Abstract: A new random footprint tire model was developed, which can reflect both the vertical and the horizontal stimulation at the same time. It was used to review the tractor trailer combination longitudinal smoothness. A corresponding dynamic vehicle model was established. The computer simulation to the vehicle model in time domain about the determinated function of road stimulation was carried out. The effects on the towing attachment longitudinal dynamic forces of the tractor trailer combination were analyzed. Experimental study with two different towing attachments, i.e. rigid towing attachment and pliable towing attachment was performed. A comparison of the results obtained by the simulation with available experimental data shows very good agreement.