A passby tire noise test procedure and specification were established as part of General Motor's Tire Performance Criteria (TPC) Program. This procedure was designed to permit testing on various road surfaces at different test sites. As surface texture is one of the most important parameters affecting tire noise a “correction” must be made to normalize the data. The “corrected” noise level of a tire is expressed as the difference (in decibels) between the level of the test tire and that of a control tire run on the same surface.The data acquired in three years of testing are presented. During this period, two different control tires and three test surfaces were used to test nine sizes of Original Equipment (OE) radial tires from five vendors. The following conclusions and recommendations were reached. Conclusions and Recommendations 1.The procedure has satisfied GM's objective of developing radial tires with noise levels as low as the bias belted tires they replace. 2.Use of a control tire to normalize the data is limited to the extent that its noise level varies with road surface in the same manner as does the noise of the test tires. 3.The ASTM skid tire (ASTM Standard Pavement Test Tire E501) is not an ideal noise control tire (with existing road surfaces). 4.Limitations of the control tire procedure can be resolved only by eliminating surface variability. A development program should be undertaken to study the feasibility of testing on a controlled (reproducible) surface. A control tire might still be required to normalize non-surface variables.