Has anyone with a factory nav system noticed a difference between distance driven on the nav verses odometer? i was on the highway, set the cruise for 60 mph and hit the nav for home. when you press the left radio button then press the trip button, it shows average speed, distance driven and time driven. i first noticed that if you multiply your average speed with your time, it did not match distance. in fact it wasn't really even close. distance doesn't match the odometer either. has anyone else noticed this and does anyone know why? standard tires on factory wheels.