Can somebody tell me if lowering the tailgate on a truck actually improves gas mileage? I am quite perplexed.
Apparently not:
This isn’t going to be explained very well, and it was easier to understand when the folks on the NASCAR show used little animations of airflow, but I’ll try - and I’m sure I’ll get something wrong and be corrected by the next posters -
Mileage is best with the tailgate up. With the tailgate up, the air within the bed of the pickup remains as a sort of “bubble,” relatively motionless (which is why, generally, lightweight things placed in the bed of a pickup do not fly out with the wind). The airflow over the truck also flows relatively smoothly over the “bubble” as though the bubble were part of the truck. The air doesn’t “smash” into the tailgate, like you might expect.
Lower that tailgate, however, and your “bubble” gets burst - the air flowing over the truck can’t flow smoothly over the bed and out the back the way it did. It gets all roily in the bed.
Effectively, lowering the tailgate changes your truck from very nearly a rectangle - not that much difference in height between the roofline and the bedline - to a square with a very low, flat surface behind it, which is less aerodynamic and creates a lot more drag. Those “nets” that some people replace their tailgates with have the same effect.
Makes sense to me, although before I would have thought differently. Thanx! 