Tire buying guides
How much can you tell about a tire just by looking at the sidewall? While pros might get everything they need to know from those cryptic numbers, all you see are a bunch of random characters. Aside from the name, you might as well be reading hieroglyphics.
No—you won't need to call in a scholar. You've already got a team of them right here.
Today, we're going to tell you everything there is to know about those numbers on the sidewall of your tire. After this, you'll be able to shop through tires like a pro, with the confidence of knowing exactly what will work for your car.
Why are the numbers there?
Before we talk about exactly what each number means, let's first discuss why they are there.
Here's the good news. There's very little chance that the numbers on your sidewall are unique to the tire or even the manufacturer. All of those numbers are subject to industry standards, meaning you can find them on most tires from most manufacturers. That's a good thing because everything you learn today will apply to any tire on the market.
Those numbers are descriptors. They tell us things we need to know, such as the tire's size, the load rating, what speeds it can handle, and even the max pressure the tire can contain.
The combination of the numbers and letters present tells us what the tire is good for, and you can find a solid replacement for that tire by matching the descriptors found on your old set.
Industry standards and standardized info
The reason those numbers are there is pretty simple, right? Yes and no. While we know what the numbers are trying to tell us, we still need to learn how to decode them to understand what they mean about your tires.
Let's start with the biggest number stamped on the side of your tire, the size. A typical size reading will read something like P225/65R17. Let's break it down so you know exactly how to determine size with those characters:
P: The confusing way of looking at this is understanding that the "P" means P-Metric. What does that mean? It's a passenger car tire. LT is another descriptor that may appear here, and all that means is you're looking at a ¾ ton or 1 ton light truck tire.
225: 225 is the tread width. It simply tells us how wide your contact patch or tread width is in millimeters. Hold onto this number because the next is heavily reliant on it.
65: Here's where things get a little confusing. The 65 in our size is the aspect ratio. This number tells us how tall the tire sidewall is. The 65 means the sidewall's height is equal to 65% of the tire's width. If the width is 225 mm, the sidewall measures 146.25 mm tall. Keep in mind that this does not tell us the overall height of the tire.
R: Back to the simple stuff. The R tells us that the tire is a radial, which you will find on most tires these days. However, a D may be present here, which simply tells us we're working with a bias-ply tire.
17: It's all making sense now, right? Well, now you're going to slap yourself on the head. The last number tells us the diameter of the wheel. In this case, the wheel is 17 inches. There's no real reason for the tires to use metric and imperial measurements other than the fact that we use inches to measure our wheels here in the States.
Now, you might run across a tire size that reads something like 33x10.5x17. That is the US version of tire measurements, and it's commonly found on off-road/all-terrain tires. It's simple, really. 33 is our total height in inches, 10.5 is the total width in inches, and 17 is the size of the wheel in inches.
The next largest number on our tire's sidewall is the load index. This essentially tells us how much weight the tire can support. In the example photo, that number is 102H. Drop the "H". We'll come back to it in a minute.
The load index is another standardized two, or three-digit number. Below you will find a chart that tells us the weights those numbers correspond to:
(Spoiler alert, 102 is good for 1,874 pounds per tire)
Below the load rating, you might find the load range in a much smaller font. This is an alphabetical character, and it essentially tells us more about the tire's construction and limitations. Below you will find a chart that tells us what the load range is, depending on the character displayed:
*Note: Though there is an H on this table, it does not correspond with the H that follows the tire's load rating. These are two different descriptors. *
So, what does that big H behind our load rating mean? That's your speed rating. It essentially tells us what speed the tire can safely travel at, and it's important to treat that as a maximum speed.
Tire speed ratings are also standardized, so whatever letter appears on your tire will correspond with the speed ratings listed in the below chart. Yes, most of the list is in alphabetical order aside from S, H, and V. That's because those speed ratings were introduced in the 1960s before listing the remainder of the speed ratings would be done in alphabetical order.
Alright, we've got the big ones out of the way. Now, what about the longest? That 12-digit number you see is actually the DOT code. In our example photo, that code is “DOT: SIMP LE01 2320” Think of this like the VIN. It can be used to tell us the date the tire was manufactured on.
For example, a tire with 2320 at the end of the code would have been manufactured on the 23rd week of 2020. This is an important number to pay attention to because it tells us how old the tire is and if it's safe for use.
The following three numbers we’ll discuss fall under the category of Uniform Treadwear Quality Grading. They appear at the top portion of the tire sidewall and tell us the rating of the tire’s performance according to a series of standardized tests that help us, as consumers, to determine how well a tire actually performs.
This one is super simple. The three-digit number following the treadwear rating tells us how long the tire will last. For example, our sample tire has a treadwear rating of 640, which would last around 6.4 times longer than a tire with a treadwear rating of 100.
While manufacturers are held to a standard, the rules are pretty loose, making it easier for them to put bigger numbers here. In other words, the rating can tend to be a little subjective and may not be completely accurate.
The next two-digit code you'll find is the traction rating. This number is found by dragging the tires across the asphalt in several tests and measuring the g-force rating produced. From best to worst, those ratings are AA, A, B, and C.
Next up is your temperature grade. Why is this important? Heat is your tire's worst enemy. This rating essentially tells us how much heat the tire can safely handle before it begins to break down and performance and safety are compromised.
We're almost done! The last number we're going to talk about is that M+S and the little snowflake you saw on our sample tire. What does that mean?
M+S simply means the tire can handle light mud and snow. In our example, mud and snow are spelled out, but the symbol may appear as an alternative and is typical to find on an all-season tire to let us know it can handle those conditions.
The snowflake is present to let us know that we're working with an all-weather or winter tire that can handle moderate to severe winter conditions. It's found on the Three Peak Mountain, and is a standardized rating to ensure the tires can be used safely in wintry conditions.
We get it! It's not that simple. Well, it is, but memorizing everything we covered can be challenging. That's alright. You now have the means to develop a pro-level understanding, but there are still pros to guide you along.
If you have any more questions on what these numbers mean or what tires will replace the ones you're currently running, give us a call. Our pros are more than happy to fill you in on any details and help you track down the perfect match for your car!
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