Merging ride data from GPX file

[flysplat]

After each ride I usually download the GPX file from Strava and merge it with the Ibike file so that I have a map of the route in Isaac.

Each time I do the merge I see a window titled File Syncronisation Result and it then shows 2 graphs of speed data.

There is always an area where the Ibike speed and Topografic GPX are widely different.

I've attached a screenshot to illustrate the point. This happens on all rides but at different points in the ride.

Can you tell me what it's telling me please?

[Velocomp]

Your Garmin and your PP both record speed data. The question is: WHEN do they start to record that data. Your PP starts recording data when you start riding. Your Garmin starts recording when you press the "start" button. Since these two event almost never happen at precisely the same time, when the ride files from PP and Garmin are merged, there will be some misalignment between Garmin speed data and PP speed data. The top graph shows the data as it is recorded; the bottom graph shows the data as re-aligned by Isaac.