This wheel exceeds USAC Wheel Standards and specifications for all racing series. Its forged aluminum alloy center is 100% CNC machined to exact tolerances for perfect balance.36-spline forged aluminum center13" diameter x 8" wide4" backspaceInner BeadlockSold IndividuallyExclusive "Roll Forged" rim lip increases bead seat strength-keeps rim rigid and round on the most abusive racing surfaces