How does RaceChrono work-out G-Force?

Hi there, I've got a strange problem and I'm hoping someone can shed some light on it for me. I do the in-car videos for a very slow rally team (68hp 1.3L Skoda!!!) which means there's not much G-Force (+0.5 to -1.0) which means the G-Meter bounces around the 0 point alot going +/- almost constantly which looks wrong.

Does RaceChrono work out the G-Force via the GPS readings or the accelerometer in my N95?

If it's the GPS is there anyway I can smooth the jitteryness (down sample to 2hz etc) and if it's the N95 do I have to have it on a flat surface pointing in the direction of travel etc for the best results?

Many Thanks........................................IanH


  • G-forces are calculated from GPS bearing changes and speed. So unfortunately it does not help you with smoothing down the data.
  • Ah well, thanks for the reply! Guess we need a car with more power :D
  • Hi ianh,
    I did smoothing, I also tried to convince aol that it would be very useful feature.
    What you need to export all data as .csv, then open these data in any math's software (origin, matlab, etc) and then independently for each column (g, speed, etc) do smoothing.
    There are different smoothing filters.
    The simplest is moving average. Of course it is a lot of work and affords if you are never did it. In matlab or origin you may plot data and check what you get. After you satisfied you need to save new data or you may replace old data with new.
    So this is not "list to do" but just idea how to do.
    In the end you will get smoothed and nice data, and on video it looks quite good.
  • I decided to show the effect of smoothing on real data recorded with 5Hz on karting.

    speed was also smoothed.
  • Thanks for that info, I'll give it a try and see what happens!
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