I happen to have a Kickr bike and Vector3 dual power pedals so decided to test these together after reading this monster of a thread.
tl;dr - gear selection in ERG mode, on a Kickr bike, makes no difference to recorded hr or power output but makes a massive difference to ride feel, RPE.
You can give the Kickr whatever gearing you like so, for this test, I flipped between 56x10 and 30x36 each sweet spot interval, starting in 56x10. The workout was Geiger +1 - it has 4x12 min SS intervals that vary a little throughout each interval, average the same.
This is the ride as recorded by TR on my phone, connected to the Kickr bike:
And this is the ride as recorded by my Garmin 520+ connected to the Vector3’s:
HR was from a Garmin chest strap connected to both recording devices, Vector3’s were calibrated before the test, Kickr bike doesn’t ever need calibration.
Interesting things to see here:
- The Vector3’s are ~15w lower than the Kickr bike.
- Average power, HR, cadence were close to identical between the intervals, gear selection made no difference there.
- The Kickr power numbers are bogus. In the recording it looks like a really nice smooth power line exactly following the workout design, that was absolutely not what was happening in real life. It’s as if it doesn’t matter what power you actually output while in ERG mode, the Kickr will only report what power it thinks its resistance should be producing.
- This can’t be explained even with something like 10s smoothing somewhere in the recording chain as there were portions (like around 29 or 43 mins) where, after shifting gears between hi/lo, it would take the ERG ~30s to adjust - this shows up in the Vector3 recording as an extended power drop/spike.
- In 56x10 (1st and 3rd intervals) the recorded power variability is high but the cadence variability was low.
- In 30x36 the exact opposite was true - power output looks a lot smoother but the recorded cadence is all over the place.
- Subjectively, 56x10 felt good to ride in - solid, meaty diesel-engine power generation. 30x36 felt utterly horrible, kinda like riding uphill on wet leaves. It was as if it was only letting me generate power at the top of the stroke before slipping then forcing me to overcompensate after the slip to get back up to power over and over and over and … It was so gross I nearly cancelled the test after the first 30x36 interval. While, bizarrely(?), this didn’t lead to any meaningful HR difference it did make the 30x36 intervals feel harder.
So … WTF? Looking at just the recorded power you’d conclude ‘ride in 30x36 if you want to be smooth / stay in-zone’ but that would 100% be the wrong choice. By far the smoother, easier ride, was to be had in the higher gear … I’ll be using big gears for all workouts in future.