Hi,
I have an autosync to Stava from GC, mainly to participate on Strava with more friends and my team.
I not only notice a big difference in things like elevation and calories used between the two, but between Garmin device elevation and "Elevation fix enabled", also between myself and friends the difference in calorie usage is huge.
Firstly elevation...my device (500 and 910xt) always report very much on the low side...I can see other people who ride the same route and difference is not a few meters, but more in the 100's. Strava on my last ride had the elevation at 1400, GC and 1000. That's a 40% difference...so not even close.
The other one is calories burnt, now I know this all depends on weight, height, fitness and is in general an educated guess!! But again mine in GC is on the low compared to Strave, again out by 100's. But not only that...again compare to other users, who have entered in their details (weight, zones etc). Compare to people who are in my group, so similar fitness, size etc and they apparently use considerable more chocolate bars than I do!!! Then I look at people who run/ride the same group as me, but are considerably fitter/faster and are normally in a higher group...and they too burn more calories...even though they are clearly going well within themselves.
I guess the only thing that can be said about the calories is a) does it really matter...probably not...but when you're trying to knock a kg or 10 off...it does!!! b) it is consistent...I am always on the low side. That could be my make up, but Garmin doesn't know that (and nor do i!)...it takes weight, HR, zones etc etc and gives a number...so similar numbers should give similar results.
What gives!!!??