In the recent past, the use of autonomous vehicles is becoming of relevant interest in several fields of application. Personal assistance, precision agriculture, and rescue are just few examples alongside the more common industrial applications. In many cases, the use of articulated structures is preferred to single chassis robots for their peculiar modularity. Moreover, they can be easily provided with locomotion units particularly suitable to overpass obstacles and to move on uneven grounds. Such vehicles are often built as an active front module and a rear one that is pulled passively or that can contribute to the vehicle traction when required. Understanding whether this contribution is convenient or not, it is the main matter of this paper. Two different mobile robots of different scale and purpose are taken into consideration. A dynamic model is presented and experimentally validated to be used as an analysis tool. At last, a simple yet effective actuation law is tested to evaluate the whether the contribution of the back module is beneficial or not to the whole machine manoeuvrability.