Explaining Tire Sidewall Markings

Everything rides on your tires (yes, pun intended there), yet for such an indispensable part of your vehicle, many drivers seem to have a pretty poor understanding of them. One of the least-understood aspects of tires is the set of coded markings on the sidewall; for many drivers, they’re as indecipherable as etchings on a cave wall. This information might seem arcane, but it does include a lot of important information about the tire’s design, performance and capability. We’re going to break it all down and hopefully pass on some information about your tires that might actually come in handy for you someday.

Why are those numbers there at all?

Regardless of the tire, the manufacturer or the country of origin, the sidewall markings on tires are all standardized and compliant with tire industry regulations - all the info contained here will apply to any tire on the market. The numbers are descriptors for tire size, load rating, the max speed a tire can handle, and max inflation pressure. The best tire sizes and specs for any given vehicle are determined by the engineers and design team at the vehicle’s manufacturer; in other words, those are the original equipment it left the factory with. Understanding your tire’s sidewall markings will give you the information you need for the purchase of your next set of tires.

Here’s a typical set of markings for a tire:

225/65R17 102H UTQG: 600AA DOT Code: SIMP


Let’s start off with decoding the tire size information:

Tire Size

Here’s a typical tire size designation: 225/65R17, such as the Atturo AZ610..


● 225: this tells you the tread width, aka the “contact patch” or “footprint” width, in millimeters. A 225 width is fairly commonplace for passenger tires, and this will tie in with the next part of the designation.
● 65: this refers to the tire’s aspect ratio, or how tall the sidewall is. In this case, it means that the sidewall height is 65 percent of the tread width; 65 percent of 225 is 146.25 mm. This does not, however, tell you the overall height of the tire.
● R: this denotes a radial-construction tire, which has been the industry standard for decades. Bias-ply designs are sometimes still found for special-trailer sizes, commercial or industrial tires; those tires would have a “D” in this part of the size description.
● 17: this tire is designed for a 17” rim. Yes, most of the rest of the world has gone over to metric measurement, but tires still are classified by inches of rim size.

Other tire designations (prefixes) that don’t apply to this tire include:

● P: formally denotes “P-Metric,” but for all intents and purposes, it means “passenger car tire.”
● LT: this is a pretty simple one, as “LT” just stands for “light truck.” Light truck tires are engineered for the weight, power, torque and load capacity of trucks, and feature reinforced construction and usually a more heavy-duty tread formulation.
● C: the “C” prefix indicates a commercial tire; designed for light, medium or heavy trucks, commercial tires have specific requirements for load capacity and durability, and are subjected to rigorous testing to ensure their performance.
● ST: this indicates a tire that’s designed specifically for trailer service. Trailer tires might look like passenger or light truck tires, but trailer tires are subject to a different set of forces and stresses from vehicle tires and should never be used on the vehicle itself.

This tire size designation doesn’t apply for all tires across the board, though. You might sometimes run across an all-terrain or mud-terrain tire for light trucks with a size marking that reads 33x10.5x17, for instance. In this case, it would mean that 33” is the tire’s overall height, 10.5” is the width of the contact patch, and it’s designed for a 17” rim.

Load Index

The next number in this sequence is a code for the vehicle’s load index, i.e. the amount of weight that each tire can safely support. Most car tires are in the 80-90 range, while light truck and SUV tires can be anywhere along the 90s to 120s.

The 102H (never mind the H, we’ll come back to that shortly) code means that each tire is capable of; in this case, 102 means 1874 pounds per tire, or a gross vehicle weight of 7,496 pounds. That’s a lot of weight, and the load index number is especially valuable for drivers of light trucks that might haul heavy loads or do heavy towing duty.

The table below shows more information on understanding load index, and what each load index number corresponds to as far as actual weight capacity:



Below the load rating numbers, you might see another alphanumeric in a much smaller font size. This would be the load range, a number that shouldn’t be confused with load rating. Load rating pertains more to the tire’s design and construction, and its limitations. This chart explains load range as represented by the characters displayed:


Yes, there’s an H at the bottom of this table, but that’s still not tied in with the H next to the load rating number. Let’s get to that now:


Speed Rating

Now we get to that H marking; the H in “102H” is the tire’s speed rating, an indication of the highest speed a tire can safely handle. This should be regarded as a maximum speed for your vehicle.

Tire speed ratings are also standardized and were devised decades ago. In the table below, you’ll notice that the speed ratings are alphabetical, with the exception of H, V and Y. Those particular ratings were introduced in the 1960s, before the rest of the system was put together in alphabetical order:

DOT Code

The DOT Code is designed to let you know when a tire was manufactured; this might be a 12-digit number, but in this case it’s “DOT: SIMP LE01 2320”. Like a VIN number, this code can tell you the date of manufacture; the 2320 means it was manufactured on the 23rd week of 2020. This is important information to know, as tires have a shelf life and even a tire that’s brand new and has never been on the ground shouldn’t be considered safe to use if it’s seven years old or older.


UTQG

UTQG stands for Uniform Treadwear Quality Grading; this number toward the top of the tire’s sidewall describes the tire’s performance and is determined by a series of standardized tests.

Treadwear Grade

Treadwear grade is expressed as a three-digit number, designed to tell us how long a tire can be expected to last. In this instance, the number is 600, which can be interpreted as a tire that would last 6.4 times as long as a tire with a treadwear grade of 100. This is a standardized number, but it also comes with a “fudge factor” that can be somewhat subjective and may not be 100 percent accurate.


Traction Grade

Next up in the UTQG designation is the traction rating, which is in this case the “AA” notation. The industry determines the traction grade by dragging the tire across asphalt in several test scenarios and then measuring the G-forces produced. Traction grade is rated from AA to C, in a best-to-worst sequence:



Temperature Grade

Excessive heat buildup is the enemy of any tire; it weakens the tire’s internal structure and causes premature wear and possibly failure. The temperature grade rating indicates how much heat a tire can safely handle, as a function of speed.





M+S and 3PMSF

The M+S and 3PMSF ratings are special performance grades for specific types of tires. The M+S rating means that the tire is capable of managing light snow and mud; sometimes this is expressed as “Mud and Snow” rather than M+S. Regardless, this is a fairly common feature on all-season tires.

3PMSF stands for “Three Peak Mountain Snowflake,” referring to the little infographic. A tire with the 3PMSF rating is suitable for moderate to severe winter conditions; without going into too much detail, let’s just note that the tire industry sets the bar much higher for 3PMSF than for the M+S certification. This is a rating you’re likely to see for all-terrain light truck tires, dedicated winter tires or all-weather tires.



This is a pretty good summation of what the information on your tire’s sidewall means and how it can be interpreted. You don’t have to have a pro-level understanding and you don’t have to memorize all of it, but as a driver you can at least be informed about what your tire info means; it’s all a description of the tire’s performance limits and construction.