Applicability to Narrow-Track Tractors of an Official Standard for the Calculation of Self-propelled Agricultural Machines Stability

Agriculture is still one of the high risk sectors for the health and safety of operators. Improvements are necessary to decrease injuries and casualties. Overturning agricultural tractors is a common accident that occurs every year in Italy, resulting in more than a hundred victims. Currently, there are no general rules specifically dedicated to the assessment of the stability of conventional agricultural tractors. On the other hand, the design of narrow-track tractors (used in vineyards, orchards, horticulture and greenhouses) makes them unstable, especially when facing lateral overturning. For this, the fitting of a front-mounted roll bar requires specific tractor stability requirements. Diversely, ISO 16231, which applies to self-propelled agricultural machinery, is founded on a sample approach that takes into account geometric parameters to evaluate vehicle stability. In this paper, the results of the ISO 16231 algorithm were compared with the limit angle of static lateral stability of some tractor models (both narrow-tracked and conventional) tested on a tilting platform. The results confirm that the ISO standard approach is correct if the main purpose of its application is to establish minimum requirements. The inaccuracy in applying ISO 16231 to agricultural tractors would prevent its adoption from replacing the actual overturning test.