Become a Car Tire Expert

August 14th, 2020 by

Two discount tires are shown against a black background.

The numbers on your tires provide you with a tremendous amount of information about your tires, much more than you might realize at first. At a glance, if you know how to read your tire numbers, you can see the type of tire it is, how wide the tire is and its aspect ratio, as well as its design. The tire numbers also tell you the wheel diameter they are designed for, how much load they are meant to support, and their speed rating. All of this information can help you make sure you get the right tires for your vehicle when you shop for discount tires in Cincinnati.

You might not feel like you need to be able to read your tire numbers and, to be completely fair, it’s not 100% essential to get through everyday life. That being said, it’s definitely something that can help you out in a pinch if you need new tires for your car and want to make sure you get the right ones. If you go to a tire shop for the first time, it’s a good idea to double-check the tires they put on your vehicle to make sure they are the proper ones you need. Even if you trust your mechanic, it’s still a good idea to make sure a mistake didn’t happen when replacing your tires.

Today, we’re going to take a few minutes to go over the information on your tires so you’ll know how to read them. We’ll also take a look at other stuff you need to know, like how to check and care for your tires and when to replace them. By the end of this, you’ll be a tire expert, ready to take on the world and drive with confidence in your tires.

A Brief History of Tires

If you go back far enough, tires were originally made of a piece of wood (ignoring stone wheels because we’re talking about tires here). From there, someone had the bright idea to replace the wood with leather to allow for a more pleasant ride, and eventually, that was replaced by rubber for an even better experience. The original rubber tires were made with solid rubber, rather than the air-filled ones we have today.

In the late 19th Century, air-filled rubber tires were invented and utilized, with tread tires introduced following that in 1905. Synthetic rubber was developed in the early 20th Century, which made tire manufacturing much more commercially viable. In the 1950s, the Michelin tire company developed and patented the radial-ply tire, and by the 1960s, that design taken over the auto tire industry. Modern tires still typically have this radial design, and there are now a wide range of types, based on what they are designed to handle.

Introduction to Tire Codes

Now that we have a sense of where tires have come from, let’s get back to that tire code we first talked about and get a lot more in-depth with it. First things first, by “tire code,” we’re talking about all those numbers and letters you’ll see on the outside of your tires. Some of this information is very straightforward or really not all that useful for you as a typical driver. For example, you’ll usually see the manufacturer’s name along with the name of the tire (we’ll talk a bit more about brands and types of tires later). You’ll also find the US Department of Transportation (DOT) tire identification number on the tire (we’ll also look at that much later).

The meat and potatoes, so to speak, of information on the tire comes down to a series of letters and numbers that tell you very specific and useful information about your tire. First, let’s take a look at what this will look like on your tire, and then we’ll break it down. So, here’s what you’ll probably see (if not exactly this, something with a similar pattern of letters and numbers):

“P215/65R15 95H”

Got that? Good. So, what does all that mean? Well, let’s go piece by piece.

The side of a tire, including the tire code, is shown.

Reading a Tire Code – Type, Width, Height

It starts with a letter that lets you know the type of tire you’re looking at. In the above example, and what you’ll probably find on your vehicle, is “P,” which means it’s a tire designed for use on passenger vehicles like your car or a small truck or SUV. If that was “LT” instead, it would mean the tire was designed for use on a light truck, which you’ll often find on a large SUV or pickup. A “T” indicates a temporary spare tire, which should only be used for a short time, while “ST” is for a utility or boat trail and “C” indicates a tire for a commercial vehicle.

Next up, we have three numbers, in this case, “215.” This is a measurement, in millimeters, of the width of the tire itself, from sidewall to sidewall. So, our example tire is 215mm in width. After that is a slash, then a two-digit number that indicates the aspect ratio of the height of the tire’s sidewall, not the total tire, compared to its width. In the above example, it says “65,” which is pretty typical.

