ISO 9815:2010 specifies a lateral stability test for passenger-car and trailer combinations. It is applicable to passenger cars in accordance with ISO 3833, and also to light trucks, and their trailer combinations.
The lateral stability test determines the damping characteristic of the yaw oscillation of such towing-vehicle–trailer combinations excited by a defined steering impulse. The combination is initially driven in a steady-state, straight-ahead driving condition. Oscillation of the vehicle is then initiated by the application of a single impulse of steering, followed by a period in which steering is held fixed and the oscillation of the combination is allowed to damp out. Testing is conducted at several constant speeds. Where non-periodic instability is of interest, a steady-state circular test is specified.