Edmunds, publisher of automotive websites, tested various ways to increase gas mileage. Here’s their take on tire inflation:

Test #5: Check Your Tire Pressure No matter how many times drivers hear about the importance of tire pressure, most of them don’t do anything about it. They probably don’t like squatting beside their car in a busy gas station with fumes swirling around them. But is it important? The answer is yes, for a number of reasons. Properly inflated tires are less likely to fail at high speeds. They wear more evenly and, yes, they deliver better gas mileage. How much? In this test we saw a modest difference in two of the cars. It might have been more dramatic with different tires on different cars. Experts swear by it; we couldn’t really document it. And we wound up wondering if tire technology, like the design in other areas of the car, had improved. Eventually, we concluded that each set of tires is different and every vehicle is different. We recommend that you do your own tests to see what inflation setting gives you the best fuel economy. Method: We drove the 55-mile test loop four times at 60 mph — twice with tires at or above proper inflation. Once, we did the test with the tires 5 psi below the pressure recommended by the manufacturer. Since this produced very little difference we enlarged the gap and under inflated the tires by 8 psi. We felt that it was important to make sure the tires were inflated to the recommended level or above.

They do have other recomendations that make more sense, mainly, stop driving like Al Gore’s son.

I don’t doubt that there are some savings to be found by having properly inflated tires, but I think trying to extrapolate an average savings per car, then multiplying that figure by every car in America — which is what Obama, ABC and Politifact are doing — just doesn’t hold up that well.