Tires separate your car from the road. They form vital parts for the braking, steering, and power systems of your car. Tires work relentlessly to ensure that your car delivers a safe ride. Due to the vital role tires fill in your daily life, Bob Howard Acura recommends that you should understand tire basics. Learning tire fundamentals requires that you learn about tire codes. 

Finding tire codes

Tire-makers inscribe every tire they make with a standard identification code. This code usually has ten or more characters and tells you all you need to know about your tires. You can find tire codes on the sidewalls of the tires on your car. It looks something like this: P230/52R16 91S. The U.S. Department of Transportation uses these codes to standardize the process of making and selling tires.

Decoding tire codes

Intended use. Tire codes can start with an optional letter that indicates the type of vehicle for which the tire was manufactured. Some of the most common codes follow:

  • P = Passenger car
  • LT = Light Truck
  • T = Temporary

Tire width. The next section of the tire code describes the width of the tire in millimeters using a 3-digit number. Auto-parts makers design wheels to accept a standard tire width. However, you can usually put tires with slightly different widths on your rims. Wider tires usually give your car more traction, but narrower tires will usually improve gas mileage. Ask your dealer first if you want to put a different size tire on your car.

Slash. Tire makers put a forward slash (/) after the tire width to separate the width from the aspect ratio.

Aspect Ratio. After the width, a 2-or 3-digit number describes the ratio of the height of a tire to its width. If a tire does not have these numbers, the tire has an 82-percent ratio.

Construction. A letter following the aspect ratio in the tire code indicates the way the tire was made. Some of the possibilities include the following:

  • B=Belted.
  • D = Diagonal
  • R = Radial
  • Cross-ply tires have no value here.
  • Some speed-rated tires have a “Z” designation that precedes the construction indicator.

Rim diameter codes comprise two-digit numbers This describes the wheels on which it can fit. Most cars use so-called “inch rims” and list the diameter of the rim using inches.

Service description. All speed-rated tires manufactured after 1991 that do not come with a “Z” rating have a service description. The first part of the service description is a two-digit number called the load index. This shows how much weight a tire can support. Most consumer-oriented tires come with load index values between 70 and 110. You should ask your dealer to recommend a special load index if you use your car to carry or pull unusual loads.

A letter following the load index indicates the speed rating of a tire. For example, “S” is a rating for a family-size car tire that can run up to 112 miles per hour. Other speed ratings include:

  • L = 75 mph
  • N = 87 mph
  • Q = 100 mph
  • R = 106 mph
  • H = 130 mph
  • V = 149 mph

See what you've learned

Now that you have learned tire basics, you can decode the sample tire code listed earlier, P225/50R16 91S. Such a tire is a radial passenger-car tire that was 225 millimeters wide. The sidewall is half as tall as the width of the tread. This tire installs on a 16-inch-diameter rim. Cars using this tire should not go faster than 112 mph or carry a load heavier than 1,356 pounds.