The Western Star Extreme Duty (XD) Offroad MBT-40 Transformerchassis is engineered specifically for extremely rugged environments. The XD Offroad MBT-40, dubbed the Multi-Body Transformer, is capable of transforming from one fully functional body to another in a minimal amount of time. The XD Offroad is available on both the Western Star 4900 and 6900 models. The 6900XD comes in both 6x4 and 6x6 configurations.