Extremely wrong ascent value (twice the real one) for MTB activity

In my experience of doing a lot of testing of the Ascent feature during road cycling, is that the Ascent is always less than the actual elevation gained because of the buggy algorithm.  So if you ride up a 100m hill where the altimeter starts at 0m and reaches 100m and correctly increments the altitude for every 100m on the display, the total ascent will be something of the order of 85 to 90m.

I can climb and watch the Fenix 5 display increment the altitude display but not increment the Ascent.

In my experience the Fenix 5 is useless if you want accurate Elevation Gained.

Your situation may be that the algorithm just sees too much climbing with the potentially more jagged MTB type of climbs.

BTW I spoke with Garmin Support in UK about this and they failed to understand the difference between barometer based altitude data versus GPS derived altitude data, and said that the barometer readings and Ascent data I was seeing, is well within the accuracy of +/- 100 feet for every reading on the Fenix 5.

I should also say that when I am driving my car, I regularly get a stairs climbing goal award on my Fenix 5, for sitting in my car and performing absolutely no stairs climbing.  IMHO, Garmin do not have a clue about anything to do with altitude based calculations.

Thank you for sharing your experince. My biggest concern is that I could see how the total ascent value was increasing unrealistically while I was going uphill, on a smoothly and continuously climbing route, on quite a wide road, with a good view of sky. Checking the elevation profile for this part of my ride, I found out there are "downhill jumps", 5-25 m, which then causes the elevation gain to be even 100 percent higher than the real one. And this is something I would not expect from a device I paid so much money for.