Karoo 3: speed sensor auto or manual insertion

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Simone Messina

• November 21, 2025 08:01

I was riding with a speed sensor but i noticed distance differrence in usual ride compared when i rode withpout speed sensor. Is it not easy to have correct wheel circumference. I made 10 wheel spins to measure distance / 10.

The question is will be better to have speed sensor auto calibration or circumference manual insertion. Which mode will i have less error?

 

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  Christian Renner

  • November 24, 2025 12:53
  • Edited

  I have answered your other post: if you use BLE, it is not going to give proper results (auto-calibration is even worse), unless you set up a wrong circumference until you obtain correct distance results. ANT+ should be working ok, but the number of connections is limited.

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  Simone Messina

  • December 02, 2025 10:32

  i was using ANT+, the error could came form circumference i setted up. But i think auto calibration culd have more error,

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  Simon Lockwood

  • December 04, 2025 17:59

  Why do you feel the need to have a speed sensor for a GPS computor? I use one when on the rollers doing workouts, just to give some KMs for strava, but remove it when riding outdoors. 

  Simon

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  Christian Renner

  • December 04, 2025 19:29

  Hi Simon, I don't this solves the actual problem. If the Karoo has the ability to connect to a speed sensor, it should work.

  Apart from that, there are several cases where a speed sensor makes a lot of sense:

  - GPS does not work in tunnels (computer could auto-pause and/or record wrong distances).

  - GPS does not work well in the forest (gravel, MTB).

  - GPS speeds can be jumpy.

  - GPS needs time to get a fix (particularly if you did not have wireless connectivity for some time). This can cause very wrong positions, speeds, distances w/o a speed sensor *or* you need to wait before starting a ride. Nothing I fancy.

  There are likely more cases. I had issues with all of the above, so I am also using a speed sensor on a GPS computer.

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  Christian Renner

  • December 04, 2025 19:33

  Simone, my post get deleted again (not sure why). Auto calibration with ANT+ works very well for me. Well below 1% error. For manual setup, I would ride and finally compare Strava or Komoot distances of the route with the recorded ride and adjust the circumference a few times, until it converges (get the ratio of recorded and actual distance and multiply that with the current circumference). This has worked nicely for me. However, values my change and depend on tire pressure, etc.

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  Simone Messina

  • December 07, 2025 07:38

  I measured 20 wheel spina. Yesterday i have done a 90 km ride. Karoo when Speed sensor says 90 km and Strava correctiom says 89,3 km. 700 meters errore could be acceptable.

  But how It affect Speed and max Speed?

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  Christian Renner

  • December 07, 2025 19:41

  Your Karoo is overreporting by ca, 0.8%. You could lower the circumference be this amount (e.g., if you have 2150mm, correct to 2133mm).

  With above values, your speed will also report 0.8% too high (assuming that the Strava distance is correct). If you have an average speed of 30 km/h, the Karoo will report ca. 30.2 km/h. If you have a max. speed of 60 km/h, Karoo will report 60.5 km/h.

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