A rigid structure enables designers to maintain tight body-panel fit tolerances, tune the suspension for precise ride and handling, help keep the ride squeak- and rattle-free as well as to provide long-term durability and high levels of crash protection for the occupants. The widespread use of high-tensile steel enables the RDX to meet all of these challenges.
Polygonal-shaped frame members, that are designed to disperse and absorb forces in a collision, are located behind the front bumper beam. These high-strength steel frame members send collision forces upward and rearward where they can be absorbed by the main body structure. In the event of a rear collision, polygonal-shaped high-tensile steel frame members direct the loads forward and outward. These rear frame members also use a “wave shape” design that provides high strength, yet deforms controllably in a collision. In a side impact, large longitudinal high-tensile steel side sills extending front to rear underneath the vehicle, along with lateral high tensile steel cross members, absorb energy. For greater steering precision and handling stability, RDX designers paid particular attention to improving body rigidity around the front and rear suspension. These reinforcements are comprised of side-to-side bracing behind and above the firewall and inside the tailgate area.
The use of varying grades of steel in the construction of the RDX’s unit body is key to its stiffness, performance in a collision and light weight. HSS780 grade steel is used in the “box” section of the front, side and rear frame members at the bottom of the body. Additional high tensile steel (HSS780 and 590) is used in other areas under the floor, and in the A- and B-pillars and roof rails. By utilizing high strength steel (39-percent by weight), the RDX exceeds the BMW X3’s torsional rigidity.