GPS Elevation - Difference between device and online file

[dirt lover]

Currently have a Bryton rider 30 and decided recently to start uploading my rides online just as an easier way of tracking total distance, ride times, etc, than manually recording it. On a ride yesterday though there was a significant difference in the elevation gain recorded on the device and what it said I completed when uploaded. When viewing my ride history on the device, it says I climbed 757m while on the Bryton website it's saying I only climbed 638m. There's also a similar difference in the recorded elevation loss but it's an extra 10-15m out. I'm not too concerned which is the right measurement, although will feel better if it turns out I've climbed more, but any ideas on which data to trust?

 

[Comic Book Guy]

but any ideas on which data to trust?

No idea as I don't know how the website massages the data before displaying it. If they overlay the data onto topographic maps and use the maps elevation data then I would say the website would be a bit closer to the mark.

It doesn't surprise me that you got such a difference. GPS elevation is notoriously unreliable and is normally out by 15m minimum (it is routinely worse than this). Here is some info from the Garmin site indicating that the error can be 400ft (approx 120m): Garmin elevation info.

Hope this is of some help.

CBG.

 

[John U]

Do you give the unit a bit of time to find all the available satellites before you start your ride?
If I just turn mine on and go the elevation can be way off, putting me at 50m below sea level sometimes, and it can remain like this for quite a bit of the ride. When I give it a bit of time to find itself before riding it's usually more accurate.
I'm using a Garmin Edge 305. Been using it for about 7 years. I've checked it against topographic maps and it's been reasonably accurate elevationwise in the past when I give it time to get located.

 

[SlowManiac]

I think it depends on a couple of things:

Does your device have barometric altimeter? This is the most accurate - GPS altitude is crap.

Does the site you upload to have altitude correction? Strava has this as an option but I notice that it is not completely error free. For example on one of my routes I can upload a ride and it looks fine. Then if I use Strava elevation correction it messes up a particular section.

 

[dirt lover]

Worked out it was most likely just error in the GPS elevation recordings. Compared my data with a friends who's done a similar ride and the online elevation was fairly even with his. Never had the issue before when doing the mostly flat commute to uni so guess it's something new when starting to go over slightly hillier terrain, thanks for the help guys.