springs are the biggest culprit in rough ride, stiff ones especially. but having soft shocks or worn shocks that don't have the necessary compression to take the edge off sharp impacts don't help either. the bilsteins hd may be too hard for u. maybe the bilsteins touring class shocks would be a better fit. as for low tire psi...highly not recommended. low tire pressue (below 30) just doesn't provide enough support for the tires to support the car. extra heat is generated, vulnerable to pot holes for both wheel and tires. blow outs possible at high speed.