This study was conducted to identify and better understand the predominant noise generation mechanisms of cross lug truck tires. These tires are often used on the drive axles of heavy trucks and have been found to be the principal contributor to exterior truck noise at highway speeds (1 and 2).* The end product of this study was to establish tread pattern design guidelines.Two primary noise mechanisms of cross lug tires, tread vibration and air pumping, were identified and analyzed experimentally. The system inputs were determined, laboratory simulations run and experimental tests devised to differentiate between the mechanisms.The conclusions reached are that both air pumping and vibration-caused noise are present in most truck tires. The predominating mechanism depends on the tread pattern, state of tread wear, road surface macrotexture, tire loading and vehicle speed.