The challenging measurement of acoustic effect of road surface on truck tyre noise by standard close proximity method

The CPX method is an efficient tool for assessing and comparing road surface acoustic properties. For heavy trucks, the standard method ISO 11819-2 requires that noise measurements are also performed with a "pick-up" type of tyre with noise emission characteristics of heavy goods vehicles, and proposes the tyre "H1". However this tyre does not comply with European regulations since November 2016. The objective of this experiment is to test the Standard Reference Test Tyre SRTT-C2 for light trucks as a replacement. To this end, our CPX trailer was adapted to the large size of the test tyre. Then, the relevance of the SRTT-C2 to characterize road surfaces acoustically has been demonstrated in previous papers. The current paper presents a complementary study of the representativeness of this tyre, by comparing spectral effect on different pavements between CPX measurements with the SRTT-C2 tyre and SPB measurements of real trucks in the traffic. Combined SPB and CPX measurements were performed on three road sites, completed by CPB measurements to characterize the transfer function SPB/CPX. The results show that the SRTT-C2 tyre has a different spectral behaviour from that of heavy trucks (regardless of the number of axles) particularly in low frequencies.