Using a Cargo Box on Top of a Vehicle Can Reduce Fuel Economy by 25%

While traveling for vacation, adding a cargo box on top of a vehicle can decrease fuel economy significantly compared to using a rear cargo tray. Testing was performed on two vehicles – a 2009 Toyota Corolla and a 2009 Ford Explorer with no cargo, with 100 lbs. of cargo in a cargo box on top, and with 100 lbs. of cargo on a tray at the rear of the vehicle. At 65 miles per hour (mph), the cargo box on top of the Toyota Corolla resulted in a decrease in fuel economy of 25%, but the cargo tray produced only a 1% decrease. The Ford Explorer’s fuel economy at 65 mph decreased by 10% with the cargo box on top, but by only 1% when using the cargo tray. The fuel economy decrease varies with the speed of the vehicle.