A revised kineto-static model for Phase I tractor rollover

A geometrical model for predicting the rollover initiation angle and tyre contact forces under quasi-static conditions for tractors fitted with front axle pivot is presented. The model uses a kineto-static approach based on two rigid bodies which correspond to: an anterior body, comprising the front axle and wheels (assumed of negligible inertia and mass), and a posterior body, comprising the rear wheels and the remaining machine (with significant inertia and mass). As developed, the model is more suited to fixed-chassis tractors with non-massive front wheels and swing axles. Unlike existing published theory, the new model predicts two types of Phase I rollover. These are initiated by either the rear wheel, or the front wheel losing contact with the slope surface. The most significant result is that the model suggests that activation of full-brake lock on all four tyres may hinder progression into Phase II rollover and this is consistent with the Kutzbach criterion. Although, practically, Phase II may proceed, it would do so at the expense of energy being dissipated at tyre contact points. This extra work could ultimately limit roll-over angular velocities and hence may increase safety. Thus installation of 4-wheel braking systems on all tractors is encouraged.