Sporttracks/Garmin Training Center inconsistencies

[davidB]

looking at the same ride in both programs i get different results in just about every category.

biggest example: Sporttracks says my fastest speed was 23.4, while Garmin Training Center says 35.5. Garmin appears to be right in this case.

most of the other main categories seem to be off by a little amount as well. (time, distance, ascent/descent)

so what gives?

[ericfoltz]

Each program has it's own formulas for taking the raw data from the unit and converting them to stats.

Seeing as Garmin makes the unit, I tend to trust the stats from Training Center more than those from other programs.

[kanga]

Just a hunch that I have to confirm, but I believe sport tracks only looks at track point data. It calculates the distance and elevation change and the time change between the track points and cumulates that for the totals.

The Garmin units record track points and also records the distance/elevation change between the track points, and uses recorded distance, not the "as the crow flies" calculated distance between trackpoints to come up with the totals.

My sport tracks distances are also slightly lower than the GTC distances, and more so if it's a tight, switchbacked trail. On road rides the difference is less, which is what led me to this theory.

I'm sure someone out there knows the real answer, and I'd love to know too.

[Abui]

Originally Posted by davidB

looking at the same ride in both programs i get different results in just about every category.

biggest example: Sporttracks says my fastest speed was 23.4, while Garmin Training Center says 35.5. Garmin appears to be right in this case.

most of the other main categories seem to be off by a little amount as well. (time, distance, ascent/descent)

so what gives?

Your GPS is continually computing your speed during the ride. It can report the maximum speed as an item separate from all the GPS data points. Garmin SW may be smart enough to use that.

Sporttracks may be reporting the speed as computed between each GPS point. So what is the time interval between each point? Your GPS can record the data in 1 second intervals or much more than 1 second in smart recording mode.

edit: agreeing with Kanga

[Burner]

having only put 2 rides from my 705 into Training Center and SportTracks, the most glaring difference I noticed was with ascent/descent (they were both 1000' less in Sport Tracks)

[bcblur]

Check your smoothing values in SportTracks. These values can significantly change the calculated values like elevation change and speed. I keep my smoothing values nice and low for cycling. If I were using SportTracks for running, I'd probably have them higher.