When you're shopping for tires, it's important to know what your vehicle can use. If you know how to read the sidewall, your current tires can tell you all the information you need to know in order to find new tires.
Learn how to read a tire sidewall now, and start shopping like a pro.
The good news is that learning how to speak basic tire won't take you too long to pick up. Your tires can tell you the following information (even if you can't read it yet):
We'll go step-by-step through the markings below.
Unlike clothing, there is no one-size-fits-all when it comes to tires. As such, one of the first things you'll want to know is what size tire you need for your vehicle. Tires use millimetres for size.
The easiest way to learn is with an example: P 225/55R18 97T
In our example, the first number (225) is the tire width (measured from sidewall to sidewall), and the next number (55) is the aspect ratio. The aspect ratio shows the relationship between the sidewall width and height (from wheel to tread). In this example, the sidewall height is 55% of the width.
The third number (18) is the wheel diameter in inches.
P 225/55R18 97T
Your tire might have a letter before the height. This letter tells you the type of vehicle the tire was designed for. Common letters and their meanings are:
The final number on the tire (97) indicates how much weight it can hold. The number corresponds to a load capacity found on a load index chart. In this example, 97 actually means the tire can hold 1,609 pounds.
P225/55R18 97T
The letter at the end of your tire indicates the maximum safe speed you can drive with the tire. Each letter corresponds to a certain speed rating. Letters go from "A" (lowest) to "Y" (highest). The only exception is "H" which actually falls between "U" and "V" instead.
A tire with a higher speed rating will corner and stop better, but they tend to cost more and wear faster as a trade off. Below are some of the more common speed ratings on tires:
Did you know that speeds were originally calculated in kilometers per hour? This is why we have ratings like "118 miles" and "112 miles." If you switch to kilometers, most ratings end in a "0." For example, "118 mph" for us is "190 kph" and "149 mph" is "240 kph."
On your tire, there will also be some small writing indicating the maximum inflation level. It will say something along the lines of "Maximum load XXX lbs at XXX psi." Most passenger car tires take between 41psi to 51psi. It's important to remember that this number represents the maximum inflation level. Heavier vehicles and loads can benefit from higher inflation levels while lighter vehicles and loads can do well with lower inflation levels.
A tire that has a "M+S" marking on it simply indicates that the tire has met minimum requirements and is authorized for use in snow. When there are accidents during winter months, Highway Patrol officers tend to look and see whether the vehicles involved have M+S tires installed or not.
Be mindful that having a M+S tire doesn't actually mean your tire will perform that well in the snow. It just means it has met the minimum requirements for snow.
Snowflake & 4 Season Symbols
On some tires, the manufacturer will use a snowflake or 4 season symbol in place of the "M+S" marking. A tire with a snowflake represents a seasonal snow tire that should excel in the snow.
Did you know that some tires are directional? This means they have to be rotated a certain way. You can identify a directional tire by the tread as well as an arrow showing the correct rotation direction. If a directional tire is mounted incorrectly, it won't work as intended.
Tires can also be asymmetrical, having an inside and outside to their tread. Many performance tires are asymmetrical. If you have a asymmetrical tire, it should be indicated somewhere on the sidewall. Your tires might be marked "inside," "outside," or "this side out," for example.
The Department of Transportation requires tires to be trackable. For this reason, tires have a DOT marking. This marking indicates the following:
You can already find the tire size and type of tire elsewhere. If you're curious about the manufacturing plant, look at the first two digits of the DOT number. If you have a code book handy, this tells you the location of the plant that made your tire. If you'd like to know when your tire was made, look for the date code. This tends to appear on only one side of the tire. There will be a string of 6-8 letters and numbers. The last 3-4 digits indicate the date. Prior to the year 2000, tires used 3 digits. After 2000, tires used 4 digits for the date. The first two digits tell you the week the tire was made, and the second two digits (or one digit) tells you the year.
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