Manufactured from high-quality Swiss 2mm 7075 T6 aluminum, the backbone is strategically CNC machined in low-stress areas to make it as light as possible without affecting strength or rigidity.The strong aluminum backbone protects the bottom of the car from extreme conditions and abusive jumps. The aluminum backbone is perfectly fitted to the composite chassis frame and all holes are perfectly countersunk to provide a smooth surface. The revolutionary and unique chassis design of the XB4 features XRAY Multi-Flex technology. The Swiss 7075 T6 aluminum backbone and composite chassis-plate are firmly mounted together to create a solid framework with each piece playing a distinctive role. The aluminum chassis provides the car with stability and stiffness, while allowing torsional flex along the lengthwise axis.Note:Swiss 7075 T6 is extremely rigid aluminum material and after the hardcoating process in rare cases some small cracks may occur for example, around openings or on edges where tension in the material is highest. Those small cracks are a natural effect and have no negative impact on the performance, reliability, or lifespan of the product and as such are not considered to be a defect.Due the nature of the aluminum material and the machining process, it is normal that the chassis may be slightly bent in the longitudinal direction.