of a seeker of quality. But does Zwift even do something like handing over the ERG control loop to the device in a setting like that, or does it always send a resistance control signal based on incoming data? If it's the latter, there will be no difference between "native trainer watts" and separate powermeter watts.

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