So last night a TT recorded 246w average on my garmin via a powermeter, uploaded to Strava as 236w.

Today, an outdoor ride at 226w & 29.9kmph on the garmin uploads as 213w 28.9kmph.

Why’s it wrong?

It’s about 3% difference. Both would probably have some form of accuracy tolerance and considering you’re relying on things a long way away to pinpoint your position I wouldn’t think 3% would be too bad?

you wouldn’t be complaining if Strava was 10watts higher each time 🙂

Too right I wouldn’t 😀

It’s about 3% difference. Both would probably have some form of accuracy tolerance and considering you’re relying on things a long way away to pinpoint your position I wouldn’t think 3% would be too bad?

But Strava isn’t measuring power, it’s merely taking the XML from the Garmin’s recorded data. I can only imagine it’s not taking all of the data points. I’ve noticed the same.

have Strava/GPS fun when riding with others and see how different your distance and altitude gains are.

What Stevied said, if each system (power, GPS) as a +/-2% error then you could end up 4% out.

You get massive variances in altitude too, last night my garmin recorded 669m and my S6 579m on the same route

Yes, but Kryton57 isn’t using 2 different GPS devices – it’s the same one.

Yes, but Kryton57 isn’t using 2 different GPS devices – it’s the same one.

It’s the same dataset being interpreted by two different web interfaces. I’ve noticed Strava generally seems to be lower than Garmin for averages, it must work them out slightly differently.

It’s not “wrong” as such both use different algorithms to interpret the data.
Lots of info about this on the strava forums etc

Just for the record the Garmin numbers are being read of the device pre-upload, not Garmin Connect.

I guess its in my favor should any competitors underestimate my massive power potential… 😳