when on a ride last night i noticed my edge 800 said id only done 1100 feet of climbing, thought it was a bit odd as i was fairly positive we’d done more than that…..

anyways by the end of the ride it came in at about 1300ft ascent…again me and my mate were puzzled, hes uses his phone (which is innacurrate also), but it we couldnt understand how mine said so little….

i plotted it on bikehike and the elevation said 2634feet of ascent, which IS exactly around the figure it should have been (and usually is)…

so any ideas why my edge800 has lost 1300 feet climbing? or just not bothered to record it?

FWIW it worked fine on sunday, and ive owned this over a year and its never done this before

AFAIK it had full signal strength when i set out

Have you uploaded it to Garmin Connect? If so, check the “elevation correction” option and see if that makes a difference.

I find my 800 tends to under-read climbing data when the weather is crap (rain etc). Low pressure I guess.

If it is raining then sometimes the sensor hole can get blocked with water

It’s because the elevation is not calculated via the map, it’s from the atmospheric pressure so it can give big fluctations. There is a significant difference in the elevation of my house depending on the weather that particular day, it’s often below sea level! Only way to get a really accurate read is once uploaded to the computer and having it corrected.
More info here

The weather points make an interesting read i must say! it was indeed pissing it down last night for most of the ride!

thinking about it i looked at my comp on the first few climbs and it went to about 600ft as we climbed, so it was working when sunny!

then the heavens opened and by the time i looked at it again probably an hour on or some we’d only got to 1100 as above….

its been totally accurate (or at least consistent, if a few feet out) in the past year, just this one blip!

guess the weather could well have caused it then, as they were pretty awful conditions!

I think the 800 uses barometric pressure to estimate amount of climbing, which is much more accurate than GPS estimates. The fact that the elevation of your start point changes with changes in atmospheric pressure doesn’t really matter as the amount of climbing depends on changes in height. However, if the pressure changes during your ride (i.e. a low or high pressure front moves through) then this could cause it to under or over estimate the amount of climbing. In which case the amount of climbing and descending would normally be different (unless you got really unlucky). So, if you start and finish at the same point, you can just check that total climb and total descent match.

Cheers,

Andy

I thought the whole idea of having a barometric altimeter built in was so it was more accurate than elevation correction. I think the trick is to turn on your Garmin so that the starting elevation is ‘settled’ before you start.

ive been around 100m below sea level at Brechfa before!

Yep, heavy rain does seem to cause it to undercalculate altitude

I was suprised at how little it recorded during my attempt at Kielder last year – just 1,422m for 83 miles. This year (no rain) it was 3752m for 100 miles. The last section had a few killer hills, but not that much

Setting the Elevation correction on Garmin connect does seem to do the trick – 100 mile drops to 3431m, 83 is almost doubled to 2697m.

Heavy rain always used to affect mine, I think water gets in the sensor hole and causes it not to work effectively. The sensor is a small hole on the back of the unit just below the G of the Garmin logo.

Best thing to do is get the Garmin silicon case, it stops water getting in the sensor and I’ve not had any issues with the elevation in heavy rain since I started using it.

It’s also possible if you know the elevation of where you usually start your rides to manually set the elevation for a saved GPS location.

The barometric altimeter is pretty accurate at measuring changes in elevation, but it can’t tell you your actual elevation due to changes in atmospheric pressure. To get around this, the device uses GPS to calibrate the barometric altimeter, but it does this quite slowly. If you turn the GPS on and start using it immediately, then for the first part of your ride the altitude will be drifting as it calibrates to the right altitude. This can lead to either an under-read or over-read in your ascent.

The way around this is to either leave it standing until the altitude settles, or program a waypoint with the actual elevation. If you press start with in a 30m (I think) of a point of known elevation, it will calibrate to that immediately.

Very interesting guys thanks for the info….

Few points which seems to tally with the points you all make

I started riding instantly after turning it on, I think it had satellites/signal connected but can’t be 100% sure

It also Absolutly pissed it down for a long period of time, also driving rain so could have easily blocked the sensor…

And maybe as someone else has pointed out, I have over summer stopped using the silicone cover! I used the cover all last winter, and never experienced this, so I may just Bung it back on….

So It’s quite probable the symptoms I experienced with lack of height certainly could be caused by the above according to you folks….

So I’ll cover it up i think is the best solution

Have you calibrated it? You can do this in the settings menu. Get your location elevation from an o/s map and see if that makes a difference. Mine has given consistent readings (within 50ft) on a standard route in all weathers.

+1 for the Garmin silicone case, the problem is caused by water blocking the barometric sensor holes (it was much worse on my Edge 705, and Garmin would never admit there was a problem).
As for calibration, if you start a ride within 30′ or so of a known mark, the altimeter will calibrate to that mark. I start most of my rides from home and I’ve set marker and corrected the elevation (210′), when I press Start the elevation corrects to 210′. I have another mark at work (35′) that corrects the elevation for my commute home, you’d be amazed how much the barometric pressure can change during a 12hr shift (equal to 500′ a few weeks ago).

See page 40 of the User manual.