Tire noise research at the GM Research Laboratories has centered around on-the-road testing with a variable-loading, single-wheel trailer consisting essentially of a truck wheel at the end of a forty foot beam. This approach has proved to be highly satisfactory since it can be used to make realistic tests of the noise from a single truck tire, in isolation from other noise sources and free from interference by echoes from the vehicle structure.Measurement procedures have been developed both for semi-circular arrays of microphones on the ground and microphones and accelerometers traveling with the test tire. For the stationary semi-circular arrays, a digital analysis procedure has been developed to determine the narrow-band spectra and the radiation patterns of the sound emitted by the moving tire as it passes through the center of the semi-circular array. The associated computation includes corrections for the varying source-receiver distance during the time interval of the data, small run-to-run variations in the test conditions, and Doppler shift. In this way the power spectra and the radiation patterns are determined as if the semi-circular array were moving with the tire at a fixed radius. For microphones moving with the trailer, signal averaging methods are utilized to reduce background noise, especially wind noise. Also a new coherence-function method that eliminates wind noise in a system of three microphones has recently been developed and is currently being used for far-field measurements.The tire noise trailer could be used for development work as well as for research. It might also be considered for qualifying tires.