For at least 50 years, the interest in understanding and reducing the rolling resistance of pneumatic tyres has been growing. This interest is driven by the need to reduce vehicle fuel consumption and CO2-emissions, for environmental and economic reasons. The amount of rolling resistance generated depends on the vehicle type, tyre properties and operating conditions. The main objective of this literature review is to provide an overview of the most influential operating conditions with respect to rolling resistance, their effects and their connection to different measurement techniques. The examined operating conditions are the inflation pressure, the temperature, the curvature of the test surface, the load, road surface, speed, torque, slip angle and camber angle. In addition, the definition of rolling resistance is investigated, which shows lack of harmony in the literature. There are important areas where little research can be found and where further research would be valuable. Examples of such areas are effects of the torque, slip angle and camber angle on rolling resistance, thorough comparison between flat-surface and drum measurements, effects of temperature difference between laboratory measurements and actual driving on rolling resistance and evaluation of Unrau’s formula for temperature correction of rolling resistance measurements.

Measurement methods to determine the rolling resistance of tyres during different operation conditions are essential in the work towards more energy efficient vehicles. One of the influential parameters is the tyre temperature distribution, which has a large impact on the rolling resistance. Today, the standardised test procedure to measure rolling resistance is steady-state measurement on drums. However, the steady-state temperature on a drum is not the same as the temperature during ordinary driving conditions. The aim of this work is to develop a measuring method that enables to set a desired measurement temperature, which would create the possibility to study the relationship between tyre temperature and rolling resistance in more detail. The measurement method was developed by the use of a flat track equipment but should be applicable to other rolling resistance measurement equipment such as drums. The resulting method gives a repeatable tyre temperature and rolling resistance and can be used for measurements on tyres heated to a chosen measurement temperature. 

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 ⁰C 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 ⁰C to 35 ⁰C, was determined based on tyre temperature measurements on a car in traffic during springin 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 ⁰C. 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.

Rolling resistance has become one of the key parameters that the vehicle industry is focussing on in their efforts to make vehicles more energy-efficient. Rolling resistance is generally measured in steady-state on a test drum which results in a higher rolling resistance compared to flat track measurements for the same test settings due to the curvature of the drum which deforms the tyre more. Therefore, the drum steady-staterolling resistance is commonly converted with Clark’s formula, as suggested in the rolling resistance measurement standards. The accuracy of Clark’s formula has been questioned by Freudenmann et al who suggest an adjusted formula for steady-state measurements. The aim of this work is to compare drum and flat track measurements performed at the same inflation pressure and tyre temperature instead of at steadystate and investigate whether Clark’s or Freudenmann’s formula can be used to convert the drum measurement to a corresponding flat track level. Non-steady-state measurements have been performed on both test drum and flat track. As expected, Freudenmann’s formula is not good for the conversion at nonsteady-state settings, since it was empirically developed for steady-state. Clark’s formula works better for conversion of measurements performed at the same tyre temperature and inflation pressure compared to steady-state conversions reported in literature. However, the dependency of rolling resistance on temperature is not the same in the drum and flat track measurements, causing a difference between the results which increases as the tyre temperature decreases. Further research is needed to improve Clark’s formula by including the effects of tyre temperature

A rolling resistance model (RRM) has been created and parametrised with the purpose of modelling tyre rolling resistance within complete vehicle dynamics simulations. The RRM is based on a combination of the Masing and Zener models to simulate the Payne effect and the viscoelastic properties of rubber. The parametrised model is able to recreate the relationship between the rolling resistance and the tyre deformation well and it has a low computational power requirement. Today the model is limited to simulation of free-rolling tyres on a flat surface, but it can be extended to also include the effects of changes in operating conditions such as wheel angles or road surface.

The rolling resistance of car tires is one of the most important parameters characterizing tires today. This resistance has a very significant contribution to the energy consumption of wheeled vehicles. The climate crisis has forced tire and car manufacturers to place great emphasis on the environmental impact of their products. Paradoxically, the development of electric vehicles has led to an even greater importance of rolling resistance, because in electric vehicles a large part of the influence of grade resistance and inertial resistance has been eliminated due to re-generative braking, which resulted in rolling resistance and air resistance remain as the most important factors. What is more, electric and hybrid vehicles are usually heavier so the rolling resistance is increased accordingly. To optimize tires for rolling resistance, representative test methods must exist. Unfortunately, the current standards for measuring rolling resistance assume that tests are carried out in conditions that are far from real road conditions. This article compares the results of rolling resistance tests conducted in road conditions with the results of laboratory tests conducted on roadwheel facilities. The overview of results shows thatthe results of tests conducted in accordance with ISO and SAE standards on steel drums are very poorly correlated with more objective results of road tests. Significant differences occur both in the Coefficients of Rolling Resistance (CRR) and in the tire ranking. Only covering the drums with replicas of road surfaces leads to a significant improvement in the results obtained.For investigations of rolling resistance in non steady-state conditions, the flat track testing machine (TTF), equipped with asphalt cassettes, is shown to provide measurement data in agreement with the road test data.