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Coast-by tire road noise is much effected by temperature. As temperature goes up, coast-by tire road noise level becomes lower in the case of passenger car tire. Temperature gradient of coast-by tire road noise is around -0.07 dB(A)/°C using air temperature. On the other hand, the tire is under torque during a pass-by test and some amount of extra noise is radiated from the tire pavement interface. Generally speaking, the level of tire road noise during pass-by mode becomes higher than coast-by mode. How much tire road noise is increased due to the applied torque and how its extra noise is effected by air temperature are reported here. Pass-by tire road noise consists of two components. The first component is the coast-by noise and the second component is the extra noise by the torque that is obtained by the noise level calculation of pass-by minus coast-by.

In order to evaluate and improve the level of tire road component noise, test methods for the tire road component noise separated from the whole vehicle noise have been studied. The trailer method is one of the best methods in a sense of eliminating the vehicle influence. However, the accuracy of the trailer method greatly depends on the technique of tow vehicle noise correction. The most basic and complete correction technique is the time history correction method that is mainly used in the academic research field because of its accuracy. However, the time history correction method requires a rather complicated signal subtraction process in time domain. Therefore it is difficult to use in daily practical testing for tire development. Instead of the time history correction method, the long drawbar method and the drawbar length correction method were studied by simulation case studies and experimental works.