The Yokohama Rubber Co Ltd announced a "fin tire," an auto tire that has fin-shaped protrusions on the inner side (the side facing the other tire).
Though the air resistance of the fin tire itself is higher than that of a normal tire without fins, it can reduce the air resistance of an entire vehicle.
The Yokohama Rubber clarified the mechanism of the effect. According to the announcement, the pressure distribution in the tire house (inside the fender) is changed by the spirally flowing air that the fins generate in the rotation direction of the tire. As a result, a force is generated to help the vehicle move forward.
When a vehicle is running, air is randomly flowing in the tire house. And part of the air flows out to the lateral sides of the vehicle, increasing the air resistance of the entire vehicle.
The Yokohama Rubber has been engaged in a research to solve this problem. And, in 2010, it developed a technology for simulating air flowing around a tire on the assumption that the vehicle is actually running (and the tire is rotating in the tire house).
Since then, the company extended the range of the simulation to an entire vehicle and started to conduct wind tunnel tests. The latest development was based on the results of those efforts.