Strava "v" Garmin. Quite differing readings. Why?

Fatamorgana

I have both "systems" working on any given ride and they give quite different results. This is my local 2hr training ride in NE Herts / Essex.
http://www.strava.com/activities/209661021

Anyhow, Strava gives the first number, Garmin* the second on the same, 'round trip.

35.7 - 35.6 miles
17.3 - 17.7 av speed
1408 - 2233 calories (not that I care)
1716 - 2129 ft of climbing
41.2 - 37 mph top speed
2:04 - 2:00 hrs riding

Any thought why such discrepencies?

*2014 Garmin Edge Touring, not that it would make an difference, surely.

norvernrob

Strava tends to reduce elevation, Garmins tend to over-egg it slightly, at least my 200 usually does. The top speeds on strava seem to be plucked out of thin air. The calories for both are just calculations (guesses) so will not be accurate. The auto stop on Strava is iffy at best and will always give you more moving time than a Garmin with auto stop set.

Dippydog3

When you say "both systems" what do you mean?

You record on your Garmin. Do you record on anything else?
Where is the data you refer to coming from? Which websites? Uploaded how?

Fatamorgana

The Strava is recorded on my phone.
The Garmin has very detailed maps on the UK pre-loaded, and can provide masses of location data accordingly. Thus I am tempted to believe the Garmin.

Both use GPS satellites, maybe not all GPS satellite information is equal - how very Orwellian, rather apt since he wrote Animal Farm in the next village to where I live.

The data is coming from Strava's web portal - I provided a link and the Garmin info / ride data is from the physical unit.

Calorie count is no doubt based on different models and are thus subject to other, in-put criteria such as height, age, weight; not so the moving ride data, you'd have thought.

norvernrob

Fatamorgana wrote:

The Strava is recorded on my phone.
The Garmin has very detailed maps on the UK pre-loaded, and can be provide masses of location data accordingly. Thus I am tempted to believe the Garmin.

Both use GPS satellites, maybe not all GPS satellite information is not equal!

The data coming from, and the last two questions make no sense, so please explain what you are asking. I provided a link and the Strava info / ride data and the Garmin data is from the physical unit and their website were I to upload each ride (which I do not).

Calorie count is no doubt based on different models and are thus subject to other, in-put criteria such as height, age, weight; not so the moving ride data, you'd have thought.

The GPS data they receive is the same barring the odd section under trees etc when they can differ if one received the signal better than the other. The discrepancies in the speed/time are pretty much all down to the Garmin auto stopping but Strava app doesn't perform the task as well. The elevation data is calculated differently which is why that differs.

Fatamorgana

The Garmin goes into "Pause mode" below about 2mph, so that is not a factor in this equation I'd suggest.

The difference in elevation is the most strange, we're talking about over 400ft with the same Start and Finish Point, it being a circuit.

Buckie2k5

use your garmin for strava too, keep your phone for phoning

Fatamorgana

Sounds like the Strava software is the least accurate, and besides, I have no one who calls me nor texts me, having no mates, unless you count the bank and Vodaphone.

norvernrob

Fatamorgana wrote:

The Garmin goes into "Pause mode" below about 2mph, so that is not a factor in this equation I'd suggest.

The difference in elevation is the most strange, we're talking about over 400ft with the same Start and Finish Point, it being a circuit.

Of course it is. Your Garmin is pausing and strava isn't, which is why it has given you 4 minutes more ride time and a slower average speed.

From my experience with running both at once, Strava tends to under-read elevation by 10-20% and Garmins often over-read by as much as 10%. However, the longer and hillier the ride the closer together the results seem to be (sounds strange but it's true, I followed the route of the Peaks Epic which has 7300ft of climbing, my Garmin said 7300ft and Strava app said 7264ft. It's been similar with other long hilly rides too)

Fatamorgana

Strava has a Pause facility, but clearly, not quite as sensitive as on reflection, with T junctions and a pee, I think we can safely account for the three & a half minutes that I was stationary.

You'd have thought that the % error across these figures would also apply regardless of the time or distance.

Bozman

Fatamorgana wrote:

The Garmin goes into "Pause mode" below about 2mph, so that is not a factor in this equation I'd suggest.

The difference in elevation is the most strange, we're talking about over 400ft with the same Start and Finish Point, it being a circuit.

I've seen somewhere around 800' difference on a 50 mile ride, a Garmin 500 was showing X and when it was downloaded to Strava it showed 800' less, 3 Garmins on the ride and wildly different ascent readings on Strava and the 800 showed more ascent than the 500s on connect.

There's a recent post that goes into detail about GPS....failings.

mitchgixer6

I've been testing this recently too after buying a 500 and find the Garmin to both under read distance and time, but as already mentioned I think this must just be down to the auto pause function.

There's an option on Garmin Connect to 'correct' the elevation which seems to bring the elevation trace much closer to the Strava reading. I think this will be the more accurate reading as the Garmin reads elevation from barometric pressure and Strava uses information gleaned from OS maps. When you use the elevation correction feature on Garmin Connect it uses the same method and disregards the barometric readings.

barrowmatt

I've seen strava record segment speeds faster than the ride max speed! I assumed it calculates segments based on the road map rather than just point to point, so if you hit all the apexes on a twisty descent you can get a ridiculous segment speed

jimothy78

mitchgixer6 wrote:

There's an option on Garmin Connect to 'correct' the elevation which seems to bring the elevation trace much closer to the Strava reading. I think this will be the more accurate reading as the Garmin reads elevation from barometric pressure and Strava uses information gleaned from OS maps.

It might make the two systems differ less from each other, but that doesn't necessarily make it more accurate. The reason strava underestimates the height differences is because the map data it looks up doesn't have enough fine detail, so every time you change from climbing to descending or vice-versa, a little bit gets clipped off. Imagine reading altitude off a series of contour lines on a map yourself - the distance between each is 10m, so by counting contour lines, each climb/descend measurement is +/- 5mm - this is probably why the errors are less obvious on longer, steeper rides - the margin of error on each rise/fall is the same, but it's a much lower percentage of the total figures. Add in the fact that these rides involving big hills are likely to be made up of fewer, but more extended rises and falls, so there are fewer peaks/troughs to incur such errors.

jimothy78

barrowmatt wrote:

I've seen strava record segment speeds faster than the ride max speed! I assumed it calculates segments based on the road map rather than just point to point, so if you hit all the apexes on a twisty descent you can get a ridiculous segment speed

It doesn't work quite like that - it doesn't refer to the "road map", as you put it, but the initial segment statistics it got from the user who created the segment. As long as your recording follows that route close enough for strava to match it up, your segment speed will be calculated against that distance. For instance there's one technical offroad descent near me that takes about 2 mins to ride, but the KOM is due to someone bombing down a nearby fireroad - a much shorter/faster route, but because strava (incorrectly) managed to match their spatial data to the segment, it calculates the speed (88km/h, apparently :roll:) against the original segment's distance.

drummer_boy

I find it worse than this. I feed my Garmin 800 into Sportstracks and Strava, and get different results from the same core data set!!
Amount of climb is the biggest variant.
The other issue is that me and the missus can do the same ride, and her Garmin 500 will register 0.5miles further (over 20 or so miles) and a few hundred feet more climb!!
It's all black magic and guesswork I tell you :-)

Dippydog3

Forget the science.

The one that is correct is the one has has you cycling the furthest, the fastest, or climbing the most.

Load both to Strava and delete the one that makes you look most wimpy.

Doesn't everyone do that?