Measurement and Evaluation of Rolling Resistance of Car Tyres at Low Operating Temperatures

In the strive towards more energy efficient vehicles, efforts are made to reduce rolling resistance as one of the main resistive forces. Within the European Union (EU) tyres are labelled to guide consumers to choose a tyre with low rolling resistance. The tyres are labelled based on a standardised rolling resistance test performed at 25 ℃ on a test drum, where the tyre is run until it reaches steady-state conditions. However, due to the high ambient air temperature, steady-state conditions and the curved surface of the drum, the rolling resistance in a standardised test is commonly measured at a higher tyre temperature compared with many real driving situations. The overall aim with this work was to experimentally measure the rolling resistance at low operating temperatures on a flat surface, which better correlates to realistic operating conditions compared to the EU standard measurement method. The investigated tyre temperature range, 0 ℃ to 35 ℃, was determined based on tyre temperature measurements on a car in traffic during spring in Sweden. Rolling resistance measurements were performed on a flat track test equipment for four car tyres with the same dimensions but different rolling resistance labelling. For the tyre with the largest temperature influence, the rolling resistance increased by almost 80% for a temperature reduction of 20 ℃. These results emphasise the importance of the tyre temperature influence on rolling resistance. Further research is needed to conclude whether, and then how, the standardised measurements should be updated to address this temperature influence.