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Grade-adjusted pace comparison (Garmin vs Strava vs Runalyze): bug?

derek87
over 2 years ago

so, one of the new features on 13.15 is Grade adjusted pace. i am seeing a pretty big discrepancy between what Strava and Runalyze report. here are numbers from a run yesterday with laps every mile (last one is 0.17mi)

Non-adjusted: 9:27, 9:16, 9:25, 9:06, 8:56, 8:42, 8:45, 8:44, 8:24 (Ave: 8:58)

Garmin:          9:26, 9:28, 9:17, 9:07, 8:59, 8:40, 8:53, 8:41, 8:22 (Ave: 9:00)

Strava:           9:25, 9:21, 9:10, 9:00, 8:38, 8:40, 8:52, 8:22, 7:53 (Ave: 8:54)

Runalyze:      9:26, 9:23, 9:20, 9:06, 8:54, 8:41, 8:49, 8:35, 8:12 (Ave: 8:56)

i do notice that Runalyze, starting a few months ago, reports a smaller net elevation change than Garmin and Strava, which seems reflected in the smaller difference between raw and GAP.

however what surprises me is that the Garmin is reporting a average GAP taht is greater than the raw/non-adjusted pace which is a bit of a surprise to me as i would expect GAP to always be a little faster than the raw for a relatively flat loop course.

  • 0 over 2 years ago

    What is your elevation numbers for the loop? I can easily think GAP is faster if there is more descent than ascent.

    But for the GAP, it's like running power. I don't think there is any scientifically agreed formula for it.

  • 0 over 2 years ago in reply to jmto

    it's a complete loop so net elevation change is zero. Strava and Garmin report the ascent as 115ft, while Runalyze marks it as only 62ft total.

  • 0 over 2 years ago in reply to derek87

    Real elevation change is zero, but was is also in the numbers? As those don't usually exactly match, but are also usually pretty close, but the 0:02 difference is also pretty small so maybe the couple of meters more descent could explain it.

  • 0 over 2 years ago in reply to jmto

    yes, there were real changes between the "laps" most certainly the greatest elevation change (that is definitely felt while running) is over the last 2 miles of the run where there is a steady ascent for most of it. i feel the Garmin number is way off for mile 8. i would definitely feel like there is at least a 0:15-0:20 min/mi penalty for this stretch of the run due to the slight incline.

    but as you suggest, this is all an art and there is probably no definitive "Truth" for how to do it. 

  • 0 over 2 years ago

    There's a German running coach (Greif) that has his own GAP calculator. In short: running 1 km with 1 m elevation gain is about equal to 1006 m without elevation, 1 m elevation drop is equal to 998 m. 

    Years ago I compared it to Strava. I think Greif is weighing elevation changes higher and is (according to my feeling) closer to reality.