Abstract: A method of estimating contact forces between the wheels of a railway wagon and a rail track, for use in determining information such as the likelihood of derailment. Accelerations of the body of the wagon are measured using motion sensors located at suitable points on the body. Forces on the side frames of the wagon are calculated based on the accelerations of the body and predetermined parameters of the body. Forces on the wheels of the wagon are calculated based on the accelerations of the body and predetermined parameters of the body. The contact forces between the wheels and the rails are then calculated based on the forces calculated for the side frames and the wheels. The calculations are carried out using an inverse model of the wagon system. Equipment which implements the method is also described.