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03 - Coastdown test theory

The test is performed in accordance with **European Directive 70/220/EEC – Annex III** and is based upon statistical evaluation of a minimum of 4 test runs.

The test results are considered to be valid when the statistical accuracy of the average test values is ≤ 2%.

The test can be performed at any speed according to the manufacturer’s requirements, but must follow the general procedure below:

1 | Accelerate the vehicle to a speed 10km/h greater than the test start speed (user definable – 125km/h in the diagram) |

2 | Place gearbox in neutral |

3 | Measure the time taken for the vehicle to decelerate from the start speed to the stop speed (user definable – 85km/h in the diagram). This is time t_{1.} |

4 | Repeat steps 1-3, but in the opposite direction. This is time t_{2} |

5 | Take the average time of these two test runs (t + _{1}t)/2. This is the time _{2}T |

Repeat steps 1 to 5 until such time that the statistical accuracy of the average is not more than **2% **

** **

The statistical accuracy (*p*) is defined by:

Where:

= Coefficient given by the table below,

*n* = Number of tests

*s* = standard deviation

n | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |

t | 3.2 | 2.8 | 2.6 | 2.5 | 2.4 | 2.3 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 | 2.2 |

1.6 | 1.25 | 1.06 | 0.94 | 0.85 | 0.77 | 0.73 | 0.66 | 0.64 | 0.61 | 0.59 | 0.57 |

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