The numerical and modeling errors in computational aerodynamics consist of several components. The errors have been shown to be large at the front in the stagnation region and in the rear in the base region, see Ramnefors et. al. (1996). This paper presents results from numerical simulations of the flow around a simplified Volvo FH truck. Experimental data have been created for comparison in the Volvo Wind-tunnel. Simulation of the flow around the truck using several turbulence models and numerical schemes are compared to experimental measurements of drag, surface pressure distribution and total pressure distribution in the wake. It was found that the numerical scheme is very important for the base pressure. Several turbulence models have been tested. The models range from simple linear eddy viscosity models, EVMs, to more complex models such as non-linear EVMs and Reynolds stress transport models. The errors are shown to be surprisingly large along the roof of the truck.