Garmin Elevation Differences

[2LeftCleats]

Daughter and I rode side by side yesterday for 43 miles. Her Garmin 500 registered about 2300 ft elevation gain and my 510 showed 3000 ft. Map My Ride is much closer to hers. Any idea why there would be so much difference?

[rnhood]

Map my ride is more inaccurate than either. Check the route on RidewithGPS. It will be far more accurate than Map my Ride although none of these routing programs are perfect.

Its not uncommon to see differences in gain between Garmin units. Its always been like that. 2300 to 3000 is a fairly large difference for 43 miles. Be sure to power the units on for a minimum of 15 minutes before pressing the "start" button. It can take this long to fully normalize and correct the current position once powered up.

[2LeftCleats]

Thanks!

[kramnnim]

There are often/usually differences between Garmin models, and even units of the same model vary a bit.

[dolface]

As others have mentioned, this is an issue with Garmins.

This is a ride that that my buddy and I did, https://app.strava.com/activities/268849536, https://app.strava.com/activities/268840675

700' of difference over 43 miles between a 500 and a 510.

[whatwolf]

I was under the impression you could calibrate them with a known elevation? Is that not the case? I've never tried

[kppolich]

Check to see if elevation correction was turned on also.

[johngmartin]

Related question - I often ride with Strava running on my phone (moto X) AND my Garmin running, and as you would expect, they finish with different numbers. But does anyone know which of the two might be MORE accurate? Which do you trust more - phones or garmins?

[DfCas]

If you uploaded them both to Garmin Connect, as the previous poster said check for elevation correction and see if it is enabled/disabled . It should be disabled for both devices. Barometric altimeters are pretty accurate. The GPS one are wildly inaccurate.

[dolface]

Relavant tweet from a friend who works at Strava: https://twitter.com/mlroach/status/573947013991026688

If you uploaded them both to Garmin Connect, as the previous poster said check for elevation correction and see if it is enabled/disabled . It should be disabled for both devices. Barometric altimeters are pretty accurate. The GPS one are wildly inaccurate.

[LegendRider]

Is the speedometer function similarly inaccurate?

[NickR]

Relavant tweet from a friend who works at Strava: https://twitter.com/mlroach/status/573947013991026688

I've been doing it all wrong, time to use my iphone instead to win the segments on Strava lol.

[shovelhd]

Is the speedometer function similarly inaccurate?

On average, not too bad, but from moment to moment, yes. I like to record speed data so both bikes have Bongrager speed sensors.

[makoti]

Is the speedometer function similarly inaccurate?

If you ride a lot of tree lined roads, very bad IME. Jumps around like crazy. Always use a sensor where I live.

[LegendRider]

On average, not too bad, but from moment to moment, yes. I like to record speed data so both bikes have Bongrager speed sensors.

I was just thinking about this on a solo ride I did on Saturday. There is a hill that I occasionally sprint over to test my legs. Not very scientific, but it works for me.

I crested the hill at 25mph according to my Garmin 200. I don't ever remember reaching that speed when using a simple CatEye computer and I can guarantee that I'm not in the best shape of my life. Bottom line: I question the Garmin's accuracy.

[djg21]

I use an Edge 810 with the GSC 10 cadence/speed sensor. Speed/cadence are always accurate. Altitude is relatively accurate if it is calibrated pre-ride, given that it is based on barometric pressure. I know the exact altitude in my driveway and recalibrate pre-ride if it reads incorrectly.

I've seen some off readings on a few occasions when the weather changed dramatically during the course of rides, but this is to be expected.

[Mark McM]

Daughter and I rode side by side yesterday for 43 miles. Her Garmin 500 registered about 2300 ft elevation gain and my 510 showed 3000 ft. Map My Ride is much closer to hers. Any idea why there would be so much difference?

Had one of the units been recently come out of a cold basement or a hot car? Both the Garmin 500 and the 510 use barometric altimeters, and these are generally quite reliable - however, they can also be very temperature sensitive. Barometric altimeters usually have some type of temperature compensation, but if there is a sudden change in ambient temperature there can be some amount of drift in the readings while the unit stabilizes.

