Do you get better gas mileage when you leave the tailgate of a pickup truck down?

Do you get better gas mileage when you leave the tailgate of a pickup truck down?: "With petrol
at an unholy premium, folks are willing to try just about anything to
squeeze a few extra miles between fill-ups. Many pickup owners have
long believed that lowering the tailgate cuts down on wind resistance,
and, as a result, saves gas. Seems logical, right?"

While many have tried this method, only a few have bothered to quantify the results. One driver went so far as to use a device called a ScanGauge that determines mileage in real time. As he puts it, his results were "surprising." He achieved 17.6 MPG with the tailgate up and 17.7 MPG with the tailgate down. A slight improvement, but 0.1 MPG doesn't exactly equal big savings at the pump.

Automotive experts Tom and Ray Magliozzi have an opinion too. Like most of us, they initially believed that an open tailgate improves wind resistance. But as it turns out, it simply isn't true. Aerodynamics engineers have found that wind resistance is actually lower when the tailgate is up. Why? When the tailgate is raised, a "separated bubble" of stagnant air is formed in the bed of the pickup. Wind tends to swoosh over this bubble as though it were part of the truck. Lower the tailgate, and the bubble disappears, which leads to increased wind resistance.

Looks like if you really want to save money on gas, your best bet is taking the bus.