There are a lot of numbers and millimeters that people throw around when it comes to how much depth you should have to your tire treads, it’s really confusing. It’s supposed to be easier now because in the U.S., tire manufacturers are required to have “wear bars” molded into them to make it easy to see when tire replacement is legally required. But that doesn’t seem to be helping, because we’ve seen plenty of cars come in with those wear bars right out there, plain as day, and the owner still has no idea they need new tires! So – states require tires to be replaced when the tread has worn down to 1/16 of an inch – or 1/5 mm. What does this mean in English? It means this: take a penny, and stick the top of Lincoln’s head straight down into the tread. If you can see most of his head and some of his hair, you’re taking your life in your hands, do not pass go, go get new tires! If the top of the Lincoln Memorial is covered, you’re ready for winter driving!