Now we’re about to do some math, and we apologize in advance, but it’s worthwhile if you really want to understand what your tire code means. So in the example we chose, we see the width and aspect ratio is “215/65.” This means the tire is 215mm wide, and the height of the tire’s sidewall––from the wheel rim to the outside of the tire’s tread––is 65% of that width. A quick calculator use tells us the height of the tire is, therefore, about 140mm.

Reading a Tire Code – Design and Wheel Size

Still with us? Good. Next up, we have a letter that tells us how the tire was constructed. In this case, the “R” means that it is a radial or radial-ply tire. The vast majority of tires use a radial design, so this is almost always what you’ll see. A “D” means it has a bias ply design, while a “B” indicates a belted design, which is very rare these days.

The number after the letter tells you the size, in inches, of the wheel diameter it’s designed to fit (your tire code has the width indicated in millimeters and the diameter in inches). In our example, the tire code says “R15,” which we know means it’s a radial tire, and it is designed for a 15-inch wheel. You’ll typically see diameter measurements of anywhere between 8 and 28, depending on the type of vehicle you’re looking at, all of which are fairly common.

Reading a Tire Code – Load Index and Speed Rating

Finally, we come to the load index and speed rating on the tire. This is represented by a final two-digit number followed by a letter. The number is the load index for your tire, and the letter tells you its speed rating. Here’s the simple idea: your vehicle has a set load index and speed rating that it’s designed for, and the tires should match or be better than it.
You can find this information on the service description sticker on your vehicle. This sticker is usually placed on the driver’s side door jamb, though it may sometimes be inside the gas cap cover. You’ll also find this information in the owner’s manual for your vehicle. It will be indicated as a two-digit number and a letter, just like what you see on a tire. All you really need to know is this: match what your vehicle says to your tires, and you’ll be fine.

So, if your vehicle’s service sticker says “95H,” then make sure your tires also say 95H. The 95 indicates that each tire can handle a certain amount of load or weight––the higher the number, the more it can handle. Each tire with a load index of 90, for example, can handle up to 1,323 lbs of weight, while each tire with an index of 95 can handle up to 1,521 lbs. You can safely choose tires with a load index higher than what your car says it should have but never go lower.

The letter tells you the speed rating, or how fast you can safely drive on the tires. This is not an excuse to drive faster than the posted legal speed limit; however, only an indicator of what your tires should be able to handle. A speed rating of “H” means the tires can go up to 130 mph, while a “Z” rating means they can go more than 149 mph and not come apart. Always choose a tire with a speed rating at least equal to what your vehicle’s service sticker says or higher, never lower. Also remember that this just means the tires can handle this speed, not necessarily your vehicle––always drive safely and follow posted speed limits.

A gloved hand is changing the tire at a discount tire shop in Cincinnati.

Types of Tires

That was a lot of information, wasn’t it? We know, but now you know what all of those letters and numbers you find on your tires actually mean. Even if you don’t remember all of that, which is pretty understandable, there are a few things that you should have tucked away in your back pocket to help you when buying tires.

For starters, you need to remember that there are different types of tires––both in how they are made, the kinds of vehicles they are designed for, and the road conditions they are designed for. You will likely never need anything other than radial tires, so as long as your tire says “R” where it should, then you’re good. But you might have a use for some other types.

If you have a car, then you’ll probably have passenger tires, which might also work for a small SUV and even a light-duty pickup. A larger SUV or full-size pickup, however, will probably have light truck tires on it. This is very important since these tires are designed to handle the larger size, greater weight, and increased demands that you will typically place on such a vehicle. If you need LT tires for your vehicle, then always make sure that is what you get when you buy new tires.

