This International Standard describes spare unit substitutive equipment (SUSE) for passenger car tyres, which is designed to enable users to continue their journey (with or without a stop) in a reasonably safe manner. NOTE 1 Certain equipment becomes effective automatically, thus avoiding the need to stop the vehicle immediately for inspection and corrective action. This International Standard is intended only to qualify the performance of extended mobility systems. Its specifications only apply to extended mobility systems that can permit the extended mobility of the vehicle. NOTE 2 Other types of SUSE are described in Annexes A and B. The specifications in this International Standard apply from the moment the extended mobility system becomes effective, with the driver continuing to control of the vehicle (in terms of speed and direction) in an attempt to reach an appropriate place for servicing. The following are within the scope of this International Standard: - the description of the various types of SUSE; - the description and performance levels of complete extended mobility systems. NOTE 3 The performance level that the user reasonably has the right to expect, as well as the restrictive conditions placed upon that level, can vary to a large degree depending on the equipment installed and on the real operating conditions of the tyre in flat-tyre running mode. The following are outside the scope of this International Standard: - the vehicle to be equipped; - the tyre while operating in inflated mode; - the characteristics of the pressure survey device and of the warning function relative to the inflated mode or to the partially deflated mode due to slow pressure losses; - the transitory phase, if any, before the equipment becomes effective; - the inspection, assessment, and the servicing of the extended mobility system, after it has been activated in flat tyre running mode.