It’s no secret that your car’s tires, specifically the amount of air inside them, has a huge bearing on your fuel mileage. Under-inflated tires are one of the leading contributors to poor automotive fuel mileage in this country, just one reason the state of California now requires auto service facilities to check and record their customers’ tire pressures, a move the state hopes will save drivers millions in fuel costs with a resultant reduction in emissions.
Not only that, but when your tires have correct inflation pressure, you’ll experience better comfort on the road, your tires will last longer, they will grip the road better (keeping you safer), and your tires’ performance will match your vehicle’s handling dynamics just as the engineers that created it intended.
With that in mind, we’ve come up with 11 things you should know about checking your car’s tire pressure—and methods you can use to ensure they stay inflated! (Don’t know how or don’t want to check your tire’s air pressure? Stop by your favorite auto service facility, many of which will perform the service for free.)
1. Losing it.
It’s possible for a passenger car tire initially inflated to 35 psi (or “pounds per square inch”, a measure of tire inflation), to lose as much as one psi each month. If your car is equipped with a tire pressure monitoring system (TPMS), you’ll likely get an alert when the inflation drops below 30 psi.
2. Out in the cold.
For the most accurate reading, tire inflation pressure should be checked when a tire is cold. Inflation pressure tends to increase as the air inside tires warms up and expands when you drive down the road. (By the same token, that’s also the reason your car’s TPMS may indicate a low tire pressure on very cold mornings, then later blink off as the air inside the tires warms.)
3. Don’t forget the spare!
Whether your car has a full-size or mini spare tire, be sure to check its inflation pressure, as well.
4. Searching for info.
You’ll find the recommended air pressure for your factory tires at one of the following places:
• In the vehicle owners manual.
• On the vehicle’s door jamb. (Often, a vehicle information placard is located on the door jamb along with the recommended tire inflation pressure.)
• Inside the fuel hatch filler flap. (In some vehicles.)
• The glove compartment door. (In some vehicles.)
5. The wrong place.
You will NOT find your vehicle’s recommended air pressure on the tire. Inflation pressure printed on tire sidewalls is only the maximum tire pressure. Use the recommended tire inflation pressure for your vehicle.
6. Gauging success.
Air pressure gauges at gas stations are okay for use in a pinch (just a look at one and you can see it’s probably been through a tough life), but tire experts recommend purchasing a good pressure gauge for yourself.
7. Valves are valuable.
Those tiny valve caps may seem trivial, but their importance cannot be overstated. Not only do they keep out dust and debris (ever seen a piece of gravel stuck in a valve lead to a flat tire?) and protect the valve core, they also keep moisture from entering the tire, which can lead to corrosion or even valve core damage if the moisture freezes.
8. Inflation is important—and efficient.
According to the U.S. Department of Transportation, under-inflated tires can lower gas mileage by 0.3 percent for every one psi drip in pressure of all four tires. Overall, gas mileage can be increased by 3.3 percent by keeping tires inflated to proper pressure. That may not sound like much, but it’s like saving 9 cents per gallon of gas at the pump, and who among us wouldn’t drive across the street for that kind of savings?
9. Mind your TPMS.
If your car is equipped with a TPMS—and it’s a requirement for every car sold in the country since 2007—you’ll need to pay special attention to tire maintenance. Most tire pressure monitoring systems use remote pressure sensors coupled with radio-frequency transmitters to send tire pressure data to the car’s onboard computer. Some automakers use systems that are wheel-specific (i.e. each transmitter corresponds to a certain wheel, like right-front, left-rear, etc.). If your tires are rotated or otherwise serviced, the TPMS will have to be recalibrated or reprogrammed to reflect the change. Make sure your auto service provider can perform this task before having your tires rotated or repaired.
10. Getting your fill.
Racecar drivers know a thing or two about the importance of tire pressure, which is why many racing teams have been using nitrogen to fill tires for years (along with airlines and military vehicles). Using pure nitrogen (as opposed to compressed air, which is 22 percent oxygen, carbon dioxide and other trace gases) tends to keep tires inflated better and longer, as nitrogen molecules, which are larger than oxygen molecules, don’t slip through the rubber in tires as easily. (In fact, according to the experts, oxygen molecules escape about three to four times faster than nitrogen.) Not only that, but without oxygen, which is a highly corrosive element (hence the word “oxidation”), tires usually last longer, as well.
You might have noticed more new cars being sold with green valve caps, too. That’s because automakers and dealerships are increasingly getting on the nitrogen bandwagon. Ask your auto service technician about nitrogen tire inflation. There is usually a charge involved (for the cost involved with mechanically extracting pure nitrogen from air), but the benefits are tangible.
11. Know when to change.
Like most things, even the sturdiest of tires have a finite lifespan. You can extend that lifespan by keeping your tires properly inflated, but how do you know when to change them? Simple—use the penny test.
Take a standard penny and insert it upside down into the tire tread (i.e. Honest Abe’s head should be inside the tread). If you can see the top of Lincoln’s head, it’s time for new tires. Why? Because the tread has worn to the point where the channels that move water out from between the tire and the road can no longer function effectively, meaning you’re at greater risk of losing control in wet, icy or slippery conditions.
Your tires provide the only connection your car has with the road. Making sure they are properly inflated can go a long way to making your car more efficient and keeping you safe on the road.