Did you know that how much air you have in your tires can have a direct affect on your gas mileage? It’s true, and it’s very easy to check on your own. Here are some common questions we hear and things you should know about extending the life of your tires and getting the most mileage out of every gallon of gas.

Why is tire pressure important to gas mileage?

A lot of folks are surprised to learn that underinflated tires can reduce the gas mileage for their vehicle. But think of it this way. Let’s say you have a sack of cement you need to move, and you have two items you can use to haul that sack of cement across a concrete driveway. One is a four-wheeled wagon, and the other is a toboggan. With the wagon, each of the four wheels has a small portion touching the driveway. Let’s say it’s one square inch per wheel. So there’s a total of four square inches in contact with the driveway. That wagon will roll along pretty easily with that sack of cement.

But now imagine the toboggan. It may have up to six square feet of surface in contact with the driveway, and that will make dragging that sack of cement very difficult.

Your tires are just like that. When properly inflated – let’s say at 35 psi, or pounds per square inch – each tire might have four square inches of surface in contact with the road. But if those tires are underinflated, what happens? They flatten out, and when they do that, more tire surface is now in contact with the road. It could be eight square inches now, and that adds more friction between the road surface and the tires while you’re driving. That causes your engine to work harder. As a result, your gas mileage declines.

Does that mean overinflated tires will improve my gas mileage even more because the tire surface on the road gets even smaller?

It doesn’t quite work that way. The correct tire pressure also insures that the tire is evenly in contact with the road across the entire tread. Both over-inflating and under-inflating can lead to uneven tire wear, which reduces the life span of your tires. When your tires are under-inflated, besides creating more friction, the center area of the tread can bulge upward off the road surface, leading to the outside edges of your tires showing more wear more quickly. And when your tires are over inflated, the tire bulges outward, causing the middle of the tread to wear more quickly than the edges.

So how much gas can I really save by just keeping the tires inflated properly?

Believe it or not, you can get another three to four miles out of every gallon of gas just by making sure your tires are inflated properly. For most cars, that’s like getting another 36 miles out of every tank full! If you fill your tank on an average of once per week, then you’re gaining an additional 1,872 free miles in a year! At today’s price of gas, that’s worth paying attention to.