Myth #4: Always over-fill your tires.
This car myth masqueraded for decades as an insider’s tip for getting better gas mileage and less wear on the tires. To be honest, this myth does not influence mileage. You should keep your tires at the recommended pressure because they wear badly when either over-inflated or under-inflated.
For best results, get even wear by rotating your tires every 7,500 miles. As for under-filling tires, for every pound a tire is below recommended pressure, it will run hotter and wear faster. If you ran a tire only five pounds too low, the tire’s life expectancy would be reduced 20 percent.