Division 4.3.2.4 Vehicle coastdown procedure

The measurements shall be carried out in opposite directions until a minimum of ten consecutive runs (five in each direction) have been obtained. Should an individual run fail to satisfy the required on-board anemometry test conditions, that run and the corresponding run in the opposite direction shall be rejected. All valid pairs shall be included in the final analysis with a minimum of 5 pairs of coastdown runs. See paragraph 4.3.2.6.10. of this Sub-Annex for statistical validation criteria.

The anemometer shall be installed in a position such that the effect on the operating characteristics of the vehicle is minimised.

The anemometer shall be installed according to one of the options below:

1. (a)

   Using a boom approximately 2 metres in front of the vehicle’s forward aerodynamic stagnation point;

2. (b)

   On the roof of the vehicle at its centreline. If possible, the anemometer shall be mounted within 30 cm from the top of the windshield.

3. (c)

   On the engine compartment cover of the vehicle at its centreline, mounted at the midpoint position between the vehicle front and the base of the windshield.

In all cases, the anemometer shall be mounted parallel to the road surface. In the event that positions (b) or (c) are used, the coastdown results shall be analytically adjusted for the additional aerodynamic drag induced by the anemometer. The adjustment shall be made by testing the coastdown vehicle in a wind tunnel both with and without the anemometer installed in the same position as used on the track., The calculated difference shall be the incremental aerodynamic drag coefficient C_D combined with the frontal area, which shall be used to correct the coastdown results.