NASCAR issued a technical bulletin Thursday, Sept. 6 that reconfirms the limits NASCAR Sprint Cup Series teams can go in setting up their rear end suspensions in their race cars. Effective Sept. 12, the truck trailing arm front mounting bushing assemblies may be built to allow a maximum of ¼ inch of total movement in one direction only. Truck trailing arm front mounting bushings must be designed to move freely throughout the ¼ inch of approved travel. Previously approved front truck trailing arm bushing assemblies which allow more than ¼ inch of movement or that do not move freely throughout the ¼ inch travel will no longer be permitted for use in competition. Approved front truck trailing arm bushing assemblies must not be altered after being approved. Wheelbase, rear axle location (parallel), offset and rear axle housing alignment will be inspected both pre-race and post-race.
"This doesn’t change any rules that we’ve already had," said John Darby, NASCAR Sprint Cup Series Director. "It reconfirms how far teams can go with their rear suspension setups. Teams have found that with a car’s rear axle steer more is better as it helps with aero and gets the cars through the corners faster. We are just reminding the teams what the limitations are and that they cannot go past these limitations. We will likely address this further in our 2013 rule book."