Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!)

May 3, 24 9:34

Post #1 of 17 (971 views)

Can y'all help me understand why there's such a difference in AP results between all the different tracking tools I use (maybe I should just not use all 4, but that's a separate problem)? I get that all use different algo's for the "net power" but shouldn't AP be the same / close? Strangely, sometimes Strava is higher than Garmin, but mostly it's lower

From a 50min crit last night, here's what all 4 of those showed ...

Garmin:
AP 330
NP 381

TP
Power 330
NP 369

Strava
Power 318
Weighted Avg 341

Xert
Power 310
Equiv Power 380

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mvenneta] [ In reply to ]

May 3, 24 9:47

Post #2 of 17 (958 views)

Yup, Normalized Power is going to be different, because that concept is licensed so the formulas and different. For Average Power, that does not make sense they could be lower. I could see Strava being higher, if it automatically excludes stops. But being 12W lower (and 20W lower in Xert) is a mystery.

I'm pretty sure all my averages (between Garmin, Strava, and TrainerRoad) all match exactly or are within 1 watt.

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mvenneta] [ In reply to ]

May 3, 24 10:06

Post #3 of 17 (937 views)

What does the hear rate data show for each of the four interfaces?

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mvenneta] [ In reply to ]

May 3, 24 10:10

Post #4 of 17 (927 views)

Is your Garmin set to include zero values for power?

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [Yutaka Sonik] [ In reply to ]

May 3, 24 10:17

Post #5 of 17 (920 views)

Yutaka Sonik wrote:

What does the hear rate data show for each of the four interfaces?

HR is identical on all 4

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mhepp] [ In reply to ]

May 3, 24 10:21

Post #6 of 17 (913 views)

mhepp wrote:

Is your Garmin set to include zero values for power?

My garmin 840 is set to:
- Cadence Averaging - do not include Zeros
- Power Averaging - include Zeros

Is this right?

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mvenneta] [ In reply to ]

May 3, 24 10:27

Post #7 of 17 (897 views)

Just verifying, usually power on my Garmin appears 10w lower on Strava. For trainer rides (zwift/rouvy) Strava Matches up - I also record these indoor rides on garmin, also matching up. So I am guessing Strava' is doing something different

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [exxxviii] [ In reply to ]

May 3, 24 10:29

Post #8 of 17 (897 views)

exxxviii wrote:

Yup, Normalized Power is going to be different, because that concept is licensed so the formulas and different. For Average Power, that does not make sense they could be lower. I could see Strava being higher, if it automatically excludes stops. But being 12W lower (and 20W lower in Xert) is a mystery.

I'm pretty sure all my averages (between Garmin, Strava, and TrainerRoad) all match exactly or are within 1 watt.

I'd be curious if you checked, and could validate all are the same. I find that all 4 of them are NEVER the same

On a normal training ride the figures are usually close, but when we race (particularly crits), the figures are consistently wildly different

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mvenneta] [ In reply to ]

May 3, 24 10:39

Post #9 of 17 (888 views)

mvenneta wrote:

mhepp wrote:

Is your Garmin set to include zero values for power?

My garmin 840 is set to:
- Cadence Averaging - do not include Zeros
- Power Averaging - include Zeros

Is this right?

Whether it is right or not is up to you and how you use the data.

If you were not including zero power that could be a potential source of the difference. Wonder if the exclusion of zero cadence but not zero power is throwing things off - might be worth doing a ride including zero cadence to see if that changes anything?

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mvenneta] [ In reply to ]

May 3, 24 11:05

Post #10 of 17 (859 views)

Here are my last few indoor & outdoor rides:

60 mile outdoor: Garmin 183AP/191NP; Strava 183AP/185WAP
25 mile outdoor: Garmin 145AP/174NP; Strava 144AP/169WAP
21 mile outdoor: Garmin 143AP/151NP; Strava 143AP/147WAP
60 minute indoor: Garmin 189AP/195NP; Strava 187AP/192WAP; TrainerRoad 187AP/192NP
30 minute indoor: Garmin 228AP/249NP; Strava 226AP/242WAP; TrainerRoad 226AP; 246NP
90 minute indoor: Garmin 189AP/194NP; Strava 187AP/191WAP; TrainerRaod 187AP/192NP

mvenneta wrote:

My garmin 840 is set to:
- Cadence Averaging - do not include Zeros
- Power Averaging - include Zeros

Is this right?

Yes this is right.

Last edited by: exxxviii: May 3, 24 11:07

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [exxxviii] [ In reply to ]

May 3, 24 16:44

Post #11 of 17 (785 views)

Yours are way closer than mine

I rode on trainer (different PM, different bikes, no garmin) today and Strava was higher than TP. Makes no sense to me

Strava
AP 205
NP 212

Training peaks
AP 197
NP 217

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mvenneta] [ In reply to ]

May 4, 24 6:37

Post #12 of 17 (677 views)

Garmin: This is exactly what was recorded.

TP: This is exactly what was recorded and we invented NP so shut up.

Strava: According to your data, we think you suck.

Xert: We're doing our own thing and everyone else is wrong. Do it our way, do it our way, do it our way...

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [exxxviii] [ In reply to ]

May 4, 24 8:14

Post #13 of 17 (641 views)

exxxviii wrote:

Yup, Normalized Power is going to be different, because that concept is licensed so the formulas and different. For Average Power, that does not make sense they could be lower. I could see Strava being higher, if it automatically excludes stops. But being 12W lower (and 20W lower in Xert) is a mystery.

I'm pretty sure all my averages (between Garmin, Strava, and TrainerRoad) all match exactly or are within 1 watt.

NP is trademarked; the formulas aren't patented.

mvenneta wrote:

mhepp wrote:

Is your Garmin set to include zero values for power?

My garmin 840 is set to:
- Cadence Averaging - do not include Zeros
- Power Averaging - include Zeros

Is this right?

I'd add ensuring auto-pause is also off on the device. Strava generally has weird averaging for me, and diverges the more % of time I'm not moving during a ride (even though I have auto-pause off).

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [aravilare] [ In reply to ]

May 4, 24 10:29

Post #14 of 17 (608 views)

aravilare wrote:

NP is trademarked; the formulas aren't patented.

Garmin and TrainerRoad both use Normalized Power. So I would expect their formulas and results to match. Strava and Xert use their own concoctions: "Weighted Average Power" and "Xert Equivalent Power." So, I would not expect those two to match each other or Normalized Power.

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [aravilare] [ In reply to ]

May 4, 24 11:32

Post #15 of 17 (584 views)

There’s no auto pause .. and it’s a race so there’s no stoppage time

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mvenneta] [ In reply to ]

May 4, 24 13:06

Post #16 of 17 (542 views)

Have you checked that recording is set to every second, and not smart recording? This can be a source of errors.

Re: Power differences between Garmin, Strava, TrainingPeaks and Xert (oh my!) [mvenneta] [ In reply to ]

May 4, 24 20:49

Post #17 of 17 (458 views)

Just as another data point, I ride with a girl here who has Strava showing about 10W lower than on average on every ride. Garmin and TP match up. It's been going on for a few years and she rides every day.

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