All speedometer guides

Written by Muneeb Rana · Last updated 26 October 2026

Quick answer: These speedometer guides cover every topic on this site: how GPS speed works and how accurate it is, HUD and odometers, speed units, troubleshooting, road safety and laws, and benchmarks for walking, running, cycling and travel. Each guide cites sources and repeats our safety note: set up before you move.

TL;DR

• Every guide.
• Grouped by topic.
• Sources cited.
• Safety notes.
• Updated 2026.

Speedometer guides: speed and GPS

• How accurate is a GPS speedometer?: GPS speedometer accuracy explained: why speed from Doppler is often within about 1 km/h in open sky, and where tunnels, cities and slow speeds break it.
• GPS vs car speedometer: which one is right?: GPS vs car speedometer: why your dashboard usually reads a few percent above GPS, what the rules allow, and when to trust each reading.
• Why car speedometers read high: Why car speedometers read high: the regulations that forbid under-reading, tyre wear, tolerances, and how to measure your own car's error with GPS.
• Speedometer tolerance rules explained: Speedometer tolerance rules: UN ECE Regulation 39's formula, worked examples, how odometers fit in, and why these limits are not speeding tolerances.
• How to check speedometer accuracy: How to check speedometer accuracy safely: a step-by-step GPS method, mile-marker timing, what gaps are normal, and when to see a mechanic.
• How tire size changes speedometer error: Tire size speedometer error explained: how bigger or smaller tyres change your speed and odometer readings, worked examples, and how to verify with GPS.
• How GPS speedometers work: How GPS speedometers work: satellites, trilateration, Doppler velocity, multiple constellations and filtering, explained in plain language for app users.
• How to improve GPS signal: How to improve GPS signal for speedometer and map apps: precise location, sky view, mounts, battery savers, A-GNSS and when to restart your phone.
• GPS in tunnels: why speed freezes: GPS in tunnels loses satellite signals, so speedometer apps freeze or drop to zero. Why it happens, how cars and nav apps cope, and what to do.
• Can a speedometer work without GPS?: Speedometer no GPS: how cars, bike sensors and phones measure speed without satellites, why phone apps still need location, and the alternatives.
• GPS speedometer vs radar speed: Speedometer vs radar: how police radar and GPS apps measure speed, why readings can differ, and why a phone app is not evidence. Plain-English guide.
• Average speed vs max speed: Average speed vs max speed explained: how trip meters calculate each, why stops lower your average, GPS spikes in max speed, and how to read your trips.
• How to measure top speed: How to measure top speed with a GPS app: settings, why GPS spikes fake a max, sampling rates, and doing it only where it is legal and safe.
• What is a velocimeter?: What is a velocimeter? Another word for a speed-measuring instrument. How it relates to speedometers, anemometers, pitot tubes and GPS speed apps.

Safety and laws

• Phone mount placement: where to put your phone: Phone mount placement for driving: where to put a phone for GPS and visibility without blocking your view or airbags, plus what the law says.
• Phone use while driving laws: Phone use while driving laws: hand-held bans, texting bans and mounting rules in the US and UK, why they exist, and how to use a speedometer app legally.
• The dangers of speeding: Dangers of speeding: how speed increases crash risk, stopping distance and injury severity, with WHO, NHTSA and IIHS evidence and practical habits.
• US speed limits explained: US speed limits explained: who sets them, typical urban, rural and interstate limits, school zones, and why you must follow posted signs, not averages.
• Speed limit app: what to look for: Speed limit app guide: how apps get limit data, why it is often wrong, features worth having, and why Speedometer PRO does not show limits today.

Phone features the app does not include

• Android Auto Speedometer and CarPlay Speedometer Apps: Is there an Android Auto speedometer or CarPlay speedometer app? What Google and Apple allow on the car screen, what works instead, and safe setup.
• Video Speedometer App: Recording Speed on Video: How a video speedometer app or camera speedometer app overlays GPS speed on video, how accurate the overlay is, privacy and legal checks, and what to use.
• Tachometer App: How Phones Measure Engine RPM: How a tachometer app gets engine RPM: OBD-II adapter, engine sound or GPS math. Accuracy of each, a worked RPM formula and when you need a real tachometer.

Other guides

• Speed units and benchmarks: see the MPH guide
• Odometers and trips: see the odometer guide
• Heads-up display: see the HUD guide
• Activities: see use cases
• Calculators: see free tools

Get Speedometer PRO on Google Play · Download on the App Store · Set it up before you move; never handle your phone while driving.

Sources

• GPS Accuracy (GPS.gov): gps.gov (accessed 26 October 2026)
• Speeding (NHTSA): nhtsa.gov (accessed 26 October 2026)