Proper tire inflation is an important part of optimizing your vehicle for good gas mileage. Under inflated tires can cut your mileage by as much as 6 percent, according to some studies. Add to that 6 percent the one mile per gallon you lose when you operate your air conditioner and it's clear that you really want to check your tire pressure to increase gas mileage. Other ways to use your tires to increase mileage include driving steadily, with no jackrabbit starts or sudden braking. Fuel efficient tires are also an excellent way to improve gas mileage even more.