Granted, the cab-top 3D fairing or ‘spoiler’ has become the accepted thing to fit. It makes aerodynamic sense, and enhances the truck’s image.
However, carefully-monitored tests have shown, in one example, that a 3D fairing alone yielded a drag reduction of 26.8%, but when sidewings were added, this increased to 38.3%. If the fuel saving percentage at highway speed is potentially half of the drag reduction percentage, on this vehicle the fairing could yield 13.4% fuel saving at speed, and the sidewings could add another 5.75% fuel saving.
In a further case, Operator results showed fuel savings of 7% with a solo 3D fairing which increased to 9.5% by adding cab rear sidewings.
In summary, tests have shown that the addition of sidewings could potentially increase the fuel saving by a factor of 1.3 to 1.4.