Similarly, you might want to consider different types of tires in terms of the conditions they are designed for. Here are a few of the more common tire types you’ll find and what they are designed to handle:

  • All-Season Tires: These are your basic tires designed for, as the name suggests, all seasons. They work well on dry roads and on wet, summer and winter, and are a great choice for an everyday tire on your vehicle.
  • All-Terrain Tires: These tires are designed with a large and highly effective tread pattern that helps them keep traction in all kinds of terrain, both on and off-road. These are a great choice if you like to go off-roading, or if you often have to drive on dirt and gravel.
  • Mud Tires: Just like the name suggests, these tires are specifically designed to help you maintain control in mud. They work well in mud and sand, where other tires can let you down, but are not particularly comfortable on paved roads.
  • Snow Tires: These are tires designed to work in snowy conditions, with tread that helps you maintain traction and move slush and snow out of the tires. They can help avoid skidding and slipping in snowy conditions and are a great choice for winter in areas with lots of snow.
  • Summer Tires: These are light performance tires that are designed to work well in both wet and dry conditions. They are specifically engineered for use in warm weather and are not good in cold conditions or in snow.
  • Performance Tires: As the name suggests, these tires are designed to offer the best performance possible, giving you excellent grip and traction, with high-speed ratings to handle high-performance vehicles. They can work well in light rain but are best for generally dry conditions where you need an excellent grip.

Different Tire Brands

There are quite a few different tire manufacturers out there, and you’ll probably find numerous brands when you go to get new tires. In general, we recommend sticking with big names and major brands such as Michelin, Goodyear, and Pirelli. As long as you go to a reputable dealer or tire center, you should be fine with the selection they offer, though a little research beforehand is never a bad idea. While the brand certainly matters, it’s typically more important that you choose the right size, type, and functionality for your vehicle.

Someone is putting air in a tire on a white car in Cincinnati, OH.

Caring for Your Tires

General maintenance and routine care for your tires starts with inspecting them on a fairly regular basis. You should make a habit of looking at your tires every time you get into your vehicle, even if it’s just a casual glance. As long as you know what your tires should look like in general, you’ll easily be able to tell if something is wrong. Once every couple of weeks, you should go a bit further and really give your tires a good check to make sure they are in proper working order.

When you do this, look at the tread on your tires––this is the part along the surface that comes into contact with the road, which has grooves and comes in different shapes. You want to check how the tread is wearing down. Ideally, it should wear down fairly evenly across the tire. If the inside or outside of the tread is significantly more worn than other parts, then this can mean your alignment is off, or you have an issue with your wheels, so get it checked out if you do.

You should also check your tread depth on a fairly regular basis; every few months is a good idea. Simply take a penny or quarter and insert it with the president’s head facing downward. You should not be able to see the top of the president’s head––this means your tread is still deep enough, and your tires are fine.

If you can see the top of the president’s head, then your tread is quite worn. If you use a penny, then you need to replace your tires as soon as possible. By using a quarter instead, you have more time to react––you should get your tires replaced in the next couple of months.

Also, be sure to check your tire pressure from time to time, especially if your tires seem to be a bit flat or out of shape when you look at them. You can buy a tire gauge and keep it in your glove compartment; they are inexpensive and easy to use. Many gas stations also have air pumps you can use, which typically include a pressure gauge to see how your tires are doing.

When to Replace Your Tires

Obviously, you want to replace your tires if you notice that the tread is significantly worn, or if you find the pressure is low on a frequent basis, as this means you probably have a leak. Even if your tires look great, you also need to make sure you replace them within ten years of when they are manufactured, because rubber simply breaks down over time. But how do you know when your tire was made?

Remember that DOT identification number we mentioned a while ago? Well, it will include some letters and numbers––the letters can indicate where it was made. But the numbers will end in four digits, something like “3318.” These four numbers tell you when the tire was made, the first two are the week and the second pair tells you the year. So if you see “3318,” then that means your tires were made in the 33rd week of 2018.

Do your tires say “xx10” or even earlier? Then it’s time to replace them.

When you notice it’s time for new tires, visit us at McCluskey Chevy in Cincinnati for all your tire needs, and we’ll make sure you drive away with confidence.