Tag: Five things to know about tires

You’re ignoring the most important part of your car: Five things to know about tires – Kurt Ernst @Hemmings

You’re ignoring the most important part of your car: Five things to know about tires – Kurt Ernst @Hemmings


Tires are the Rodney Dangerfield of car parts: They can’t get any respect. On the daily driver, they’re likely to be ignored until one goes flat, and on the project car, they’re likely to be the last thing in line for an upgrade. Yet those in the know understand that tire technology has advanced by leaps and bounds over the past two or three decades, and for those seeking improved performance, tires may offer the biggest single bang for the buck out there.

Consider this: Tires control how much torque you can translate into forward motion, how much speed you can carry into a corner, and how quickly you can scrub off speed. Don’t believe us? Borrow the keys to a Challenger Hellcat or equivalent and see how difficult it is to get a good launch on street tires. Sure, 700-plus horsepower sounds impressive, but if the car (or driver) has a hard time getting that to the ground, it’s just a number.

Admittedly, other components play a part, too, but tires are far easier—and likely less expensive—to upgrade than engines, transmissions, suspensions, and brakes. They’re also wear items that need to be monitored closely throughout their lifespan, especially if your car sees the occasional track day. Or, if you live in parts of the country where rain, cold temperatures, snow, and ice are harsh realities for part of the year.Below are five things to consider when shopping for a new set of rubber, whether it’s for your daily driver or a weekend toy.

To many, the codes on a passenger car tire’s sidewall might as well be Egyptian hieroglyphics, but with a little bit of information, they’re not mystifying at all. Here, we’ll focus on passenger car radial tire size, which is typically a sequence of three numbers followed by a forward slash, two more numbers, a letter or two, then two more numbers, a space, two numbers and a letter (like 205/55R16 91W).

The first number in the example above, 205, is the section width as measured in millimeters across the tread from sidewall to sidewall: This tire is 205 mm, or 8.07 inches, wide. Next comes the number after the forward slash, or in this case 55. This is called the aspect ratio, and it is a measurement of the sidewall height, expressed as a percentage of the tread width. Doing a bit of math, 55 percent of 205 mm works out to be 112.75 mm, or 4.44 inches.

Now, we get into the letters (or letter) following the aspect ratio. Tires made after 1991 typically have one letter, “R,” denoting radial construction. The exception is “ZR,” which indicates a “Z” speed rating of “in excess of” 149 mph. The adjacent numbers indicate the diameter of the wheel (16 inches, in our example above).

Modern tires also include a load index and speed rating (or clarification). The 91 cited in our example means that the tire will safely carry a weight of 615 kilograms, or 1,356 pounds. It’s most relevant as a baseline; when replacing passenger car tires, it’s okay to go with ones carrying a higher load rating, but not ones rated below the manufacturer’s specified load rating. Finally, the “W” indicates the tire’s speed rating, in this case up to 168 mph. (This can also be displayed with a “ZR” next to the aspect ratio, clarifying the maximum speed of the tire instead of just a range.) Listing all service ratings and speed ratings would fill most of a page, but this information is readily available online.

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