Despite a real risk of overturning, for the Self-Propelled agricultural Machinery (SPM) the ROPS approach to protect the driver is rather recent. Due to the several SPM categories available on the market, characterized by very different mass, dimension and working functions, the fitting of a ROPS and consequently the check of its strength is complicated. The SPM could be preliminarily divided into at least two categories: - large SPM: combine, forage, potato, sugar-beet and grape harvesters; sprayer; etc.; - small SPM: ride-on tractor, mower, comb side-delivery rake, etc. The most followed approach at present is to define preliminarily the overturning behaviour of the SPM, considering its longitudinal and lateral stability; if a real risk is detected, in order to minimize the likelihood of driver's injury the manufacturer often decides to install a ROPS. The consequent need is to provide some relevant test criteria.