GPS MPH accuracy

[kmf]

Which is more accurate: the car's speedometer or a GPS app? The GPS app would be Car Home Ultra (which features a MPH icon) or my 2007 Ford Explorer Limited (with 18" wheels.) The GPS mph is approx 4-5 miles slower than the Explorer's mph.

 

[Country_Gravy]

Go with whichever one might get you out of a speeding ticket.

 

[LaTuFu]

I would trust neither until you can calibrate one or the other with a measuring test.