CAN TIRES TALK?

Modern tires have a story to tell. The information that they convey is important and helpful, but also potentially confusing. Here is a recap and explanation of the types of information included on all new tires. Do you know what they are trying to tell you?

TIRE SIZE:

To give a real-world example, let’s look at the O.E tire for a 2021 Honda CR-V in EX trim. First, the size of the tire is 235/60R18, one of the most popular sizes, and it is used on a variety of vehicles. The “235” means that the tread is 235mm wide. Next, the “60” tells us that the height of the sidewall of the tire is 60% of the tread width. In this case 235mm x .60 = 141mm, the sidewall distance from wheel rim to the outside of the tire. In general, less sidewall height gives sharper handling but a rougher ride. Then, the “R” designates that the tire is of radial construction. Radial describes the way the cords of the tire (the part under the tread) are positioned sideways, which makes for better ride, steering, and handling as compared to the old bias-ply design. Nearly all tires sold as original equipment or aftermarket are radial. Finally, the “18” tells the diameter of the wheel in inches.

TIRE LOAD AND SPEED RATING:

Somewhere on the tire (to the right of the tire size) will be the designation for tire load and speed rating. In the case of our sample Honda CR-V it is 103H.

The “H” is one of the letter grades used by the tire industry for passenger car, truck, trailer, and utility tires to indicate the top speed that the tire can be safely driven. Here is a chart that shows the speed limit by letter identification:

SOURCE: US DOT 

TIRE LOAD AND SPEED RATING (continued):

The “103” is a rating on a scale from 65-150 to indicate the weight that a tire can safely carry. The rating of 103, for example, can carry up to 1,929 pounds per tire. Most passenger car tires will be rated in the 95-110 range, but others, like trailer tires or heavy-duty truck tires will be well outside of that range

LOAD INDEX CHART

SOURCE: US DOT

So, the combination of a number and a letter tells you what you need to know about the tire’s ability to handle both weight and speed safely.

D.O.T. CODE:

Tires that meet the safety requirements of the D.O.T. are marked with the letters “DOT” followed by a series of numbers. Only tires marked with valid D.O.T. codes can be sold in the United States. In this code, the “DOT” is a constant, but the numbers in the code consists of a 2-digit manufacturer-specific factory code, a 2-digit tire size code, an optional 4-digit manufacturer-specific use code, and a 4-digit date code. The first two numbers of the date code are the week of the year the tire was made; the second two numbers are the year of manufacture. For example, the tires on our sample Honda could have a date code of “4820”, meaning that the tires were made during the 48 th week of 2020. The date code is very important for recall purposes and to provide a reference for when the tires should be replaced, regardless of wear.

UNIFORM TIRE QUALITY GRADE (UTQG):

Tires also include a three-digit number followed by two letters as part of the Uniform Tire Quality Grade (UTQG) rating system used by all tire manufacturers. The UTQG rates treadwear, traction, and temperature. The Honda’s tires in our example have a UTQG rating of 700-A-A. The “700” is a wear indicator that gives you some idea of how long these tires should last from new. The rating is based on a scale of 100 to 800, so in our example, the 700 designation means that the tire should wear well compared to the baseline tire from that same manufacturer.

Then, the first “A” is the wet friction traction grade and it is somewhat like a report card, with grades from best to worse being AA, A, B, and C. The second “A”, for temperature, means that these tires meet the highest standard for heat resistance measured as simply (best to worst) A, B, or C.It is important to note that you cannot reliably use these measurements to compare tires from different manufacturers. Each tire company grades their own tires according to a standard test format provided to them by the D.O.T.

MAX INFLATION PRESSURE:

The numbers shown on the tire is the maximum pressure allowed, not the correct pressure for the specific vehicle. The pressure information for the vehicle will be on the tire load sticker and in the owner’s manual.

OTHER:

Finally, there are other pieces of information on some tires that give specific information. For example, some tires are designated as “run flat” or “MOE”, meaning that they can run for up to 50 miles without any air pressure. These types of tires have very rigid sidewall construction that allows them to hold up the weight of the vehicle even if all air is lost. You may also see the letters “M+S” on the sidewall of tires used on vehicles like the Honda. These letters stand for mud and snow. M+S does designate that the tire is designed for use in all seasons, including rain/mud conditions and light snow.

So, yes, tires do have a story to tell, but it does take some skill to fully understand the messages they are sending.