This car myth masqueraded for decades as an insider's tip for getting better gas mileage with less wear and tear on your tires. It does neither, according to Martin.

"You want to keep your tires at the recommended pressure because if they're over-inflated, they wear one way, under-inflated they wear another," says Martin.

"Try to get even wear and rotate your tires every 7,500 miles."

Duchene agrees.

"It doesn't make a whole lot of difference on mileage," says the Oregon-based automotive writer. "As far as wear goes, it's better than under-filling them, and the reason is, for every pound that a tire is under the recommended pressure, it will run hotter and wear faster.

"If you ran a tire five pounds under the recommendation, it would last probably 20 percent less."

-- Text by Jay MacDonald, illustrations by Brandy Kesl.