- I am not making a claim either way. I am starting with questions and a supposition that it might matter due to the comments I have read about trainers and gearing driving flywheel speed over the years.
Not sure exactly what cassette you have to identify exact gearing (number of teeth for each cog), so that is still an unknown even with the “gear” number as a starting point. Also knowing which front gear you used (again, tooth count) is useful for at least general consideration. Here are some general guesses just to try and show the possible impact:
Shimano 8-speed cassette CS-HG51 = 11-13-15-17-19-21-24-28
- ERG with 34t x 24t = 1.42 drive ratio (typical small ring and your 2nd easiest gear)
- STD with 34t x 15t = 2.26 drive ratio (typical small ring and your 6th gear)
- 2.26 / 1.42 = 1.59 = 159% increase in flywheel speed
- ERG with 50t x 24t = 2.08 drive ratio (typical large ring and your 2nd easiest gear)
- STD with 50t x 15t = 3.33 drive ratio (typical large ring and your 6th gear)
- 3.33 / 2.08 = 1.60 = 160% increase in flywheel speed
Pure examples above that may not match your actual use, but the delta in drive ratios above sure could lead to a different “feel” with the notably faster speed at the rear axle from your STD gearing in use. Most people find that a faster flywheel feels “more like outside” with some claiming it is “Easier” as well when compared to lower gearing (like your ERG use).
I won’t make a claim to better/worse or harder/easier, but I will state that the differences of that magnitude are likely to be felt by the rider in one way or another.
Your calibration gear will not impact results in any way. What might matter is how you are setting you FTP since if you test in one gear range and training in a different one… that delta could impact your RPE and “feel” between testing and training.
To be honest, I think trainer mode matters a lot less than gearing. I’d bet more money that deltas between max/min gearing (and related flywheel speed) will make more difference for people than the actual trainer mode. So pick the mode you like best but pay attention to gearing if/when you try to compare modes. Not matching them within reason means you introduce another variable besides the mode alone.
PS, another factor that may come into play (and is often overlooked or straight up unknown by many) is that many trainers will have more power data deviation as flywheel speed increases. The key testers have shown that there is more power tolerance range at higher flywheel speeds. So on top of the actual flywheel speed delta, there could be a power data reporting issue that skews the results of what it “feels” like at higher speeds.