Had you noticed any difference in the beginning and ending altitudes recorded by the two units? Deviations and climb/descent measurements usually track with variation in the start/finish altitudes.

[eddief]

If you are primarily concerned with total gain at the end of a ride, would it make any difference what elevation the Gamin "thinks" you started at? It would maybe not be accurate to say what elevation you were at any point in the ride...but isn't total accumulated gain the same no matter where you start?

[Mark McM]

Related question - I often ride with Strava running on my phone (moto X) AND my Garmin running, and as you would expect, they finish with different numbers. But does anyone know which of the two might be MORE accurate? Which do you trust more - phones or garmins?

The Strava application on the phone gets it altitude information from topographic map information, whereas the Garmin gets its data from a barometric sensor. For absolute accuracy (when standing on surface of the earth) I'd expect the topographic map to be more accurate. But the Garmin can sense localized altitude changes that Strava can't - such as dips and rises in the road, or bridges or overpasses. While Strave might be more accurate for flattish terrain, or for large climbs/descents, but for rolling/uneven terrain the Garmin might come up with a number more reflective of actual altitude changes.

[Gfi3]

I have had similar issues with my Edge 800. I always end up with more elevation gain then my riding partners using their iPhones or Timex GPS. This past weekend it was roughly 600' over only 42 miles.

I will try turning the device on for a bit prior to starting the ride and see if that helps.

[russ46]

I have set the elevation points for 3 locations I frequently start rides from. This helps but I can still have problems in the summer when many of the roads I ride are heavily shaded. When I magnify the Strava map after a ride, I frequently see GPS drift that has me riding 50' or more above or below the road.

[2LeftCleats]

Neither of the units had been in extreme conditions: both came out of the same level of the same house.

I probably need to look at the directions again. I actually had no idea one could set the altitude.

Someone above asked what I wondered: though the absolute reading of individual points along the course might be skewed by a bad starting altitude number, wouldn't the total accumulated climb still be ok?

[Mark McM]

Someone above asked what I wondered: though the absolute reading of individual points along the course might be skewed by a bad starting altitude number, wouldn't the total accumulated climb still be ok?

It will have a small affect, but probably not enough to worry about. The relationship between pressure and altitude is not perfectly linear, but is close enough over the range of altitudes one typically rides. With an error in the starting altitude of a few hundred feet, the relative changes used for calculating climb/descent will be effected very little.

http://upload.wikimedia.org/wikipedia/commons/8/88/Atmospheric_Pressure_vs._Altitude.png

[kppolich]

Have you tried cleaning out the barometer opening on the unit? My 500 had a tiny hole that could get plugged and alter the elevation results. Pretty sure I have watched a youtube video on the cleaning of it somewhere here.

[Bob Ross]

Barometric altimeters are pretty accurate. The GPS one are wildly inaccurate.

I've heard ^^^this repeated numerous times before, and while I don't have any objective data to confirm it, I do know that when I go on rides where the elevation shown on my wife's Polar 'puter (which uses a baromateric altimeter) differs with the multiple GPS units that show up on the ride, my legs always feel like the Polar's results were more accurate!
:banana:

[josephr]

I take it with a grain of salt --- there's a tandem couple who both use their own Gamins and she's always .2-.3mph faster and he's always 100-200 ft more in climbing --- and they're both synced to the same speed sensor with identical settings.
Joe

[Mark McM]

I've heard ^^^this repeated numerous times before, and while I don't have any objective data to confirm it, I do know that when I go on rides where the elevation shown on my wife's Polar 'puter (which uses a baromateric altimeter) differs with the multiple GPS units that show up on the ride, my legs always feel like the Polar's results were more accurate!
:banana:

Well, not all GPS receivers are the same. Some WAAS enabled receivers can provide enough vertical accuracy for airplane landing glide slopes during instrument landing approaches (if enough satellites are in view). But these aren't cheap, and your typical cycling GPS is unlikely to have these capabilities.

Instead, cycling computers use the less expensive barometric altimeters, which can be perfectly adequate for most cycling needs.

[NickR]

Road with a friend yesterday and road the whole ride together taking turns pacing each other. He recorded is ride with Strava app and me with my Garmin. his stats 8,000 K and my 6,500 K so i went with is elevation gain lol.