New to garmen 830 with speed sensor. Avg speed on garmen during ride is lower that syced data to strava which is faster avg speed. also the history on garmen shows lower mileage and avg speed that data syced to strava.

Check the Auto Pause setting on the Edge 830. If Auto Pause is off, then the timer will continue to run when you stop. So the average speed is the distance traveled divided by the total elapsed time. If Auto Pause is on the Average speed is the total distance divided by the elapsed time minus the stopped time. Strava uses elapsed time minus stopped time. 

So if Auto Pause is off your average speed on the Edge 830 will be lower than the average speed on Strava because it includes stopped time.

owenpga Does the information displayed on your 830 match what is uploaded to Garmin Connect? There is potential for Strava to do their own processing, so I would be curious if your Garmin Connect account reflects what you see on your device. 

Numbers seem to be correct now. Changed it to auto pause . thank you 

thank you 

You're welcome.  It takes a while to learn how these things work.