How G+P contributed to the improved accuracy of CPX measurements

Measurements involving rubber tyres can be a delicate matter as it is well known that over time the physical properties of rubber undergo significant changes. This is why one would like to normalize measurements to a reference rubber hardness. The recently published technical specification defining the reference tyres for CPX measurements (ISO/TS 11819-3), therefore, includes a new correction for tyre rubber hardness. Early experiences with this new correction procedure raised questions about its accuracy. The paper takes an in-depth look on the influence of tyre rubber hardness on CPX measurements for both reference tyres P1 and H1. Together with researchers from the Gdanks University of Technology and the Swedish National Road and Transport Research Institute (VTI) existing and new data were analysed. The paper, moreover, summarizes the research from several scientific contributions on this topic. It provides evidence that the effect of rubber hardness is tyre specific and that separate correction factors for the P1 and the H1 tyres lead to accuracy gains and improved repeatability and reproducibility of the method. The study concludes by proposing a revised tyre-specific approach for the tyre rubber hardness correction of CPX measurement results.

Since 2011 G+P contributed 7 papers aimed at improving the repeatability and reproducibility of the CPX-measurement method:

1. Bühlmann E, Ziegler T. Temperature effects on tyre / road noise measurements . Proc INTER-NOISE 2011, Osaka, Japan (2011).
2. Bühlmann E, Ziegler T. Temperature effects on tyre / road noise measurements and the main reasons for their variation. Proc INTER-NOISE 2013, Innsbruck, Austria. (2013).
3. Bühlmann E, Schulze S, Ziegler T. Ageing of the new CPX reference tyres during a measurement season. Proc INTER-NOISE 2013, Innsbruck, Austria (2013).
4. Bühlmann, E. & van Blokland, G., “Temperature effects on tyre/road-noise – A review of empirical research”, Proc of Forum Acusticum, Cracow, Poland (2014).
5. Bühlmann, Erik; Sandberg, Ulf; Mioduszewski, Piotr, “Speed dependency of temperature effects on road traffic noise”, Proc. of Inter-Noise 2015, San Francisco, CA, USA (2015).
6. Sandberg U, Bühlmann E, Conter M, Mioduszewski P, Wehr R. Improving the CPX method by specifying reference tyres and including corrections for rubber hardness and temperature. Proc INTER-NOISE 2016, Hamburg, Germany (2016).
7. Bühlmann E, S. Egger, P. Mioduszewski, U. Sandberg: An in-depth look at the tyre rubber hardness influence on tyre/road noise measurements. Proc INTER-NOISE 2018, Chicago, USA.