Diesel engines generally offer higher torque compared to gasoline engines. This allows for potential fuel economy improvements by using larger tires, sacrificing some initial acceleration. For instance, fitting the largest possible tires on a 1983 Mercedes-Benz 300D resulted in a higher actual speed compared to the indicated speed on the odometer. A freeway test showed an actual speed of 80 mph when the odometer read 65 mph—a 23% increase. This translates to a potential fuel economy increase from 28 mpg to 34 mpg.
Factors like slower acceleration should be considered. However, in the case of the 300D, the impact of larger tires on performance was minimal, especially with an automatic transmission due to the torque converter’s ability to compensate. A 1977 Mercedes-Benz 240D with slightly larger tires showed negligible performance difference.
Tire pressure and brand also influence fuel economy. Michelin tires generally provide better fuel efficiency compared to other brands like General tires. A 2 mpg loss was observed on an SUV when switching from Michelin to General tires of the same size. Researching tire rolling resistance is recommended for optimal fuel economy.
A 1977 240D consistently achieved over 30 mpg. A 1983 300D (turbo) delivered around 30 mpg on the highway. Fuel economy data for a 1981 240D was not recorded.
