I think it's worth noting that a scenario exists where it becomes mathematically correct to treat the front and rear as oscillating independently. It depends on the value of the pitch inertia relative to vehicle mass and CG location.But thanks to progress over the last ninety odd years this rather simple 2-D problem has been dumbed-down to 2 x 1-D problems (ie. two totally independent, and unrealistic, 1 DoF spring-mass systems).