Where the Rubber Meets the Road
What do you need to know about buying new tires for your car?
I drive a 1992 Honda Accord, mostly within that hazy zone that is the speed limit. I don't corner aggressively or attempt 180-degree emergency-brake power-spins. So, what am I looking for in a tire? I want something that's reliable and worth the money I paid for it.
To get a tire education, I grilled a few auto mechanics and pored over informational Web sites. Then I went to a real expert, Daanesh Chanduwadia, who develops training materials for automotive dealer technicians. Daanesh used to manage a shop specializing in performance enhancements for European automobiles, and he says he has read and studied everything car-related he could find since 1984. But all this is more than you want to plow through, so below are the essentials—what you need to know.
When To Replace Your Tires
Daanesh begs you to accept the fact that your tires are disposable. They work right for a while, but then the longer you wait, the worse they perform. So have them checked often. If your mechanic says it's time, do listen, because worn-out tires ain't worth squat in the rain. A rule of thumb: If you can stick a penny edgewise into the grooves and still see all of Abe Lincoln's head, your tread is worn down to a thickness of 2/32 of an inch, and your tires are illegal in most states. You should replace well before you reach this stage. Your tire's performance is heavily compromised at this point, and the tire won't pass inspection.
All-Season or Summer?
Once you know that your rubber needs to go, it's time for another decision: all-season or summer tires? It's a crucial choice. Performance on snow and on dry pavement are two conflicting goals (almost mutually exclusive) and require very different tire designs. So, if you never ever see snow where you live, get summer tires—they'll handle better. But if you do drive on snow, even occasionally, get all-season tires. You need their treads if you want to get traction and lead a safe and productive life.
You do sacrifice a little with all-seasons. They aren't as impressive on dry pavement, though they still do fine. In a perfect world, you'd switch tires twice a year to fit the weather, but I'm assuming you're lazy and cheap like me and thus won't even consider this, and hey, that's cool—I'm not judging you.
(By the way, if you drive through thick snow all the time, you need real snow tires, not just all-seasons. But hearty souls like you already knew that.)
Reading a Tire If this is a newish car getting its first tire change, you'll be removing the "original equipment" tires—the ones the manufacturer put on. can help you decide which new tires to buy. Regardless, you should learn how to read a tire.
On your tire's sidewalls, you'll see lots of markings. One of them refers to size. On my Accord, the O.E. tires were marked "185/70-14": 185 is the width of the tread in millimeters; 70 is the "aspect ratio" of sidewall height (measuring the edge of the rim to the road) to that width; and 14 is the diameter of the wheel (equal to the hole in the center of the tire) in inches. The format is the same on most tires. You don't need to remember what the numbers mean, but you want to stick with the tire size you have. You can look up O.E. size for your own car (make, model, and year) on the fantastic TireRack.com.
Next, look at the speed rating on your old tires also stamped into the sidewall. This is basically the tire's maximum speed, but also hints at its total performance. Common examples include SR (112 mph), TR (118 mph), and HR (130 mph). You want a speed rating as high as or higher than the one on your O.E. tires.
I know what you're saying: "Jeepers, I never go over 70!" No matter. Cars designs rely on a certain level of tire quality, so if you swap in something lame it can be dangerous. Also, a high-speed rating gives you wiggle room. Says Daanesh: "If you do something boneheaded in a corner but it's only half of what your tire can handle, you're fine. If it's 99 percent of what your tire can handle, who knows …" Higher rated tires are stiffer, so they're tough to blow out in a pothole, but they make the car's ride a bit harsher. And they don't last as long.
Seth Stevenson is a frequent contributor to Slate. He is the author of Grounded: A Down to Earth Journey Around the World.