It’s only a few months old, just finished another ride and its 25% over reading compared to everyone else.

No rain today so not a blocked sensor, in sure it used to be ok. Nothing definitive on Google search but it doesn’t seem an uncommon issue.

Any tips before I have to work out where I bought it and send It back?

Mine’s cobblers too. The gradient % is all over the place as is metres of ascent.

When you use the “actual climb” or whatever it’s called on the Garmin homepage, does it correct itself?
Mine differed by about 15%.

Coincidentally, I’ve just been reading some stuff on a forum about Garmin routing prior to trying out my new Edge tomorrow.
Several people on that thread seemed to flag up some properly weird height gains so it’s clearly not an isolated issue.

Newer Garmins seem to have tried to pack in far too many clever features and want to tie you into Garmin Connect (which is dreadful). I’m wondering if it’s a combination of slightly incompatible/different mapping formats – OSM, Google, OS – along with Garmin’s overly complicated, trying-to-be-helpful routing features that screw up the whole calculation.

I’ll post back tomorrow. Will try and follow my downloaded route on the new Edge but I’ll take my old 500 with me too and see how the readings compare.

I’ve compared the 705 and 810 against my old Polar altimeter that I always wear. The 705 gradient reading is sensible but height gain overstated whilst the 810 gradient reading is all over the place and the height gain is overstated. The Polar corresponds (mainly) with height gains calculated from mapping tools (Memory Map etc).

My 810 was convinced I was around 50ft below sea level on a ride once. I was on a ridge looking down at a river so I’m pretty sure I wasn’t.

My 800 goes loopy in wet weather. Water in the pressure sensor. Take off the rubber case if you have one and put it somewhere warm and dry for a bit.

Might be clogged up with mud?

Great, new toy than may not work. Still trying to set my sodding 810 up. Does the Bluetooth connect and then disconnect every so often, rather than stay connected ?. I will take my old Bryton and 810 for a ride this weekend to see what difference I get/ in case I cant get the 810 to work.

Plenty of 510’s are the same,iv’e seen riders have 50% extra elevation on strava because there’s been a low pressure that day .

My wife’s 810 consistently under reads by 25% vs my 510. Distance spot on but ascending is screwed.

Still at least it’s consistent.

I would imagine windy / gusty days might confuse the pressure sensor. Maybe that’s it?

GPS devices very poor at altitude and gain/loss, the pressure sensor is generally better but still not great. The pressure sensor needs to be recalibrated depending upon the weather. I sat at the top of Scarfell Pike and watched as altitude changed constantly until finally it settled on the correct number. Its my view the numerous small errors in gps position left/right make little difference but the same up/dpwn errors cause the total,ascent/descent to be overstated.

Yarp, my old 810 suffered the same problem, over read by anything +/- 15%, kinda got used to thinking I was climbing Alpy DUuz.. When in reality it was Old Beacon Hill..

Garmin devices with a barometer, while more accurate in theory, really must be calibrated before every ride.

You need to set locations with known heights. Even then I’ve seen a loop start at one height, back to original location and end up 50ft lower than it started.

If you sync to Strava it will likely do some adjustments based on topographical data Strava use. Or on the other hand it may not because you have a barometer and then you’ll see a difference compared to all the smartphone users who get their data corrected (though which is actually correct is another matter).

If pressure changes then you will see a change in height from the barometric ones. Hence a ride can easily finish at a different height to where it started, your house can suddenly end up 100ft below sea level, you can climb 50ft on the turbo etc etc.

I use the height gained rather than the actual number for that reason. My 1000 seems comparatively Accurate (or at least plausible) a friends 500 added 10% on a recent ride when uploaded to Strava.

I find mine to be most inaccurate for elevation gain when I’m riding near the coast , the altitude is way off

Interesting – just been for a short local loop with the new Edge on the bars and the old 500 in a back pocket.
Both GPS were left running the whole time, no auto-pause. Both were started and stopped at the exact same time in the exact same location.

