A full-scale square-back Ahmed body is analysed experimentally and numerically for a free-stream flow velocity of 45 m/s corresponding to a Reynolds number Re H = 7.7 × 10 5. Numerical simulations are performed for matching inflow conditions and different turbulence models. The main goal of this study is to examine the effectiveness of the Delayed Detached Eddy Simulations and the Reynolds Averaged Navier-Stokes k − ω SST turbulence model to capture the mean flow physics. Local and global aerodynamic parameters are compared with experimental results, including boundary-layer parameters evolving over the roof, the wake characteristics, the shear layer, and the mass entrained into the wake. A particularly good agreement is found between the experiment and the DDES. An indepth analysis of the shear-layer growth, mass-entrainment and momentum budget analyses along the recirculation region interface, allow for identifying and quantifying the differences in predicting drag and the mechanisms at stake between the different approaches. The momentum budget, performed on the experimental data shows that pressure can be accurately obtained from experiments and closely follows that computed from high-fidelity numerical simulations. These results confirm the effectiveness of DDES in studying flows at high Reynolds numbers. The mass/momentum budget along the recirculation-region interface is also found as a possible mean to quantify road vehicle's aerodynamic performances, naturally extending to more complex geometries.