Who to believe?

wellbeloved747

Did a 48km ride this afternoon in the crappy weather, i used my new Edge and had Strava running at the same time, they were started and stopped at the same time but the results vary quite a bit!!

Strava on the iPhone 5, in a waterproof case in the centre jersey pocket.

DISTANCE=47.2KM
MOVING TIME=2:02:40
ELEVATION GAIN=376M
CALORIES=1008
MAX ELEVATION=149M


Garmin edge 200, mounted with the included mounting kit, on the handle bars to the right hand side of the stem.

DISTANCE=46.67KM
MOVING TIME=1:48:38
ELEVATION GAIN=262M
CALORIES=1949
MAX ELEVATION=152M

These results are very contrasting, although the Garmin has done less distance and moving time it claims to have done about double the calories?

who should i believe?

Grill

Garmin for everything but the caloric algorithm (which are all rubbish btw).

wellbeloved747

i presume to get a proper reading i need a hr monitor?

imposter2.0

wellbeloved747 wrote:

i presume to get a proper reading i need a hr monitor?

HRM is useless for anything other than HR.

cougie

Altitude on these things are bobbins.
Calories are bobbins.
Distance is almost the same.
Time - you probably had auto start stop on the garmin.

The max elevation is almost the same.

simon_masterson

If the Garmin has an actual sensor on your wheel, then that.

wellbeloved747

Nope the Garmin is gps doesn't support wheel cadence, i did have auto stop on but then i thought Strava did? surely because there gps then altitude should be accurate, but i still cant get over the calories because the Garmin is double Strava!

simon_masterson

Oh dear.

Grill

You have a Venge and a Shiv but didn't think to get the 500? Seems bad...

vortice

Pretty obvious, but you have Strava and Garmin set up with you correct weight and age?

chrisaonabike

Are your two results both from Strava, having uploaded both, or is one from Garmin Connect?

I did a similar comparison yesterday, using my SGS3 with Strava recording the ride, and the Edge 800 recording, and then uploading the latter to Strava and Garmin Connect as well.

FWIW, my results were fairly consistent:

Edge (Strava) - SGS3 (Strava) - Garmin Connect
Moving Average: 14.9 - 15.0 - 15.1 mph
Distance: 29.1 - 29.2 - 29.1 miles
Calories: 940, 909, 876
Elapsed time: 1:59:12 - 2:00:07 - 1:59:11

bigpikle

The calorie numbers through these devices and software are just guesses - they might as well be blind guesses in all honesty. HR wont help either as you need to know exactly how much work (in kj) you actually did (and to do that you need a power meter) and then you need to know your own unique efficiency eg how many calories do YOU burn per kj of effort expended. Most people get a pretty good estimate of calories burned by simply kj=cals but its still a slight overestimate for many people.

The algorithm used in Polar devices is supposed to be the closest but it is not licensed to anyone else, and Garmins numbers are known to be particularly inaccurate.

Just ignore them and focus on something important...

ShutUpLegs

I'd trust a phone recording device to only get the distance right. Just

Bozman

Just compared my Garmin 500 to Cyclemeter on my iPhone, the difference over 51.5 miles - distance .05 variation, acsent - 7' over 3300' variation and the average speed was 0.02 mph different. The only major difference were calories burnt.

Pross

From what I've read on here iPhones aren't great at accurate GPS recording (not sure if it applies with a 5 though). I'd use the device designed specifically for the job but ignore altitude and calories, even with HRM fitted calories is a bit of guesswork - you need power to accurately calculate - and altitude works off barometric pressure.

de_sisti

With my Suunto T6c I get different hr readings (not by much) and calories expended (big difference)
when I download to Suunto Training Manager 2.3.0 and Suunto Movescount.

(edit; TBH, it doesn't bother me at all, it's just that I thought that the two Suunto interfaces interpret
what they read from the device differently).

simon_masterson

Get a wired computer, and buy some fancy shorts with the change.

pride4ever

Strava runs exactly with my computer in terms of distance and thats with it running on Android so....Believe your legs I guess. In terms of calories I dont worry about how many of them I burn on a ride as I'm pretty much see-through as it is lol.

smoggysteve

Surely the only two things that matter is time and distance. And you could work that out with a stopwatch and a map if you really need to know accurately. If elevation is important, the map can give you that info better anyway. Lot of time goes into making maps in the UK so they are pretty accurate.

Garry H

Pross wrote:

From what I've read on here iPhones aren't great at accurate GPS recording (not sure if it applies with a 5 though). I'd use the device designed specifically for the job but ignore altitude and calories, even with HRM fitted calories is a bit of guesswork - you need power to accurately calculate - and altitude works off barometric pressure.

Altitude on the gps unit doesn't work off barometric pressure. It should be reasonably accurate.

thefd

I would use use one and run with that. Probably the Garmin. It is a dedicated device for the stuff whereas the iPhone isn't.

On a side - if the wheel size is set correctly then the speed sensor will be more accurate than the GPS. Think of the times it loses signal and this will mess the whole ride, as it tries to find itself again.

cerv52

I usually upload my Garmin 500 to both Strava and Garmin connect and the only major difference comes in the calories burnt. The other readings are usually very close.

