The Master Thesis work has been conducted in the Iveco headquarter in Turin (Italy) with the supervision of the Polytechnic of Turin. It has the aim to develop a reliable multibody model of a heavy-duty vehicle (Iveco Stralis), capable to faithfully reproduce on-road tests. In automotive market, today more than in the past, it is very important to reduce time to market and, mostly, developing costs. So, it is essential to have very accurate models, able to forecast on road behaviors. The multibody environment used is Adams/Car, produced by MSC Software, while Matlab is chosen for the post-processing environment. Furthermore, a complete 3D model was available in CATIA, and Altair Hypermesh, MSC Nastran and MSC Adams/View are used to create flexible bodies.