Which Elevation To Believe?
11-04-18, 05:47 PM
#1
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Which Elevation To Believe?
This afternoon mapped out a 35 mile route for my Gaemin 1030. The route said 1,500ft. of elevation. My actual ride says just under 2,800. That's close to 100% inaccurate. Which figure is the most accurate?
11-04-18, 06:05 PM
#2
Non omnino gravis
Man, I wish I had a GPS unit that would overstate elevation gain. I've never had a route come out to a bigger gain that what was stated in the pre-ride routing. Ever.
But a 2,800ft gain over 35 miles would be climbing a mountain. If you didn't spend around half your time going up 6-7% grades, it's unlikely you did 2,800ft.
But a 2,800ft gain over 35 miles would be climbing a mountain. If you didn't spend around half your time going up 6-7% grades, it's unlikely you did 2,800ft.
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11-04-18, 08:49 PM
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According to Garmin, the following can affect the elevation data on a 1030:
“What are some of the factors that can cause an elevation reading to be wrong?
I’ve no clue why the unit mounting location, nor the riding solo vs, group ride, would affect the data, but that’s the official Garmin explanation. Obviously weather and temperature will affect the barometric sensor where as the actual GPS elevation data will be all over the place, cause GPS receivers in general, are notoriously inaccurate at determine elevation.
Thus I’d say the unit is totally in error.
If you want a better sense of what the on-line route creation data is stating, run the route thru different programs, RWGPS, Connect and Strava, as example. I’ve seen differences between RWGPS and Connect, but only 60-70 ft. In 3500 or so and I chalk that up up how the particular program reads the map data.
“What are some of the factors that can cause an elevation reading to be wrong?
- Where the device is mounted on the bike
- Garmin recommends the use of a Garmin mounting accessory placed near the handlebars of the bike
- Weather conditions
- Group vs. solo riding
- Road traffic
- Covering the device with stickers or a case. If you cover the barometric port on the device which is tiny hole generally found on the back or sides of the device this will negatively affect elevation accuracy.
I’ve no clue why the unit mounting location, nor the riding solo vs, group ride, would affect the data, but that’s the official Garmin explanation. Obviously weather and temperature will affect the barometric sensor where as the actual GPS elevation data will be all over the place, cause GPS receivers in general, are notoriously inaccurate at determine elevation.
Thus I’d say the unit is totally in error.
If you want a better sense of what the on-line route creation data is stating, run the route thru different programs, RWGPS, Connect and Strava, as example. I’ve seen differences between RWGPS and Connect, but only 60-70 ft. In 3500 or so and I chalk that up up how the particular program reads the map data.
11-04-18, 08:59 PM
#4
Non omnino gravis
A fun one is after a ride, go to the Strava activity page, click the little wrench and choose "create route." I'll do a ride and the Garmin will report say 1,200ft. I'll go to Create Route and it will be ~1,500ft. I'll look at the upload from my wife's Garmin 500, and it will be 1,470ft.
I had one single ride where the 520 over-reported elevation. I got caught in a downpour, the quarter-turn mount filled with water, and my elevation suddenly rocketed up 1,000ft.
I had one single ride where the 520 over-reported elevation. I got caught in a downpour, the quarter-turn mount filled with water, and my elevation suddenly rocketed up 1,000ft.
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11-05-18, 08:42 AM
#7
Senior Member
My Wahoo Elemnt routinely reports 10-25% less elevation than the Strava corrected. I do loop rides and the start and end elevation are often different.
On the flip side, when using my speed sensor the Elemnt final distance is roughly 1-5% higher than Strava corrected. I measured my tires rotation with chalk and like 5 rotations and my circumference is consistent with the charts. When using the Elemnt GPS speed/distance and not the speed sensor, it is ±1% and very close to Strava corrected.
I usually just let Strava correct it so I at least have some consistency over time.
On the flip side, when using my speed sensor the Elemnt final distance is roughly 1-5% higher than Strava corrected. I measured my tires rotation with chalk and like 5 rotations and my circumference is consistent with the charts. When using the Elemnt GPS speed/distance and not the speed sensor, it is ±1% and very close to Strava corrected.
