A model and comparison of 4-wheel-drive fixed-chassis tractor rollover during Phase I

• Parametric model of tractor rollover initiation for tractors with front mass.
• Mass partition properties of tractors important for stability calculation.
• Model predicts effect of front mass is significant in terms of stability.
• Application of brakes to all wheels potentially reduces full rollover likelihood.

A general model to predict quasi-static articulated tractor instability on a slope has been derived using kineto-static modelling. Under simplifying assumptions, it is possible to model fixed-chassis tractors and, in particular, include the effect of front axle-wheel mass. The model is therefore used in this paper to investigate the effect of front body mass on tractor stability and behaviour during Phase I rollover. The results are of particular relevance to four-wheel-drive (4WD) tractors. The change in potential energy for fixed-chassis tractors during Phase I rollover is also evaluated. The effects of mass partitioning are displayed graphically. It is shown that the stability of a tractor depends on the position of the centre of gravity (COG) of the main (posterior) body. For tractors with massive front wheels, tyres and beam axles, this COG is likely not to be the same as that found from the standard COG methods currently adopted.