Without a doubt, modern tires feature a perplexing array of numbers and symbols embossed on their sidewalls. While sizing figures are perhaps the most frequently scrutinized digits on a tire, there are additional crucial details to uncover if you understand how to interpret the information.

Let’s start with sizing, since getting correctly sized tires is as much a matter of safety as it is performance. On this continent, customers are generally faced with information which looks like the following: 275/65R20. That may seem a trifle confusing but relax – it’s much worse than it seems. Before we break down what each set of digits denote, you gotta know there are three different measuring standards across those three different groups of numbers.

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Let’s begin with the basics. The last two digits – 20 in this instance – indicate the wheel diameter measured in inches. The tire we’re discussing is designed to fit a wheel that is twenty inches in size. In this context, the letter ‘R’ signifies radial construction, although some brands and individuals argue that it represents radius or rim.

The initial trio of digits, which is 275 in this instance, indicates the width of a tire measured in millimeters. Indeed, my dear reader, the metric system is prominently displayed on nearly every tire you encounter in our country. Unfortunately. This figure represents the width of the tire from one shoulder to the other across its tread pattern, so a larger number signifies a wider tire. For instance, a tire rated at 225 is narrower compared to one rated at 235. Interestingly, most of these measurements typically conclude with the digit five. What a curious coincidence!

Next, we find two digits, shown as 65 in our example. This is called the aspect ratio and refers to the measurement of the tire’s sidewall from the edge of the metal wheel to the top of the tire tread. It is a percentage of the tread width. The digits in our example tire size mean the sidewall height is 65 percent of the tire’s 275-millimetre tread width.

Why does this matter? Let's take our example tire and compare it to one that measures 285/65R20. Although both tires have a sixty-five percent aspect ratio, the second tire will be taller overall because 65 percent of 285 is a bit more than 65 percent of 275. This height difference could potentially lead to clearance problems with your vehicle's suspension or bodywork. Moreover, it can affect your speedometer readings, as a taller tire requires more time to complete a full rotation. For instance, when your speedometer shows 60 mph, you might actually be traveling at only 59 mph.

Another crucial set of four digits to be aware of is the ‘date code’ found on tires. This code consists of four digits and is typically located in a small oval imprint on the tire's sidewall, occasionally appearing on the side opposite the sizing information. The initial two digits indicate the week of the year, while the final two represent the year of manufacture. This information assists consumers in determining the production date of a tire.

For instance, a date code of 1424 indicates that a tire was manufactured in the 14th week of 2024. This information can be particularly helpful when purchasing a used vehicle from a seller who claims it has brand-new tires. If a quick inspection of the tires reveals a date code of 0319, which signifies that the tires were made in the third week of 2019, it becomes clear that the seller may not be completely honest (or might be unaware of the actual age of the tires). You can use this insight to negotiate a better price or at least inform the seller about the actual condition of the tires. Reputable brands like Sailun consistently include a date code on their tires.

Speed ratings were once highly significant in the ‘80s and ‘90s, but the widespread availability of performance has mostly pushed those ratings into the past. Nowadays, with even a four-door Camry capable of reaching 60 mph in under six seconds, it’s essential for nearly all tires to be designed to handle a respectable level of power.

It's important to understand that the speed rating scale is not linear. The rating 'H' lies between 'U' and 'V', with the general belief that 'H' represented high performance in the past. Tires rated 'H' are suitable for speeds up to 130 mph, while 'V' tires can manage up to 149 mph, and 'Z' is designated for speeds exceeding 149 mph. In later years, 'W' and 'Y' ratings were introduced to accommodate the increased velocities of high-performance sports cars. Generally, tires with high speed ratings provide excellent grip and braking capabilities, but they may also wear out faster and have a reduced tread lifespan.