Speedometer error?
 

I was curious, I was following my wife in her car one day and she was at 55 and my speedometer read 63, then a few weeks later, I passed one of those speed displays they usually post as you go into a road construction site and I was doing 70 but the display read 60. On my Android phone, I have an app called speed view. I was actually measuring distance with it, but it has a feature the shows the max speed. At one point I was doing about 85, but the max speed on the app was 70.

I went out on the interstate and opened her up. My speedometer read 120, but the max speed on the app said I was only doing 101.

So what's going on? I know the rear sprocket is the stock sprocket, not sure about the front one. What could be causing such a drastic difference in speeds between my speedometer and the car, radar and the app n my phone?

Motorcycle speedometers are notorious liars. That's why speedo-healers are popular.