[Christ]

If you exit the air in front of the tire, it's being propelled already by pressure, so the tire won't need to "cut through it." It will actually save the tire from cutting through anything, as the warm air circulating near the tire would create a smooth surface for the cooler flowing air to go over. At the same time, the warmer air will be forced backward by the flow around the front of the car, so it's like "excess" airflow that will actually help keep flow attached, I think.

Of course, I can't prove this without a wind tunnel, so it's just a theory.