I’ve a Garmin 800 and always get a much lower total elevation ridden on it compared to when Strava auto-corrects. The different is usually a factor of 2. Any ideas why?

Probably because the Garmin uses barometric data whereas Strava will estimate your altitude based on your track and it’s mapping data.

I’d have thought that Garmin would use satellite data rather than a barometer.

Satellite positioning is only accurate (to15mm or so) if atmospheric conditions are taken into account, otherwise it’s nearer 4 to 5m E, N and elevation, hence why your sat navs have your car icon going up a slip road of a motorway for a bit when you’ve decided to go straight on along the motorway.

Usualy its the other way arround, strava tends to flatten small changes in elevation.

Usualy I’d believe the garmin, I checked mine against an OS map for a fww rides and it was within within +/-5%, Strava was arround -40%.

Total ascent on strava is always less than what is on my bryton somtimes by quite a big margin!

Bolt

Strava flattens out the ride from my understanding so total elevation recorded is often slightly less than actual.

In mg experience Strava seems more accurate than my 819. I’ve kept an eye on the total ascent when climbing and watched it jump 5ft at a time when I’ve maybe done 1. Or maybe the red at GT does have 4,000ft of climbing…?

Strava uses digital elevation data, so on routes where you are either climbing or descending I’ve found it to tie up pretty well with friends garmins. On routes with a alot of undulations (like trail centres) I find strava underestimates.

Probably because the Garmin is actually accurate

If your garmin is using gps it will be very inaccurate. Strava will interpolate the route with something like SRTM data, this means it will still be pretty inaccurate, but fairly indicative. I keep meaning to interpolate one of my gpx with OS landform panorama data to see what the difference comes out as, I don’t have access to anything more accurate such as landform profile or nextmap DTM though.

https://strava.zendesk.com/entries/20965883-Elevation-for-Your-Activity

Garmin 800 uses barometric which should be very accurate, provided it’s calibrated. Otherwise, you may see significant drift during the first 20 minutes or so of riding.

Strava will do it off mapping data. This is particularly error prone on tracks that cross the side of hills, as small errors in position can lead to large errors in altitude.

Generally I’d trust the Garmin.

see my post in this thread

Elevation data on GPS and Websites

Strava will use barometric elevation data from a GPS that supports it. Different websites apply different amounts of smoothing to that data, so that the value you see on the GPS screen will almost certainly differ from what you see on a website.

Some Garmins can be set to do elevation from air pressure and / or satelites I believe. You do have to calibrate the barometer though.

It is odd. When I download garmin to strava, invariably, strava shows lower ascent and descent. Wherever I have ridden.

Garmin definately seems to flatten the rides, doesn’t matter whether on the mtb or roadie. Did a bigish road ride yesterday, the garmin gave 1100 m climbing over 130 km, strava about 2200 m climbing. Maybe it is the calibaration on the garmin.

The only thing that needs calibrating on the Garmin is the current elevation at a specific point. That won’t affect total ascent/descent at all, only the absolute altitude.
Unless it’s changed, all the Garmin does is sum up all the +/- changes from 1 data point to the next. Any “smoothing” or interpretation is down to how you set up the logging… Auto? Every N seconds?
And then when you stick it in Strava / Endomondo / Mapmyride / etc. they then do their own interpretation of something that’s already probably been reduced according to an algorithm in the Garmin.

In short… total ascent/descent is unreliable.

When people say “i find my iphone accurate” or “strava accurate” etc… what are they actually using as a reference? Manual check of an OS map? or another app that interprets and smooths data?

a value half or double that reported via another app/website is pretty normal IME.

Just checked today’s ride
Map says 440m up / 425m down
Garmin says 385m up / 368m down
Endomondo says 398 up / 368m down

One of them is more right than the other. The start+end points are not the same and should be 15m difference.
Last time I used Strava it made extra total ascent up even from the same data file.

Just enjoy your riding and Don’t worry so much about it. Life’s too short.

Garmin definately seems to flatten the rides, doesn’t matter whether on the mtb or roadie.

that’s what I’d expect with a coarse elevation dataset like SRTM.

When people say “i find my iphone accurate” or “strava accurate” etc… what are they actually using as a reference? Manual check of an OS map? or another app that interprets and smooths data?

Count the contour lines crossed, divide by 2, multiply by 5m (or 10m or whatever the map is showing). That’s worked with both a Edge 305 and an 800, so I’d take the satelite data as being moderately accurate too. We had an old walking GPS on our boat as a backup (so should have read ~0m at all times) and it only ever recorded a few 10’s of meters in an hour, an insignificant ammount compared to an actual ride, unless you’re riding in Norfolk.