New Parameters for Comparing Tire Rolling Resistance

One of the objectives of laboratory measurements of tire rolling resistance is to compare tires. This requires that a common basis be established for this comparison. For tests performed per the current standard, SAE J1269, rolling resistance measured at a standard load/pressure condition, at 80 kph, is used for this purpose. However, a similar specification should not be used for rolling resistance measured as per the new standard under development, SAE J2452, because the data are collected at multiple speeds for each load/pressure condition. This paper explores alternatives, defines new parameters and proposes a new methodology for comparing tires using data generated as per J2452. The new parameters are MERF (Mean Equivalent Rolling Force) and SMERF (Standard Mean Equivalent Rolling Force). The mathematical derivation of these terms is presented and their use illustrated using laboratory rolling resistance data generated as per J2452. In addition to comparing tires, the proposed approach could also have other possible applications, such as specifying tire design targets that are more representative of the relative contribution of tires to the fuel consumption of a vehicle driven over a standard urban/highway cycle.