Efforts are currently made both in europe and usa to standardize methods for measurement of noise from the interaction between tires and the road. In this work it has been considered, as one major alternative, to use a hybrid of the so-called coast-by and trailer methods. This hybrid is here called the trailer coast-by method. Instead of using a truck fully equipped with the tires to be tested, the test vehicle consists of a single-axle trailer towed by a truck via an exceptionally long towing beam. The test tires are mounted on the single-axle trailer. Special measures are undertaken in order to minimize noise from all other sources than the test tires. During the measurement, the truck and trailer are coasted down and trailer are coasted down the measuring track and the peak noise levels in a microphone located on the test track, 7.5 or 15 m from the center of travel, are read. In this report, the authors investigate the advantages and disadvantages of this method by using a simulation program which makes possible plotting of noise levels versus time ("time histories"), for various input data. From these time history simulations, the separation of the noise from the towing truck (which is unwanted) and the noise from the test tires (which is "wanted") is studied. Different scenarios are shown to give different influences from towing truck noise on the measured result. Based on the simulation study, recommendations are given as to the design of the method for optimization of its accuracy. However, the main conclusion is that the method does not offer any major advantage over the cost-by method but has several disadvantages. (A)
Abstract