This document specifies the method for measuring relative wet grip braking performance index to a reference under loaded conditions for new tyres for use on passenger cars on a wet-paved surface. The methods developed are meant to reduce variability. The use of a reference tyre is necessary to limit the variability of the testing procedures. This document applies to all passenger car tyres except for: — special-use tyres marked with "ET"; — T-type temporary spare tyres; — tyres fitted with additional devices to improve traction properties (e.g. studded tyres).