I usually just let Strava correct it so I at least have some consistency over time.
Last edited by u235; 11-05-18 at 09:04 AM.
11-05-18, 09:46 AM
#8
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My Wahoo Elemnt routinely reports 10-25% less elevation than the Strava corrected. I do loop rides and the start and end elevation are often different.
On the flip side, when using my speed sensor the Elemnt final distance is roughly 1-5% higher than Strava corrected. I measured my tires rotation with chalk and like 5 rotations and my circumference is consistent with the charts. When using the Elemnt GPS speed/distance and not the speed sensor, it is ±1% and very close to Strava corrected.
I usually just let Strava correct it so I at least have some consistency over time.
On the flip side, when using my speed sensor the Elemnt final distance is roughly 1-5% higher than Strava corrected. I measured my tires rotation with chalk and like 5 rotations and my circumference is consistent with the charts. When using the Elemnt GPS speed/distance and not the speed sensor, it is ±1% and very close to Strava corrected.
I usually just let Strava correct it so I at least have some consistency over time.
Five different websites roughly agree with what I see on my Polar but Strava subtracts 2% to 4% distance and adds 20% to 40% elevation to them all.
11-05-18, 10:25 AM
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IIRC there's a setting buried in the web interface for my Garmin 800 that lets me select the barometric (on-device) elevation gain over the on-line mapped gain. Are you using the barometric data? It's possible, depending on the route, that the on-line will miss the fact that a road goes through a cut or over a fill, and credit you with climbing all sorts of contour lines.
11-05-18, 01:08 PM
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Occasionally a GPS will add a point in a track that has an erratic (false) location, but if that occurred your distance should have been off too. If you plotted up the data, did you see an odd peak or valley show up in the plot where there was no such land feature?
11-05-18, 01:29 PM
#11
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Occasionally a GPS will add a point in a track that has an erratic (false) location, but if that occurred your distance should have been off too. If you plotted up the data, did you see an odd peak or valley show up in the plot where there was no such land feature?
Here is an Strava's explanation
I'm no KOM chaser but I do like to compare some of my own times on some sements. There are rides where Strava is missing a segment I did on a ride. There was some obvious GPS issues on my Elemnt and Strava didn't have a good enough stream to see I did that segment. The map shows me there but I guess just not accurate enough.
Last edited by u235; 11-05-18 at 01:35 PM.
11-05-18, 02:32 PM
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Getting a good estimate of elevation is not trivial. Uncorrected GPS-based altitudes used by mapping platforms are thrown off by bridges/overpasses, where terrain and road are on different planes.
From what I understand, bike computers will report altitude based on either barometric sensor (more accurate according to Garmin) or GPS (reportedly accurate at +/- 15 feet). Note that a fairly accurate GPS measurement could result in inflated "total elevation" if readings fluctuate, which is less likely with a barometer.
So... If by route you meant elevation computed by the mapping app, I'd bet that there are bridges.
From what I understand, bike computers will report altitude based on either barometric sensor (more accurate according to Garmin) or GPS (reportedly accurate at +/- 15 feet). Note that a fairly accurate GPS measurement could result in inflated "total elevation" if readings fluctuate, which is less likely with a barometer.
So... If by route you meant elevation computed by the mapping app, I'd bet that there are bridges.
11-05-18, 03:54 PM
#14
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I'm sorry but Strava is just wrong, as in completely whacked out.
Polar GPS: 1115 ft.
Polar Flow Website: 1115 ft
Training Peaks: 1115 ft
Ride with GPS: 1125 ft
Strava: 1824 ft
I didn't ride over 800+ ft of bridges. Stava doesn't know what to do with Polar altitude data.
Polar GPS: 1115 ft.
Polar Flow Website: 1115 ft
Training Peaks: 1115 ft
Ride with GPS: 1125 ft
Strava: 1824 ft
I didn't ride over 800+ ft of bridges. Stava doesn't know what to do with Polar altitude data.
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