A tandem axle system for vehicle having an optimized inter-axle driveline is depicted and described. The system has a forward drive axle system having a forward pinion gear drivingly connected to a drive side of a forward portion of a forward ring gear. The system also has a rear drive axle system having a rear pinion gear drivingly connected to a drive side of a rear portion of a rear ring gear. An inter-axle driveline connects the forward drive axle system with the rear drive axle system.