Division 6.2.1

In the case of single axles, the lower edge of the outer valance may not be situated beyond the following distances and radii, as measured from the centre of the wheel, except at the lowest extremities that may be rounded (Figure 2 of Annex VI).

where R is the radius of the tyre fitted to the vehicle, and Rv the distance, expressed as a radius, at which the lower edge of the outer valence is situated.