Fundamentals of Navigational Rallying | Interpretations of Roads | Ball & Arrow (Tulip) Navigation | Time Calculations | Calibration Runs | Route Classification

Calibrating your car is necessary to ensure your on-time performance is as good as it can be. You need to be sure your Odometer readings are the same as the ones used by the plotters of the event. This is done by calibrating your car’s odometer against a fixed, standard distance. CARS has established standard Calibration Runs in North, Central and South Trinidad for use by the plotters and competitors of our rallies.

To calibrate your car, simply follow these steps:

1. Ensure your car’s tyre pressure is what it should be.

2. Align your car’s front tyres with the start line of the Calibration Run.

3. Zero your car’s trip-meter if possible, or note your current odometer reading.

4. Drive to the end of the Calibration Run (avoid overtaking).

5. Align your car’s front tyres with the finish line the same way you did at the start.

6. Note the trip-meter reading, or subtract your start odometer reading from your end reading

If your odometer reading is different from the Calibration Distance, whether higher or lower, then your car is out of calibration. Your car’s Calibration Factor is a constant value, which when multiplied by the distance read off your car’s odometer, will give the Corrected Distance.

7. Calibration Factor = Calibration Distance / Odometer Reading

8. Corrected Distance = Odometer Reading * Calibration Factor

9. Example:
On a 10 km calibration run, your car’s trip-meter read 10.2 km. You enter a rally with an average speed of 20 kph. After 10 km, you meet a checkpoint. What is the error in your Elapsed Time if you ignore the calibration information?

* Timing Factor = 60 / 20 = 3 min per km (see Time Calculations)
* Wrong Elapsed Time = 10 * 3 = 30 min from start.
* Calibration Factor = 10 / 10.2 = 0.98
* Corrected Distance = 10 * 0.98 = 9.8 km
* Correct Elapsed Time = 9.8 * 3 = 29.4 min from start.

Since you round down to the minute, your correct Elapsed Time would put you 1 minute late at the checkpoint and you would continue running progressively later by 1 minute for each 10 km rallied (a typical rally covers over 50 kms).

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