Speed Sensor and 5x+ - Best accuracy?

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

Bike:
5x+ with Speed Sensor partial loop = 4.6 miles
5x+ with Speed Sensor full lap = 8.52 miles

Bike:
705 GPS partial loop = 4.18 miles
705 GPS full Lap = 7.65 miles

For reference - Brother's Garmin new bike gps

Run:
5x+ GPS partial loop = 3.83 miles
5x+ with Stryd partial loop = 4.25 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.

0 joshtee over 6 years ago

Have you had a chance to do anymore testing? I'd like to see some more comparisons between the speed sensor and the the Fenix by itself. I have a 5x plus and it seems to have suspect distances. Especially in wooded tight singletrack MTB trails. It's always short on distance when compared to other devices. In open areas on the road, it is pretty much same as other devices. When looking close at the Fenix tracks, they usually seem pretty tight and pretty good. Makes me wonder if maybe the Fenix is the accurate one.