Strava GPS tracking differences Garmin 520 vs 230

ajmitchell

I would be interested in anyone's opinion on this. I attached two computers to the bike Garmin 520 and Garmin 230. 230 is a fitness watch with GPS. Both should have glonass GPS which garmin says is accurate to 3meters. I would have thought two Garmin units, both current, both attached to the bike would read almost exactly the same. However in a short 10km ride, they are out of sync upto 3 seconds (sometimes up and sometimes down). OK this is modest and you might think this makes no difference but on one segment I was award 12th place on strava on the Garmin 520 and 3rd on the Garmin 230!

Here is a comparison of the data between the two

Any comments? On most social rides it will make little difference between on a KoM hunt or going after a PB is might. Anyone seen this before?

dinyull

So basically, instead of buying a new aero frame, helmet, kit etc I can just but a 230 and save 3 seconds per 10km.

Sorted.

Pulsatingstar

If you have them both set to 1 second recording rather than smart, that could account for 1 second of the error as well as the error in where it actually takes the GPS position you noted. Youd have needed to set them at 1 sec too as I think smart is the default.

wongataa

ajmitchell wrote:

Any comments? On most social rides it will make little difference between on a KoM hunt or going after a PB is might. Anyone seen this before?

It will be a combination of different GPS sampling rates and Strava's slightly dodgy way it works out segment times.
For the best accuracy you need to set your devices to log every second. Strava doesn't interpolate between position data in the GPS logs and as a consequence the length of the segment will vary on how close the nearest recorded position points are in relation the the actual end points. This is why you can sometimes see hilarious speeds for some segments and why short segments are really problematic. The longer the segment the less of an issue it is.

ajmitchell

thanks all, I didnt know about gps sampling, I have just checked and both devices were on smart mode. I'll swap them to 1sec and see if that makes any difference.