Static Lateral Stability of Tractor with Rear Wheel Ballast Weights: Comparison of ISO 16231-2 (2015) with Experimental Data Regarding Tyre Deformation

The paper presents a static lateral stability of a sub-compact tractor MT8-070 Mini in relation to a safe tractor operation. Axle weight distribution of the tractor was measured to calculate the vertical and longitudinal coordinates of a centre of gravity (COG). Experiments were aimed at the tractor equipped with no and four levels of rear wheel ballast weights (30.5, 61, 91.5 and 122 kg) at standard and extended overall width on tyres. A static overturning angle was calculated and experimentally measured when the tractor with right wheels touching the ground was in a state of unstable equilibrium. Comparing the experimental data with ISO 16231-2 (2015), the differences were 2.57%, 2.80%, 3.04%, 3.42% and 3.88% in the case of the standard overall width on tyres and 2.40%, 2.61%, 3.11%, 3.67% and 3.99% in the case of the extended overall width on tyres at 0, 30.5, 91.5 and 122 kg of the rear wheel ballast weight. Considering the vertical tyre deformation and the lateral shift of the tyre, the differences decreased to 0.95%, 1.11%, 1.29%, 1.85% and 1.42% (standard overall width on tyres) and 0.91%, 1.18%, 1.69%, 2.27% and 2.57% (extended overall width on tyres). The length of a rubber lug of a tyre contact patch did not change when the tractor was inclined at various ballast weights and did not affect the static overturning angle calculation according to ISO 16231-2 (2015). Results showed higher static overturning angle experimentally measured in comparison with calculated according to ISO 16231-2 (2015) due to the tyre deformation. Limiting the tractor operation on the basis of the static overturning angle calculated according to ISO 16231-2 (2015) avoids the tractor usage under dangerous operation conditions.