Starting from the consideration that the performances of the present engines for trucks are each day more powerful, with direct implications in the transport speed, the designers has to built chassis according to EURO 4 rules, where the security standards for passive and active safety are very hard to achieve, it is obvious that the dynamic analyze of such a chassis it has to be done. The classical methods of analyze are taking into account a shaft of the transmission of the truck, as the reference shaft. The cinematic chain after the reference shaft is modified based on some simplifying hypothesis with the disadvantage of a lower calculus precision. Using the F.E.M. analyze on dynamic conditions of the chassis, those simplifying hypothesis are eliminated.