GPS speed test · Car

Car Speed Test

This GPS car speed test turns your phone into a live speedometer. Compare your speed with the dashboard, set a speed alert, or flip to HUD mode and read your speed off the windshield at night.

GPS off

0KM/H

Max speed: —
Avg (moving): —
Distance: —
Trip time: —
Moving time: —
Heading: —

Set Speed Alert

Speed limitkm/h

Beep and vibrate when exceeding this speed.

Trip log

No points recorded yet

Live GPS speed
HUD windshield mode
Speed alert with beep
Keeps the screen on
GPX trip export
Location stays on your device

How it works

Test Your Car Speed in 3 Easy Steps

01
Mount Device
Place phone securely in windshield cradle with clear sky view.
02
Start GPS
Tap Start and accept browser location access.
03
Compare Gauges
Maintain steady speed and observe the true difference between dashboard and GPS.

Regulations

Why Your Dashboard Reads Higher (UN ECE Regulation 39)

Automotive regulations strictly forbid car speedometers from ever displaying lower than true speed.

Why Your Dashboard Reads Higher (UN ECE Regulation 39)
True Speed (GPS)	Permitted Dashboard Display (ECE 39)
30 km/h	30–37 km/h
50 km/h	50–59 km/h
80 km/h	80–92 km/h
100 km/h	100–114 km/h
120 km/h	120–136 km/h

Under international automotive law, speedometers must satisfy: 0 ≤ (V1 – V2) ≤ 0.1 V2 + 4 km/h. At 100 km/h, your car speedometer is legally permitted to read up to 114 km/h.

HUD Mode

Windshield Mirror Display for Night Driving

Turn your smartphone into a reflection heads-up display.

Activate HUD mode, set brightness to maximum, and place your phone on the dash directly in front of the steering wheel at night.

Safety

Crucial Driving Safety Rules

Never adjust or hold your phone while driving.

Passenger Operation Only

Have a passenger manage tests or configure mounts before pulling out onto the road.

Obey Road Signs

Speed limits and road conditions always take precedence over experimental digital tools.

Stopping Distance Calculator.

FAQ

Car Speed Test FAQ

Why does my car speedometer show a higher speed than SpeedReflex GPS?

Vehicle dashboards are legally mandated to never under-report vehicle speed and typically display 3% to 8% higher than true velocity to prevent accidental speeding.

How accurate is a GPS car speedometer?

Under open sky, GPS speedometers on modern smartphones are accurate to within 1–2 km/h because they use satellite Doppler shift calculations.

Is it legal to use a phone GPS speedometer in a car?

Yes, provided your smartphone is mounted securely in a dedicated cradle and you do not hold or operate the device with your hands while driving.

Related Tools

Car Speed Test

Test Your Car Speed in 3 Easy Steps

Mount Device

Start GPS

Compare Gauges