Why is my mileage report different from my odometer

May 21, 2024

There are several factors to consider whether looking at the total mileage over a long period or a single trip.

  • 1

    The precision of the car's speedometer/odometer.
  • 2

    The tire size
  • 3

    How to use GPS

Odometer

In general, a vehicle’s odometer will never give the same reading as GPS. This is also true between two vehicles or two uncalibrated measuring instruments.

It should be known that car odometers are not very precise measuring instruments, and they have no official calibration. On average, in the industry, the best accuracy is within -2.5% and +2.5% (possible variation of 5%).

Please be aware that an odometer can be defective and is not an absolute measuring standard.

(Honda has had to modify some leases because the speedometer on certain models showed up to 15% more than reality, which resulted in 15% more mileage.)

Tires

Not only can the instrument have a variation in reading, but external factors, of a mechanical nature, can also vary the speed reading and therefore the mileage.

Among the most common factors, apart from the car instrument (the odometer), are the type, size, condition of wear, tire pressure and season. This variation can also be between -2.5% and 2.5%.

As speed sensors are directly connected to the transmission, tire diameter will impose a variation. Winter driving also involves slight differences due to false distance recording caused by slipping.

The table below helps to better understand why there are variations.
In this example, two tire models of the same 16-inch dimension are compared.

The tire model #1 has a tread life of 539 revolutions per kilometer, while the tire model #2 has a tread life of 531 revolutions per kilometer.

It is understandable that a car equipped with tire model #1 will display more kilometers on the odometer than a car equipped with tire model #2.

In the table, the displayed speed of 110 km/h is actually 111.3 km/h, a variation of 1.2%.

Therefore, it is normal for the odometer not to match 100% with that of the GPS.

Addition of many causes

The GPS accuracy is usually more precise than other measuring methods. However, this accuracy can be affected by the items listed in the GPS Usage section.

It should be noted that tire size and odometer precision can add up and produce results that are between 10% and 15% different compared to GPS.

GPS usage

Other factors may cause the annual mileage of the vehicle to not match the GPS report. For example:

– The GPS is not always in use, if it was disconnected at one point and the user used the vehicle without the GPS. (lack of data)


– The user is using a cable that does not constantly power the instrument, causing delays at the beginning of each trip and therefore not corresponding to the total. (loss of several meters at the beginning of each trip)


– The user starts from a garage or other place without a signal and does not wait for the GPS to function and still drives. (loss of several meters up to a kilometer at the beginning of each trip)


– The instrument is poorly installed and cannot always connect to satellites or lose the signal.


– The GPS has not been downloaded and data has been lost or erased.


– The user prints a business report, but does not always press the business sorting button. It seems that some trips are missing, but in fact, several business trips are classified as personal and do not display.

about the technology

We have included some articles on this topic, unfortunately they are in English (with Google translation).

In general, when there is a difference, the precision of the car odometer vs. that of the GPS is in favor of the GPS. There is no evidence that the odometer of a particular vehicle is more or less accurate than that of another unless a precision calibration is done on both vehicles.

In the case of TripLogik, we use the largest antenna available on the market, which allows the instrument to receive maximum signal and be as precise as possible with current technology.

New generations of GPS antennas since 2018 have a reaction speed of starting movement 3x faster than the first models of 2007. As technology becomes available, we integrate it into new models to always improve the product.

Of course, the GPS device must be positioned as recommended in the installation manual and the accuracy may vary slightly depending on weather or geographic conditions.

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