In this paper, a new approach in estimating the lateral tire forces and hitch-forces of a vehicle–trailer system is introduced. It is shown that the proposed hitch-force estimation is independent of trailer mass and geometry, by utilizing the vehicle velocity, acceleration, torque engine, wheel's speed, and steering angle measurements. The designed lateral tire forces and hitch-force estimations' algorithm can be used for any ball type trailer without any priori information on the trailer parameters. A vehicle–trailer dynamic model is proposed to design an observer for the estimation of the hitch-forces and lateral tire forces. Simulations' studies in carsim along with experimental tests are used to validate the presented method. The results confirm the accuracy of the developed observer, and the experimental tests' results show that there is a good agreement between the estimated and actual lateral tire forces as well as the hitch-forces.