Both recorded the same distance, the new Edge showed 606m elevation gain, the old 500 said 656m. 50m out, not too bad.

Uploaded the new Edge to Strava (direct upload from the .fit file, not via Garmin Connect) and Strava has done it’s usual auto-correct and shows 1566ft / 477m climbing. I’m wondering where my missing 129m have gone…

It’s bobbins. There were several of us riding, mixture of Garmin, iPhones and android, everyone is pretty similar but my Garmin is way over, does it every time.

strava link

I can’t find any options to try and correct it, you used to be able to run it through a correction progrmme, I live on the coast, perhaps the barometric pressure varies more here?

They really need some competition.

The other thing to think about is how often the Garmin ‘samples’ altitude data. Hypothetically, if you rode 1 km on a sinusoidal (up-down 1-2 metres or so) rolling road starting and finishing at the same elevation, you’d have elevation gain even though you never actually gain height overall. So if you’re riding very undulating terrain and the Garmin is polling more frequently than Strava, it’ll display a greater elevation gain figure.

As far as correction for altitude, I’m aware that you need to correct in order to get accurate absolute elevation data. But the total ascent / descent shouldn’t really be affected (I think).

As Deadkenny says setting known heights is a good idea. Even better if the start point has one so that the device can “find” it before you press the start button and ride off. I programmed heights for work and home on the commute and the gains/losses are more consistent now.

I have my “Home” elevation (and a few others) set if I press Start within 40 or so ft of any of these points the elevation on my 810 is rest to the correct figure.
The 810 uses a combination of GPS and barometric altimeter to come up with its elevation reading and over time it gradually corrects itself, but it’s better if you start with the correct elevation in the first place.

+ 1 ^^^

I told you. We just ride harder, further, and higher than the others.

DrP. Edge 800 user..

The way I read the calibration feature, I thought all it did was set the start point so that you start at the correct height rather than it starting below sea level (as is usually the case).

Seeing as I was only really intersted in gain I have never calibrated it.

And seeing as the landscape is pretty flat where I live, and I tend to try and ride up lots of short ‘climbs’ between cliffs along the coast… and isn’t the height map resolution for the UK something like 50m so correcting the data is going to smudge out all the smaller climb detail anyway… So I don’t tend to correct the elevation data.

Recent ride:
garmin edge 510 18.1mi 3:16:30 2182ft
garmin forerunner 210 18.2mi 3:15:25 1556ft
garmin edge touring 17.2mi 3:13:26 1595ft
strava iphone app 18.3mi 3:21:05 1624ft
strava android app 18.1mi 3:31:35 1626ft
strava andoird app 18.3mi 3:22:31 1623ft

Todays local spin out in the mud, I took both my old Bryton Rider 20 and Garmin 510 out and the readings are :

Distance Bryton : 16.31 miles Garmin 16.1miles

Elevation Bryon : 500 ft Garmin 577 ft !!

Max speed Bryton 24.2mph Garmin 24.6 mph

sirromj – Member
Seeing as I was only really intersted in gain I have never calibrated it.

Same with me. Not really that fussed about the height accuracy, so long as the gain is reasonable.

It’s never going to be perfect though. Barometers are affected by pressure changes, and GPS altitude is far less accurate than positioning.

In many ways topographical data correction that Strava does is perhaps better. Sure it’s not spot on as that 10 metre square you’re on may actually be 10ft higher or lower than the data plus it’s not fine grained enough to account for all the small undulations.

On the other hand though it may be more consistent. If it’s giving me the same kind of data between rides for the same device, and comparable with others then that’s good. Though I still find wild differences between other people on the same ride. More so in altitude, but even distance can be a mile or two out and many of us are using Garmins!

Oh, and on distances, there are differences if you use a speed sensor also. It’s more accurate as it clocks up wheel distance but may turn out to be more or less than expected compared to those just using GPS.

Whilst it’s true accumulated height calcs based on barometers are subject to pressure variations, this does not explain why my barometric Polar altimeter is much more accurate than my barometric Edge 810 when it comes to accumulating height gain.