Evaluation of fuel efficiency improvements in the HDV sector from improved trailer and tire designs

The ICCT and Verband der Automobilindustrie (VDA) commissioned the Institute for Internal Combustion Engines and Thermodynamics of the Graz University of Technology (TU Graz) to carry out tests of fuel efficiency improvements in the heavy-duty vehicle (HDV) sector from improved trailer and tire designs by application of a new test procedure developed for the European Commission Directorate-General for Climate Action (DG CLIMA).

Physical testing of vehicles on a closed track is a useful method for measuring drag forces resulting from air resistance and adhesion between the tires and the road surface. Two methods of assessing total drag were implemented: coastdown testing and constant-speed testing. To our knowledge, this project was the first time that coastdown and constant-speed tests with truck/trailer combinations were performed to investigate the repeatability and reproducibility of the two different test methods for determining tire rolling resistance and air drag resistance.

There are inherent difficulties in track testing, such as ambient wind speed, road-surface conditions, and determining the appropriate setup for data-measurement devices. Despite these methodological challenges, the testing project shows that there are quantifiable benefits of optimizing trailers for fuel-efficiency performance. Overall, the test results give evidence that employing low rolling resistance tires, aerodynamic side fairings, and weight reduction can lower fuel consumption on the order 4% to 10%, depending on the test method and ambient conditions. Variability in the results suggests that further refinement of the test procedures for both constant-speed and coastdown testing is required before either method can be used to determine aerodynamic or rolling resistance drag coefficients for use in a GHG simulation model that would be used for certification or type approval.

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