Like Chad, it would be helpful to understand what power your Garmin is recording. Our assumption right now is that TR is recording power from your Saris H3. And Garmin is recording crank or pedal or spider power. Is that correct?
One of the better explanation I’ve read about the difference between Erg/Resistance/Outside was from two blog posts (CTS and Joe Friel). The basic idea is that you have a dead spot in your pedal stroke, at roughly 12 o’clock and 6 o’clock. At 90rpm you are hitting that dead spot 10,800 times an hour. When riding outside on flat ground at a reasonable speed, your momentum carries you through that dead spot and its not noticeable. On the flip side that dead spot is very noticeable in a few situations:
- outside at very low speed, on a steep climb
- inside on a dumb wheel-on trainer
Inside on smart trainer with a heavy flywheel, like your Saris H3, its less noticeable. The best way to simulate that dead spot is to use a low gear (small chainring). Erg complicates things a bit, as it is actively responding to your power and cadence changes, however many can notice a small “dead spot” in the pedal stroke in Erg with small gearing on a smart trainer with a heavy flywheel.
Ok, with all that said overcoming the dead spot does appear to impact pedal efficiency (but not average power) which many can feel as having to more actively pedal around the clock. Or you may not notice that much. It seems that it is impacting to you on certain workouts.
As Chad points out, best practice is using the same gearing for ramp testing and inside workouts. And same power meter inside and outside (TR’s PowerMatch).
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Wow, no I wasn’t. I’ll check it out. I’d love to get a single set of power readings. Thanks for this.
Joe
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Yes, that’s correct. TR is recording power from the H3, and Garmin is reading power from the crank. I’ll use the PowerMatch to get a single power reading.
Joe
FWIW, I test, train in the same front gearing as what I usually ride outdoors — large chainring. I want the “feel” pretty close regardless of testing, indoors, and outdoors. If I would climbing regularly I might go small ring. I always use ERG and did find the small ring more fatiguing.
If you head down the PowerMatch road, make sure to include that aspect in your next FTP test. Essentially, dial in all your preferred settings, test that way and train using it that same way for most of your workouts.
Consistency is key here, like it is in many other avenues of this sport.
Another FWIW, recently I did a 10% grade at 4-7mph / 70rpm as a 20-minute field test. Comparing that climb to the ‘feel’ of my Kickr - on the Kickr the big chainring feels more like outside even on climbs (TR PowerMatch on my direct-drive Kickr, very similar to your H3). I don’t do those climbs very often, however training in the big ring (inside and outside) has never been an issue with going out and climbing. To me, the little chainring on my Kickr feels really weird, power is unnaturally smooth and I don’t use it at all.
First impressions after buying a Kickr and using it on Zwift:
Still does feel weird, I just don’t notice it anymore. 
Its really a personal choice, on what feels ‘right’ for you.
“Another FWIW, recently I did a 10% grade at 4-7mph / 70rpm as a 20-minute field test.”
–OK, that’s just an exercise in suffering.
But I agree that the big ring on the trainer just feels much more like it does when I’m riding outside. I’m glad the consensus of this discussion has been to switch to the big ring.
joe
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I’ve just gotta ask at this point. What’s going on with the white boxes in your posts? The number has grown from one to three. 
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Thought it made a statement, in a good way, and glad you asked.
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I dunno. I’m perennially computer cursed. It’s unreal.
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Computer cursed? Well you made my Monday which is always the worst day of the week. Provided some much needed entertainment, thank you!
I still can’t figure out how it happened… or if you or your computer were sending a secret coded message:
Another unsolved mystery Like my wife’s iPhone won’t let her type “Well” at the beginning of a message/text (yes we’ve reset adaptive and related settings). And they said computers were going to save us time!
