I like to start with simple checks when dealing with any automotive issue. In the case of poor MPG, I like to start with the tire pressure. This is an often-overlooked item, and one that should be first on the list. Your tires are everything when it comes to your vehicle, and gas mileage is no exception. The rolling resistance of your vehicle has a direct effect on your fuel economy. If your tire pressures are low, your vehicle will have to work harder to get itself down the road. The harder your vehicle works, the more fuel it will use. It really is that simple.
The type of tire you use has a direct effect on fuel economy. Some tires are better than others; some have less rolling resistance. You might spend more for better tires, but in the end, you will likely come out on top based on your fuel savings alone.
As for what you should set the pressure at, check your owner’s manual or the tire sticker that should be located somewhere on your vehicle. There are a lot of places they put these things. Mostly I see them on door jambs, or sometimes on a sticker in the glove box. Occasionally I find them under the hood. The important thing is to find it and set your tires to that spec.
Many people make the mistake that the pressure indicated on the outside of the tire is where you want to set the pressure. This could not be further from the truth. That listing is the MAXIMUM tire pressure for that tire, NOT what you should set your tire pressures at. I also often see that people want to inflate their tires till they look round, with no bulge at the bottom. Once again, the wrong approach. That bulge at the bottom of the tire is important. It’s called the “foot” or “contact patch.” The name implies its purpose, and it is an important one. After all, you wouldn’t walk very well without your feet, or even feet that didn’t have the proper shape. Overinflated tires have the same effect. Plus, overinflated tires can be dangerous. Sure, you’ll get great fuel economy with overinflated tires, but the safety risk just isn’t worth it. Vehicles with overinflated tires are unstable and difficult to control. So please, don’t go by appearances when it comes to inflating your tires. Inflate them to the proper pressure and move on.
Here are some videos to reinforce what I’ve talked about here.