According to CarCare.org, underinflated tires can reduce gas mileage by 0.4% for every 1 PSI below the recommended maximum in all four tires. Even more amazing, a car tire can be 10 PSI or more under this recommended maximum and not appear low at all with visual inspection, reducing your gas mileage by 4%. Over a year, keeping your tires properly inflated can save $40 even on a car with good gas mileage (10,000 miles driven in a 20 MPG car with gas costing $2 per gallon). If you drive more, or your auto gets worse mileage, you can save substantially more.
Even better, keeping your tires at the proper inflation reduces wear on your tires, thus extending their life, and also reduces the risk of a blowout. Though this savings is a bit more intangible, it will save you money over the long run.
The procedure for airing up your tires is very easy and can be done for free at most gas stations. The only thing you’ll need is an air gauge, which you can borrow from the front counter at many stations (though I found it easier to just start keeping one in my own glove box).
Here’s what you do:
1. Look inside the door jamb of your car for a sticker. It should tell you the recommended maximum pressure for tires on your automobile.
2. Let the tires cool before checking their pressure. In other words, if you go to the station to do this, go to one near your home shortly after starting to drive after letting your automobile sit overnight.
3. Remove the cap from the valve on one tire. The valve is pretty obvious – it sticks out and has a little cap on the end that you can easily twist off. Put the cap somewhere where you won’t lose it (I lost one the first time I did it).
4. Push the tire gauge hard onto the valve. If you hear hissing, pull it off and try again, because that means you’re leaking air. You want to line them up straight and push firmly.
5. Add air to the tire. Take the air hose, press it onto the valve in much the same way as the gauge, and push about half a second for each PSI your tire was under the recommended maximum. Check the pressure again and add more if you need to using this rule of thumb.
6. Replace the valve cap.
7. Repeat steps three through six for all of your car tires.
You can also use this opportunity to check the wear on your tire. Jam a penny with the head out into the tread; if you can see any of Lincoln’s head, you might want to think about getting new tires.
How often should I do this? You should do it monthly during warm months and maybe once every two weeks in cold weather. I do it about every other fill up in the winter and about every third or fourth one in the summer.