Chassis dynamometer tests are often used to determine vehicle fuel economy (FE). Since the entire vehicle is used, these methods are generally accepted to be more representative of ‘real-world’ conditions than engine dynamometer tests or small-scale bench tests. Unfortunately, evaluating vehicle fuel economy via this means introduces significant variability that can readily be mitigated with engine dynamometer and bench tests.Recently, improvements to controls and procedures have led to drastically improved test precision in chassis dynamometer testing. Described herein are chassis dynamometer results from five fully formulated engine oils (utilizing improved testing protocols on the Federal Test Procedure (FTP-75) and Highway Fuel Economy Test (HwFET) cycles) which not only show statistically significant FE changes across viscosity grades but also meaningful FE differentiation within a viscosity grade where additive systems have been modified. Demonstration of statistically significant differentiation of fuel economy within a viscosity grade is a result of both robust additive technology and high test precision. Furthermore, the work demonstrates that with the specific vehicle and test cycle used, it is possible to obtain the fuel economy performance level of a 0W-16 with a 5W-30 containing a proprietary organic friction modifier (FM).