Incorrect distance tracking in run mode of Spark 3

jnasheim Registered Users Posts: 1
New Traveler
edited January 24 in TomTom Sports
I ran a 14K yesterday and my Spark 3 only tracked 7.93 miles, but I ran 8.7+ miles (according to my chip time).
Is this a known issue? If so, what is the fix?


  • tfarabaugh
    tfarabaugh Posts: 16,938
    How does your chip time tell you the distance? What are you using to gauge the correct distance as a comparative? The nature of GPS is that each data point collected is only accurate to within 15-30m of your actual location. The watch collects the data points and then tries to figure out a route using them (considering that some points may overlap or duplicate). The watch then smooths the data to come up with the most reasonable route taken according to the algorithm it is programmed with. This is why every watch, even two of the same model, will come up with different distances, as they are collecting different GPS data. Even on a certified course the distance is a best case scenario running 18 inches from the curb, not going around anything and taking all tangents. In addition, measured courses add 1 meter per kilometer as a buffer so they are always a bit long. Even championship marathoners actually run longer than 26.2 miles in a race. The exception to this would be running on a track, but this assumes you are in the center lane at all times (plus GPS does not do well on tracks; the constant turning throws off the readings). Trail running is even more inaccurate.

    It is not a known issue, the TT watches are generally considered fairly accurate as compared to the competition. I imagine this is not what you were hoping to hear but let me know if this answered your question. If it did, please mark it as a solution so other can look for it if they have the same question.