The objectives of the tire-noise research being conducted at the GM Research Laboratories are to determine, in detail, the origins of tire noise and, if possible, to use this information to devise methods of quieting tires, particularly truck tires.To date the noise mechanisms that have been investigated relate to the gross airflow around the tire, and the air-pumping between the treads. The first type of noise has been shown to be negligible, even for treadless tires. For the second type of noise, the investigations have centered principally around cross-bar tires where it was felt that the air-pumping mechanism might be most significant, in addition to on-the-road measurements, the study of the air-pumping mechanism has involved mathematical modeling and simulation tests in the laboratory. The measurements have clearly demonstrated the existence of the air-pumping mechanism and show that it is the major contributor to the noise from the type of cross-bar tire tested. Several means are suggested for reducing the noise of the air-pumping mechanism in cross-bar tires.