Comparing the influence of Roll-Over Protective Structure type on tractor lateral stability

Tractor overturns are a major cause of death in agriculture. Many variables are involved. The Roll-Over Protective Structure (ROPS) has been invented to minimise the risks of driver injuries in a tractor overturn. Narrow-track tractors for orchard and vineyard operations are mainly available with two different ROPS types: an enclosed cab frequently fitted with filters and air-conditioning system or a simple two post ROPS designed to be folded down to allow the tractor to operate in a reduced surrounding space. Concerning stability, the tractor lateral stability angle is the result of the tractor configuration and its position with respect to the ground slope. The aim of the paper was to study the effect of ROPS type on tractor stability performance. The tractor stability parameters were evaluated on 22 modern narrow-track tractors measuring mass, track-width, wheelbase, Centre of Gravity (CoG) and Moments of Inertia (Mol). The evaluation considered pairs of tractors equipped with two post ROPS and cab ROPS. In the design of compact narrow-track tractors the cab fitment keeps the wheelbase and track-width of the tractor unchanged with respect to the front foldable ROPS but affects the mass, position of the CoG and longitudinal and transversal Mol. Data show an increase in tractor mass and higher CoG and Mol for the cab fitment with respect to the two post ROPS. A recent international debate on the safety performance of two post ROPS was consequent to the incorrect use of the foldable ROPS in field operations. Cab ROPS is thus often claimed to provide higher protection to the driver. This investigation denotes that on sloping fields narrow-track tractors fitted with a cab ROPS reach the lateral unstable state at a lower angle than two post ROPS tractors; consequently, the stability performance of the tractor worsens.