Strava underestimate my avg speed and overestimate travel when using cycle computer

[igoruss]

Hello, can someone explain me why strava is messing with my routes uploaded from cycle computer? 

1. I'm recording my routes (commuting in a big city ) with my gps bike computer (iGPSsport BSC100S) with a speed sensor on a wheel. It has an app where I can see the results via bluetooth. For example todays route I drove: 12,2km, 30:40 moving time, avg speed 24kmh

2. Computer's app is linked to strava and it automatically uploads route to strava when I save

3. That exact same route on Strava has 20% worse results: 12,1km, 35:03 moving time, avg speed 20,8kmh.

I tried manually export .gpx, .fit and .tcx to strava and each file extension has different results! .tcx are total mess, it tells me that I was driving 85kmh  (vmax) and shows 29min time.

Speed sensor are calibrated with gps reading and correct wheel size

[Jane · Accepted solution]

Hello @igoruss 

Thanks for posting about this and sorry to hear you're seeing some irregularities with the moving time shown in your Strava activities.  

For cycling activities, we use the recorded GPS data to calculate your moving time.   Strava relies on a speed threshold to determine whether or not you are resting. Your device or platform may use a different method than Strava when calculating your stats, which can result in some discrepancy between the moving time shown on your device and the moving time shown on Strava.  If the discrepancy is large, it's could be due to gaps or anomalies in your GPS data.  More information here

Let me know if that's helpful.