ISO 15222:2011 specifies the method for measuring relative wet grip braking performance index to a reference under loaded conditions for new tyres for use on commercial vehicles on a wet-paved surface. The methods developed in ISO 15222:2011 are meant to reduce the variability. The use of a reference tyre is necessary to limit the variability of the testing method procedures. ISO 15222:2011 applies to all truck and bus tyres (commercial vehicle tyres).