Brake cooling is the only thing that comes to mind. Some truck owners “cover” front & rear on trailer tires, but this is mainly to keep the trailer clean. Same with some aftermarket fender designs for the tractor drive axles.
The 579 Peterbilt I’m in has the FE-conscious EPIQ package. And (brand) FLOW BELOW tractor drive axle package.
Stock, the tractor features Texas Flyswatter mudflaps. But conventional polished steel front quarter fenders.
Now, the Steer Tires have terrific enclosure. No spats, per se. Embiggen the pics. The tire enclosure extends from fender inwards to tire. A very very small gap remains.
Air is prevented from getting underneath the tractor. Essentially.
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