Whether you know it or not, driving a car is probably one of the riskiest things you’ll ever do. Substantially increasing that risk is the prospect of worn-down, bald tires with little to no tread. Unfortunately, a worrisome segment of the driving population can’t tell a normal tire from a bald one.

According to the US Tire Manufacturers Association (USTMA), 35 percent of American drivers can’t tell if a tire is bald. In addition, 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 pressure. These statistics are from a 2015 study, which resurfaced during National Tire Safety Week earlier this month in Ars Technica.

Vehicles with worn-out tires are three times more likely to end up in a crash, according to the National Highway Traffic Safety Administration (NHTSA).

This study showed that tire-related crashes were more likely as your tire’s tread wears, with accident rates at just 2.4 percent when tires had near full tread depth to 26 percent when the tires were worn-out (0 - 2 /32” depth). We recommend consumers start shopping for new tires at 4/32” tread depth while some all-weather grip is still available. At this point tire-related crashes approached 8 percent.

“Properly checking and inflating your tires is an important step to help make your tires last longer, save you money and protect you and your family on the road,” NHTSA says in an advisory that was released on Thursday. The agency recommends checking your tire pressure and tread at least once a month.

Tires have built-in “treadwear indicators,” which are raised sections that run in between the tire’s tread. When the tread is worn down so that it’s level with the tread indicator, it’s time to replace your tires. You can also easily test your tire’s treads with any coin you have handy.