Time for a pop quiz.

1. When is the last time you checked the air pressure on every tire on your car?
2. When did you last check the air pressure on your spare?
3. What is the proper pressure to which your vehicle's tires should be kept inflated?
4. Is that number the "maximum psi" imprinted on each tire's sidewall, or should it be a different pressure?
5. Should you keep all four tires inflated to one pressure, or is it different for tires mounted on your front and rear wheels?
6. When did you last rotate your car's tires?
7. When did you last do a four-wheel alignment on your car?
8. Would your car's tires pass the "penny test" or the new "quarter test"?

OK, pencils down.

So how'd you do? Think you got all of the answers right? Did any of these questions stump you? Are you happy or unhappy about how you did?

The good news is that if you didn't do as well as you thought you should, this quiz will not earn you a letter-grade and you needn't worry about having "See me after class" scribbled in red ink on top of your answer sheet. But the bad news is that you'll be the one who'll be driving in your car later today -- either alone or with your friends or family.

The Rodney Dangerfield of auto components
"One of the most common things that we see at our service centers is that people are not maintaining proper tire pressure in their tires," says Matt Edmonds, vice president of Tire Rack, an independent tire tester and retailer of tires, wheels and performance accessories. "With today's radial tires, you can literally have a tire that's down in terms of pressure by up to 25 percent, yet, visually, that won't even be noticeable."

But based on the company's experience -- a team of drivers test tires from every major tire manufacturer on a state-of-the-art, 10-acre test facility at the company's headquarters in South Bend, Ind. -- when a tire is underinflated by a mere 10 percent, it is likely that it has suffered some degree of internal damage.

There's really no way to tell how much damage was done without dismounting that tire and looking inside, says Edmonds. "And if you did that, you'd likely find that the tire's inner liner has started to crumb and that an accumulation of rubber power has started building up inside of the tire.  When you reinflate such a tire, everything might look OK from the outside, but the damage has been done on the inside."

That is why the Rubber Manufacturers Association, or RMA, places such an emphasis on its consumer tire-education program, says Dan Zielinski, senior vice president of public affairs at the Washington, D.C.-based national trade association for the elastomer products industry. He says an easy-to-remember handy acronym -- PART -- explains the four essential elements of tire care: pressure, alignment, rotation and tread.

P is Pressure
Tire pressure is critical to tire safety and longevity. When a tire is properly inflated, you not only optimize your vehicle's safety but also save money at the gas pump, and you help make your tires last a whole lot longer. Drivers should check their tire pressure at least once a month with a quality tire gauge and ensure that every tire on their vehicle -- including the spare, if so equipped -- is properly inflated, says Zielinski. And it's best to check tire pressure "cold," early in the morning, before the car has been driven.