Strange thing happened to me the other day. I was riding with my wife, we both run Strava, on our normal 20 mile loop. We always end up at 20 miles on Strava on this loop, so this was very strange to me. She ended up at 20 miles like normal at a 13.9 mph pace (slow day). My Strava showed 18.8 miles at a 15.2 mph average. The Strava map indicates the same exact turn around point and even grouped us together, but there was still the massive discrepancy. I say its on the fritz!