A method for quantifying the resistances of light and heavy-duty vehicles under in-use conditions

Tyre rolling resistance and air drag significantly affect road-vehicle fuel and energy consumption. Their importance is recognised in vehicle certification regulations and standards worldwide. Detailed methodologies for their determination exist that require testing in dedicated proving grounds or specialised test facilities outside of actual driving conditions. As countries strive to improve vehicle efficiency, in-use verification of vehicle resistances will become essential for research and vehicle homologation. Multiple factors may limit such activities such as cost, lack of dedicated test infrastructure and equipment, and incompatibility with other vehicle-related tests that already take place. This study proposes a new method for determining vehicle resistances during on-road measurements based on wheel torque data. The method allows less expensive, more versatile test procedures that could be applied to a wide sample of vehicles across the fleet. The method was evaluated experimentally with nine vehicles (3 light-duty, 6 heavy-duty). Repeatability tests showed that the air drag error standard deviation ranged from 1 to 5.5 % for light-duties, and the pooled error standard deviation was 5.8 % among all heavy-duty vehicles. The results showed a divergence from the target cycle energy demand of <5 % during the on-road tests, a limit indicating the highest expected test discrepancy due to test uncertainties. Vehicle fuel consumption was simulated with both the measured and official resistance coefficients as a secondary validation. The on-road calculated coefficients led to accurate estimates of real-world consumption. The study discusses the impact of the wind vector during the test on the air drag and resistances' influence on consumption.