The most important safety feature on your car isn’t its airbag or even the seat belts—it’s the tires. This should be obvious; those four round black things are the only part of the vehicle to actually touch the road, after all. Sadly, most American drivers fail to take care of their tires, with 35 percent of drivers not able to tell if their tires are bald. When you consider that the National Highway Traffic Safety Administration found that vehicles with worn out tires were three times more likely to end up in a crash, you can see the problem.

That data is from a 2015 survey conducted by the US Tire Manufacturers Association (USTMA), which held its annual National Tire Safety Week in May. "[The Tire Safety Week] was born as a way to allow us to talk about tire safety to consumers," Kimberly Kleine, USTMA's vice president of public affairs, told me recently. The trade group has been running the program since 2001 to promote consumer awareness about checking tire pressure, suspension alignment, and tread depth, as well as the need to rotate tires.

When we spoke, Kleine and her colleague Tracey Norberg, senior VP and general counsel at USTMA, shared some other scary statistics. In addition to so few people knowing when their tires are out, 40 percent think they can tell if a tire is under-inflated just by looking at it. And just 17 percent knew how to check their tire pressures. You'd think that in the age of government-mandated tire pressure monitoring systems (TPMS), this would be a thing of the past. Not so. "Even if a car has TPMS, the warning light will only go on once a tire is 25 percent below its recommended pressure," Norberg explained.

By that point, you really do have a problem, as a recent late-night cab ride home from the airport proved to me all too well. At first I thought my driver's car was about to suffer an imminent suspension failure as it shimmied and yawed over every bump in the road; then I noticed the illuminated TPMS warning light on the dash.

"Handling problems from under-inflated tires are often mistaken for broken suspension," Kleine told me.

Beware of unsafe used tires

The focus of this year's tire safety campaign has been targeting the problem of unsafe used tires. "We're not talking about retreaded tires," Norberg told me. "In the commercial tire market, retreaded tires account for half of all truck tires. The retreading is done to professional certifications and allows them to last much longer than a new tire would." The problem here is with used tires for cars or light trucks, which are taken off other cars when they're worn out and then resold to other drivers rather than being taken to the scrapyard or spending the rest of their life as part of a barrier at a race track. "We've seen tires that are worn out with 2/32" of tread or less, with the steel belts exposed, with damage to the inner liner, or tires that hadn't been resealed" Norberg said. "One we displayed had a visible tack in it."

It turns out there's no legal standard in the US for used tires, so the process of collecting and inspecting them varies widely. "Some do it responsibly and stand by their product, but some don't," Kleine said. Some states like New Jersey and Colorado have passed legislation to prevent the sale of unsafe used tires, and USTMA is working with lawmakers in Ohio to pass something similar.

Check your rubber regularly

So consider this something of a PSA, in the same vein as our recent feature on the benefit of winter tires. Per USTMA's recommendations, you should check your tire pressures every month, and you should do it when the tires are cold. If you do need to drive somewhere to check your pressure, remember that Boyle's Law means the gases will expand as they get hot, which means the hot tire pressure will be three or four PSI higher as a result. And have a look at your tread depth while you're at it; below 2/32" and you need new rubber. (This is easy to check with a coin.)

It's also wise to have your vehicle's alignment checked once a year—too much camber or toe can cause uneven wear, not to mention handling problems and worse fuel mileage. And while you're having that done, it's a good idea to have your tires rotated.

Interestingly, USTMA doesn't have an official recommendation on aging tires. "Our member companies have recommendations, and car companies have recommendations," Kleine said. "We feel it's more important for a tire to be regularly inspected and maintained." If you're unsure of what to look for with your tires, she recommended taking them to a local tire shop. "Most if not all tire service retail stores will inspect them for free and typically inflate them for free, too," she told me.

Be safe out there, people.