Vivoacive 3 for Mountain Biking?

If all you're doing is mountain biking, then you don't want any watch. You want a bike mounted cycling GPS like an Edge or an ELEMNT. Watches simply have the wrong form factor for cycling. There's nothing that doesn't work (well I'm not sure if the VA3 does power meters, but that usually isn't a problem mountain biking), it all comes down to how small it is and where you're carrying it. You just can't see them whenever you want, and in cold weather you make a choice between heart rate (under clothing) or visibility (over clothing). A Vivoactive 3 will work (there's nothing different with ascending or descending on the road or on trails), but compared to the experience you'll get with a proper cycling head unit it isn't even close. Now if you have other activities in mind, that changes things, but a watch is definitely a big compromise for cycling. My solution is to have an Edge 1000 for road and mountain and an Epix for other outdoor activities, and I use the one that works best for that activity.

schinder But if road biking won't differ from mountain biking, why do some garmin wearables have mountain biking as a preloaded activity along side biking?? Why does the Fenix have mtbing while the VA3 doesn't?

I'm not sure what the specific differences are between biking an MTB on the Fenix, (my only biking is riding around the neighborhood), but it could be both how it's ID's when updated to GC or be what data is uploaded or available to be shown on the watch and in GC.

Another thing to note about "why on a fenix but not on a va3", is the Fenix is the top end wearable device in the Outdoor Group, and the va3 is kind of the midrange and is a fitness device (Forerunners are also fitness, but more running orientated.) The fr 23x/630 don't have a native walking activity for example, so things differ. You'll not find a number of things on the va3 you find on the fenix 5/fr 935 (a well know one is open water swimming. You also have more sensors available on the f5/935 - IIRC, things like some of the bike sensors.

I use my watch on MTB and road cycling for recording the activity only. Connected with speed, cadence and HR-strap it does it job quite well. But I never take a look at it during an intense ride as it is very hard to read. I use the outdoor cycling activity for both types of ride and I don't think there would be a real difference if they were seperate activity types. Only after uploading to Connect I have to change the type from general Cycling to MTB or Road manually. No big deal.

I used to use a bike mounted computer but since buying the vivo3 haven’t used it. I found I was to busy looking at information that didn’t matter. Haha
i ride both mt and road with cadence sensor. The only reason I could find going back to mounted comp is if you don’t know the trail, then you can have directions where you can see them. Now I’m more focused on the ride and can look at info when connected at home.

Well I have a Edge 25 and the Vivo3, the jury is still out as far as I'm concerned, one trail at the weekend had a 4.30 time with the Vivo, but 3.15 for the Edge, the vivo picked me up as on the trail at the trail head and started the timer. This was the same on all trails,VA3 just not as accurate as the Edge. However I've just realised I didn't have Glonass enabled on the VA3 so that may explain the difference.
Also the VA3 connection to my ANT+ sensors is much flakier that the edge. The edge just connects and that is it. Pre firmware update the VA3 couldn't even detect ANT+ sensor at all. After an update it managed but on my latest ride it kept dropping the connection and re-connecting.
All in all the VA3 is not a very mature product and I've suffered allot of teething issues, as cycling is not it's main focus it may take a while for those issues to be ironed out.

There is a pre loaded app for mountain biking on the VA3 as well as several other hidden gems. Before I switched to the FR935, I had mountain biking, spin biking and martial arts added to my activities. Go into "settings" and then "activities & apps". Scroll to the bottom and select "add". From there select "create" and then select "bike". Scroll down and select the activity you want added. There are several "hidden" pre loaded activities you can add after selecting create and then picking an existing activity.