If your aiming to burn a certain amount of calories to help with weight loss just use the same service everytime to keep things consistent although not accurate.

butcher of bakersfield

I upload everything to Strava from my Garmin and Strava always plays everything down, in particular top speeds are always a couple mph slower. Distance is usually pretty much the same though.

pdw

Garry H wrote:

Altitude on the gps unit doesn't work off barometric pressure. It should be reasonably accurate.

GPS altitude is pretty inaccurate compared to horizontal positioning, yet as cyclists we're much more sensitive to altitude as a typical cycle might be 100km distance but only include 1km of climbing. This is why the higher end Garmins all have barometric altimeters.

tomisitt

I would go with the Garmin...a dedicated device made by a company that has been making GPS units for decades. I don't know the tech specs of the iPhone GPS, but the Garmins are 12-channel units which generally give very good accuracy. I'm guessing whatever system is in the iPhone is pretty basic compared to the Garmin.

Another plus with the Garmin is that on Garmin Connect there is an Elevation Correction option, which compares altitude info from the GPS unit with known altitudes from your route on the map, and then adjusts accordingly. As said elsewhere, the calories burned function is pretty basic, but at least gives you comparable data from the same device.

I don't have a lot of faith in the iPhone as anything other than basic GPS, and I have even less faith in Strava, but that's because I think Strava is a bit shit.

charlie_potatoes

tomisitt wrote:

I would go with the Garmin...a dedicated device made by a company that has been making GPS units for decades. I don't know the tech specs of the iPhone GPS, but the Garmins are 12-channel units which generally give very good accuracy. I'm guessing whatever system is in the iPhone is pretty basic compared to the Garmin.

Another plus with the Garmin is that on Garmin Connect there is an Elevation Correction option, which compares altitude info from the GPS unit with known altitudes from your route on the map, and then adjusts accordingly. As said elsewhere, the calories burned function is pretty basic, but at least gives you comparable data from the same device.

I don't have a lot of faith in the iPhone as anything other than basic GPS, and I have even less faith in Strava, but that's because I think Strava is a bit shoot.

Strava also has an Elevation Correction option.

Garry H

pdw wrote:

Garry H wrote:

Altitude on the gps unit doesn't work off barometric pressure. It should be reasonably accurate.

GPS altitude is pretty inaccurate compared to horizontal positioning, yet as cyclists we're much more sensitive to altitude as a typical cycle might be 100km distance but only includegures 1km of climbing. This is why the higher end Garmins all have barometric altimeters.

Not sure if the difference in accuracy between the two is as great in the UK, more so in the Alps perhaps. Academic in this case anyway; he can always upload the info into garmin connect and get a much more accurate reading based on known elevation figures.

charlie_potatoes

Garry H wrote:

pdw wrote:

Garry H wrote:

Altitude on the gps unit doesn't work off barometric pressure. It should be reasonably accurate.

GPS altitude is pretty inaccurate compared to horizontal positioning, yet as cyclists we're much more sensitive to altitude as a typical cycle might be 100km distance but only includegures 1km of climbing. This is why the higher end Garmins all have barometric altimeters.

Not sure if the difference in accuracy between the two is as great in the UK, more so in the Alps perhaps. Academic in this case anyway; he can always upload the info into garmin connect and get a much more accurate reading based on known elevation figures.

Strava also has an Elevation Correction option

Garry H

Charlie Potatoes wrote:

Garry H wrote:

pdw wrote:

Garry H wrote:

Altitude on the gps unit doesn't work off barometric pressure. It should be reasonably accurate.

GPS altitude is pretty inaccurate compared to horizontal positioning, yet as cyclists we're much more sensitive to altitude as a typical cycle might be 100km distance but only includegures 1km of climbing. This is why the higher end Garmins all have barometric altimeters.

Not sure if the difference in accuracy between the two is as great in the UK, more so in the Alps perhaps. Academic in this case anyway; he can always upload the info into garmin connect and get a much more accurate reading based on known elevation figures.

Strava also has an Elevation Correction option

they should both be bang on then. So i don't see what the problem is.

Gizmodo

Distance - to quote from Strava's Customer Support page: "Unfortunately, there are a few ways to gather distance data on a bike (or run) and each method of gathering the data can and may introduce some inaccuracy."

GPS data is not always accurate, as Garmin say "Garmin® GPS receivers are accurate to within 15 meters on average."

Elevation data with GPS is even worse, again to quote Garmin "It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft." And Strava say "Since elevation data derived from a GPS signal is fairly inaccurate, Strava automatically corrects elevation derived from a GPS source by consulting elevation databases to determine the elevation at each point in the activity."

Finally Calories, Strava say: "Calorie calculations are only estimates. You may notice differences between Strava's calculations and those from other tools, even given the same activity data. This is most likely due to differences in Calorie calculation algorithms, and the data factored into the calculations. We believe our estimation is as accurate as possible given the limitations in data."

So in sumary, if you took an average of both lots of data, you would probably be close to actual. These devices are "consumer grade" and not commercial so are never going to give pin-point accuracy. You need to use the data as a guide, not gospel. If you want greater accuracy for distance, get a computer with a wheel sensor, accurately measure the size of your wheel and enter that manually into the device.

kieranb

reminds me of looking at some gradient numbers for a hill near me, the road sign says 18%, mapped it using some online software like ridewithgps (and one or towo others) and it gave max gradient as 4%!. Having ridden up and down it a few times the council sign is nearer the mark.