Since it's done by the head unit from gps, one would like to imagine they're smart enough to only use flat, straight sections with solid gps signal to do the auto calibration from, not trying to do it…
I never auto calibrate. I found it not accurate. I lay a tape measure down and roll the bike with my weight on it to measure the wheel circumference. Millimeters tapes are easier to find know. I got a…
I actually just checked the circumference value auto-calculated by my Edge 830 last night on a road bike and found that it was short by 60 mm. So that means that the Garmin thought I was riding at a slower…
Set it to manual, then back to auto. That will force a new auto calibrate.
Best auto manual calibrate I've found: Toothpaste line on the road. Ride straight through it, measure distance between line and the mark it leaves next.