Myth: Overinflating your tires saves gas (and other misconceptions about fuel economy).

Facts:  Underinflated tires waste gas because a lot of tread meets the pavement and increases friction, while the reduced tread contact of properly inflated tires results in less fuel consumption. So you might think that overinflating your tires would get you even better mileage. But in 2006 Popular Mechanics magazine tested that theory and determined that no gas is saved—and you get a rougher ride.

Here are two other strategies to save gas that have been made obsolete by technology:

1. It’s better to let a car idle than to turn the ignition off and back on. That was probably true before modern fuel injection, but now starting your engine wastes no gas.

2. Keep your tank full because low levels of gas allow more evaporation. The way modern tanks are sealed makes that impossible, although it’s still important to tighten your gas cap.