The ability of a simulation model to accurately predict vehicle response is investigated in this paper. This study seeks to compare full-scale tractor-semitrailer straight-line braking test data to predicted response from a detailed heavy truck computer vehicle dynamics simulation model. The model, Simulation MOdel Non-linear (SIMON), is a vehicle dynamic simulation model within the Human Vehicle Environment (HVE) software environment. This computer program includes a vehicle dynamic model capable of simulating vehicle motion in 3-dimensional environments and includes Brake Designer and ABS Simulation Models. The results of several days of full scale instrumented testing of a tractor-semitrailer performed at the Transportation Research Center, in East Liberty, Ohio are presented. Instrumented braking tests were performed at two speeds of 13.4 m/s (30 mph) and 27 m/s (60 mph) for 2 primary configurations including an unloaded semitrailer configuration ( LLCW ) and a full gross vehicle weight condition (GCW). In addition various wheel brakes were disabled symmetrically and asymmetrically for each of the above conditions to evaluate the tractor-trailer response. These straight-line braking tests were performed on dry concrete surfaces. Vehicle parameters and inputs for the computer simulation models were obtained from the actual vehicle or motor vehicle manufacturer's specifications and each test's individual configuration. The simulation results, in terms of vehicle dynamics responses, are compared to the full-scale test data. The simulations were modified and tuned to simulate full-treadle braking with all brakes functioning correctly, as well as the behavior of the rig under full braking with selected brakes disabled. Comparisons allow validation of the computer simulation model against real-world test data under many real-world conditions. The process of tuning the model is discussed in terms of the tradeoffs considered. The effects of vehicle configuration variations are also analyzed and presented in this paper.