I’m getting very different readings depending on which bike they are attached to. Which makes no sense.
The only difference being crank length that I change on the head unit.
very strange, I’ve not tried switching bike, so not experienced this. I assume you are recalibrating? Could you have different drive train loss between bikes, impacting PM on Turbo Trainer
This could be a genuine explanation. Whilst reading comments further up, my immediate thought was that pedals and smart trainers measure the wattage at different points. Although this should really manifest itself as a marginally lower reading at the rear axle vs the pedal.
Yeah tried recalibration on just Garmin… Then via app and Garmin (even tho they say head unit is all you need).
I’m going from 1-2% to 15% or more… My TT bike definitely has a chain attached 
That was my thinking to. My old power tap read very simialr to my flux 2 based on HR and RPE.
I’m sure it’s buried in here somewhere but Jorgan or any others using the Favero Assioma pedals, how is the accuracy compared with your turbo?
A friend in my CC is thinking about getting some.
I don’t use them but from most commenters, ie GPLama, they are pretty much a gold standard for accuracy. When my P1’s die I’d probably get them. Downside for me is its another thing to charge and I love the P1 has just one AAA battery each side so could stop at a shop in an extreme situation.
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cheers
My first lot of comparisons I was generally within 1% from sprints up to an hour.
Then I put them on TT bike and I’m 15-20% out (same pedals, same turbo).
Other than changing crank setting on head unit… No idea why they would now be different
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Battery life is also very good on them I think. I only charge handful of times a year and usually not empty just thought had been few months. I ocne started a long ride when thebattery alert came on the garmin and they lasted 4hrs and didn’t die.
I’ve tried mine on 3 or 4 different wattbikes and found them essentially identical
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From the Assioma users on here apart from @mw22, @jeffb may be able to comment on the accuracy, but @Jorgan & myself both use dumb trainers.
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Thanks. I was forgetting that. I’ve also pointed him GPlama’s direction.
Correct, I don’t have a smart trainer to compare them against. Read higher than my old P2Max…but then so does everything!
Battery lasts forever on them; even IM training I wasn’t charging them more than once a month.
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I’ve only used them a bit on the Wattbike while the built-in PM was broken, they seemed quite good but it was hard to compare them with anything, power seemed about what I would have expected at the time.
They’ll be going on the TT bike when I get it out of the loft.
Do you think the P2M gives a lower reading as well? My stages and my Tacx Flux read around 10-12 watts higher than my P2M but could never be sure which one to trust as it would mean swapping out the rotor chain set and BB for my stages chainset
I think it was well known that it read a bit low. Very consistent though and never let me down.
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I only have P2M’s (two of them) but would agree they both read a little lower than three different smart trainers I’ve used (including a Kickr and currently a H3). Difference is about 10w also.
I think that’s frequently why best bike split gives me a cda figure that I just don’t think is realistic. It’s assuming I’m more aero than I am as I’m actually putting out a tad more power than the file suggests
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Thanks for reassuring me it makes sense now when thinking about the data when I trained on Zwift and the data from the Tacx. Now that I am outside again then P2M rules so I will have to try harder to replicate the watts.
Got some Favero Assioma UNO pedals coming my way 
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They’re here and on the bike.
What do folks have on their displays? (I have a Garmin 735xt) I’ve seen that Avg Power, Avg HR, Time, Distance is good for race day…