How to Read Tires

Tirespeak: Know How to Read Your Tires

When shopping for tires, it's important to know the meaning of all those mysterious embossed letters on the sidewall of the tires. It's not as complicated as you may think. Here's how to decipher them.

• The first letter in the series is the tire's class designation -- for example, "P" for passenger, "LT" for light truck or "T" for temporary.
• That letter is followed by the tread width. In this case, "235" means this tire's tread is 235 millimeters in width. So larger tread-width numbers mean wider tires

• The next number in the series is called the aspect ratio -- in this case it's "75." That's calculated in a ratio compares the height of the sidewall and width of the tire. So in this case, "75" means that this tire's height is 75-percent of the total 235-mm width.
• The aspect ratio is followed by a letter that tells what type of construction this tire has. In this case, "R" stands for radial. (Most modern tires are radials. In radial tires, the internal tread-wires run perpendicular to the direction of the treads.)
• The letter indicating construction is followed by a number (figure C) designating the diameter of the wheel. In this case, this particular tire is made to fit a15-inch wheel.

• The last number in the series is the load index which tells the amount of weight the tire can hold. Higher load-index numbers indicate greater load-carrying capacities. In this case, "105" indicates that this tire can hold up to about 2000 pounds.
• The last letter in the series is the speed rating. Tires like this with an "S" rating (figure E) can handle speeds up to 112 mph. Letters later in the alphabet correspond to higher speeds. A "Z" rated tire, such as some high-performance tires, can handle speeds up to around 190 mph.
  

• The treadwear rating number indicates how long the tread will last under typical driving conditions. The higher the number, the longer the tread will last. On this high-performance tire, the "220" indicates that this tread has a relatively short live, compared to some other tires. (Because of the materials and configurations, high-performance tires typically wear faster than more standard tires.)
• The traction rating is an indicator of the level of traction the tire possesses. Traction ratings can range from A to D. In this case, this high-performance tire gets a "AA," indicating a high level of traction.
• The temperature rating is also an A to D letter rating, with A being the highest rating. In this case, the "A" means that this tire can withstand temperatures even in very hot climates such as Arizona.

Tire Expiration Date

How do I determine how old my tires are? Can anyone tell when a tire was manufactured? Is there a tire date somewhere on the tire?

These are all good questions. All tire manufacturers are required to mark each tire with the date of manufacture. So evey tire has the date stamped right on the sidefor all to see. For all tires from the year 2000 to present, the date of manufacture are the last four digits of the DOT code. The first two digits are the day of the week and the last two digits are the year. Now you know exactly how to find out just how old your tires are. Use the location chart below to help locate the tire date.