Why GPS Tracker and Car Odometer Show Different Mileage

If you've ever compared the mileage recorded by a GPS tracker to your car’s odometer, you may have noticed they don't always match. This discrepancy can confuse drivers and fleet managers alike. So, why does this happen?

1. Different Measurement Methods

• Car Odometer:
  Measures distance based on the rotation of the vehicle’s wheels. It's affected by tire size, tire pressure, and wear, which can alter accuracy.
• GPS Tracker:
  Calculates mileage using satellite-based location points. It estimates distance by measuring the path between GPS coordinates. It's not affected by tire wear, but can suffer from signal loss, urban interference, or route simplification.

2. Common Sources of Discrepancy

• Curvy Roads vs. Straight Lines:
  GPS sometimes draws straight lines between points, missing subtle curves that the car actually drives — resulting in a slightly shorter distance.
• Signal Loss or Weak Reception:
  In tunnels, garages, or remote areas, the GPS signal may drop temporarily, causing under-reporting of the distance.
• Wheel Slip or Rolling at Idle:
  A car odometer may record movement even when the vehicle is rolling slightly while idling, which GPS might ignore if the change in position is minimal.

3. Which One is More Accurate?

• For Legal and Tax Purposes:
  The car’s odometer is typically accepted, but it may overestimate or underestimate slightly.
• For Route Tracking and Fleet Management:
  A well-installed and high-quality GPS tracker is better at logging routes, start/stop times, and monitoring driving behavior.

Conclusion

Both GPS trackers and car odometers have their strengths and weaknesses. Small differences between them are expected and usually not a cause for concern. For businesses managing fleets, GPS tracking adds a valuable layer of data, especially when combined with odometer readings for cross-verification.