But you are still finding that something is robbing you of the fuel economy your should be showing... Tires!
If your car does not roll smoothly on properly inflated tires you will lose mileage.
I found that out the hard way:
Last spring I drove all the way from Upstate New York down to Florida on tires that were under inflated by about 7 lbs. I was getting lousy mileage. And I was even using a fuel additive.
I wasn't paying attention to the tires until one of the vacation days I noticed the front tires were showing unusual wear on the outsides. I did not carry a tire gauge, so I could not check to see what the tire pressure was at that time.
I noticed that there is a Honda dealership near the condo we were staying at. I dropped in at the chance that someone would be able to look at my tires.
The service coordinator had some time and was able to check the tire pressure for me. He found them to be at 29-30 lbs. He told me the pressure in the tire should be at 35 lbs.
Man, the tires were grossly under inflated. Thank God he was able to add air up to the proper pressure at no cost. Of course the damage had already been done to the outside of my tires. He even recommended replacing them. I was not ready to do that being away on vacation. I ended up rotating the tires front to back and drove home without incident.
We actually drove home with properly inflated tires and got the mileage we were accustomed to when cruising on the highways.
I now regularly check the tire pressure in both our vehicles, so I know they will not be the "bad mileage" culprits.
To see how much air to put in your car's tires you can check inside the door jam or your vehicle's Car Manual. This will give you the factory recommended tire pressure for your vehicle.
To check the pressure, I use a digital tire gauge, as I had misplaced my old pressure gauge. Both versions work fine. I did manage to find the analog gauge for this picture.
To inflate the tires I use a little portable air compressor. This way I don't have to pay 75 cents for something that should be free. I also do not have to look for an air station as not all gas stations have one.
This shows you that you can't exclude tire pressure from regular maintenance checks.
I won't make that same mistake again.