A little long but bare with me!!
I had really had my distance under-reported on my favorite mountain bike trails. I bought the garmin speed sensor. I chalked the wheel and measured it on my driveway with a tape measure. It came out to be exactly 91 inches. I entered the wheel size in my 5x+ as 2311.
I measured a partial loop and a full lap with riding.
And the partial loop with running.
Here is what it looks like (this was 2 laps recorded with 5x+ only). It was really shorted on distance.
https://connect.garmin.com/modern/activity/2927775698
Here is what is crazy
Full Lap:
5x+ with Speed Sensor full lap = 8.52 miles
705 GPS full Lap = 7.65 miles
830 GPS full Lap 7.5 miles.
Partial Lap
5x+ with Speed Sensor partial loop = 4.6 miles
Run: 5x+ with Stryd partial loop = 4.25 miles
705 GPS partial loop = 4.18 miles
Run: 5x+ GPS partial loop = 3.88 miles
So the thing that shocked me was the 8.52 miles. The trail is a lot of small climb and drop (25-30 feet up and downs).
Would that small of elevation change account for almost an extra mile? Doesn't seem like it.
Did I calculate it right? I am positive I measured the wheel right.
So it dawned on me that it may be hitting roots is registering a wheel rotation.