Why GPS Speed Differs From Dashboard Speed
GPS speed and dashboard speed often differ by a small amount. The difference usually comes from how each system measures speed and how each one handles uncertainty.
Different measurement sources
Dashboard speed comes from the vehicle system. GPS speed comes from movement across the ground measured by location updates.
Vehicle calibration and tires
Dashboard speed can shift with tire size, tire pressure, wear, wheel changes, and manufacturer calibration.
GPS signal and smoothing
GPS may smooth readings, lag during acceleration, or jump when signal quality changes. Tunnels and urban canyons can make this more visible.
How to compare fairly
Compare on a straight road with steady speed and clear sky. Sudden acceleration, turns, and poor signal make comparison less meaningful.
Compare your GPS reading
Common questions
Short answers for this guide.
Is a small difference normal?
Yes. A few units of difference can be normal depending on speed, tires, calibration, and GPS signal.
Why does GPS lag when I accelerate?
GPS updates arrive in steps, so fast changes may appear slightly delayed.
Which speed should I follow while driving?
Follow your vehicle instruments and local laws. GPS speed is a secondary reference.