Phone Speedometer vs Car Dashboard
A phone GPS speedometer and a car dashboard often show slightly different values because they measure speed from different sources. That difference is normal and useful to understand.
How the phone measures speed
A phone estimates ground speed from GPS position updates. It does not know wheel rotation or tire size.
How the dashboard measures speed
A car dashboard usually estimates speed from the vehicle system and wheel movement. Calibration and tire changes can affect the number.
Why the numbers differ
Dashboards often read slightly high by design, while GPS can lag, smooth, or jump when signal quality changes.
How to compare them
Compare at steady speed, on a straight road, with clear sky and stable GPS. Avoid comparing during quick acceleration or tunnels.
Check a second speed reading
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Which one should I follow while driving?
Follow your vehicle dashboard and local traffic laws. Phone GPS is a secondary reference.
Why does my phone show lower speed?
The dashboard may read high, or the phone may be smoothing GPS updates.
Can tire size affect dashboard speed?
Yes. Tire size, wear, pressure, and wheel changes can affect dashboard speed estimates.