Among many potential problems associated with passenger cars, the problem regarded as most sensitive and important to the customers is the passenger car’s quietness. In particular, because the trend toward the high-performance passenger cars is increasing, the quietness should be considered reflecting the increasing demand of the customers for the comfort of passenger car ride. Road noises are of low-frequency in the region of 20Hz to 350Hz, generated when the tires are making contacts with the rough road surface while the passenger car is running, in which the noises are resonating within the passenger compartment or with the passenger car suspension. In this research, among the factors related to the road noises, the influencing factors associated with the suspension and the tire design were investigated. In particular, among the tire design factors, the structure and the rubber material were investigated as the influencing factors, and for the investigative purpose, experimental tires were manufactured and road noise evaluations were conducted thorough actual feeling tests. Then the test results and correlations were analyzed using the 6-Sigma statistical method.