How to Read a Tire Sidewall
How to Read a Tire Sidewall
Let us help you decode the tire size, age, speed rating, and other important data that can be found on a tire.
By Austin Irwin
Rigatoni and tagliatelle are both types of pasta, but each serves a different purpose. The former pairs well with chunkier sauces that can fill in its tubes and ridges, while the latter complements thicker sauces; its broad and flat shape offering a sturdy plane for the likes of bolognese sauce to rest.
Tires are no different. They may seem—and in many crucial ways are—similar, but different types of rubber serve different purposes. Due to this, you'll want to make sure the rubber you put on your car best serves your driving needs. There's a lot of pertinent information to consider when looking into tires, too, but thankfully the majority of the details are listed right on the sidewall. Tires are a complex mix of raw materials, chemicals, and other trimmings that separate one tire from another.
But you don't have to be a tire engineer or car guru to know the fundamental details about these rubber doughnuts. We've created this guide to help you learn about everything there is to know about tires. We'll use a variety of different tires in this guide, such as passenger-car, light-truck, winter, and even some extreme-performance summer tires, as what's shown on the sidewall can vary.
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How to Find Tire Size
The best place to start is with the large numbers on the sidewall. These indicate fundamental tire dimensions. In this example, the 235 indicates the width of the tire at its widest point, measured in millimeters. Directly after the slash is the tire's profile or sidewall height, indicated as a percentage of its width (in this case, 55 percent).
The "R" that follows denotes typical radial construction. Bias-play and belted tires, on the other hand, feature a D or B in this position. In this example, the denotation is closed off with the number "19" as this tire fits a 19-inch wheel. The sidewall of the tire is really the most obvious place to find the wheel size of any vehicle, given this information is otherwise hidden on the inside of the wheel, a door-jamb placard, or the owner's manual.
Sometimes the tire size is immediately preceded by letters. A "P" indicates p-metric, or a tire used for passenger cars, while "LT" or Light Truck is primarily found on SUVs, minivans, or pickup trucks. Additionally, "HL" stands for a high-load rating. It's often found on electric vehicles. Other letters, such as the "ZR" on the Porsche 911 GT3 RS tire (shown in the lead image of this article) indicate a high-speed rating. More on that in a moment.
While tire sizes are nearly always listed in millimeters, there are a few occasions where the order of the dimensions listed is somewhat swapped and shown in inches instead. On larger or Light Truck tires, the first number of the tire size is shown as a 30, 33, 35, or in the case of this 8780-pound Ram 2500 HD AEV Prospector XL, a 40. That tire is roughly 40 inches in diameter or height. The number after the "X" shows width, in this example, 13.5 inches, followed by the "R" indicating radial construction before the wheel diameter and the letter "LT" for Light Truck. If the AEV's enormous Toyo Open Country M/T tires were instead listed in millimeters, as many new Light Truck designated rubber is, it would appear as 340/85R17.
How Much Speed Can a Tire Safely Handle?
The "95W" seen on these Bridgestone Potenza RE-71RS tires describes two very important performance ratings: how much weight each axle can carry and the speed rating the tire can safely operate. In this example, the "95" indicates a maximum load index of 690 kilograms (or about 1521 pounds), and the "W" designates a speed rating of 167 mph. The speed rating is important because although your vehicle's speedometer might max out at 170 mph, it's ultimately the tire's rating that will determine the highest speed a given vehicle can actually handle. The highest speed rating out there is "(Y)" which means the tire is rated for speeds "in excess of 186 mph." Here's a list of the most common speed ratings:
- L: 75 mph
- M: 81 mph
- N: 87 mph
- P: 93 mph
- Q: 99 mph
- R: 106 mph
- S: 112 mph
- T: 118 mph
- U: 124 mph
- H: 130 mph
- V: 149 mph
- W: 168 mph
- Y: 186 mph
- (Y): more than 186 mph
- Z: more than 149 mph
How to Read Tire Age
Like a birth certificate, your tires have documentation that pinpoints when and where they were made. To find this, look for the giant "DOT" (Department of Transportation) stamping. The sequence of letters that follows is a code that represents its manufacturing plant, which is then followed by the manufacturing date. The first two digits indicate the week the tire was built followed by the production year. In this example, the "1YL" represents the Nokian Tyres plant located in Nokia, Finland, and the "3323" means it was produced the 33rd week (mid-August) in 2023.
According to the experts at Tire Rack, tires five years or older should be inspected periodically for signs of degradation. Tires more than six years old, even if they haven't been mounted to a wheel and properly stored, should not be used. Any tire, even a spare, manufactured more than 10 years ago is simply too old to be trusted. Keep in mind, that a vehicle's model year or production date doesn't directly correlate to the tire's production date. We've seen new cars rolling on tires with date codes two years older than the vehicle they're mounted to.
Many factors contribute to the lifespan of a tire, such as treadwear, driving habits, rotation schedule, and the unfortunate pothole or stray roofing nail. While not necessarily a direct predictor, every tire has an indicated tread life value that's been earned by the Uniform Tire Quality Grade (UTQG) standardized test conducted by each manufacturer. However, tires with the same treadwear rating from different tire manufacturers could have dramatically different warranties, as tiremakers are allowed to under-report for marketing purposes. We suggest looking at a specific tire's tread-life warranty for a more accurate estimate of tire life expectancy.
Tread depth does a lot for braking distance on wet surfaces, and as such, it's important to keep your eyes on the tread wear indicators that live in the valley of those rubber grooves. The little bumps measure 1.6 mm high and, as a tire is used and its tread is eventually consumed, the indicator will eventually be at the same height as the rest of the patterns and grooves. It's at this point the tire may no longer be safely effective at providing enough traction to quickly stop a vehicle.
The "A" after "Traction" and "Temperature," shown in this example is also somewhat of a rubber report card. This value represents the tire's coefficient of friction while the brakes are locked across a wet surface.
Don't get this confused with a hydroplaning rating, it's not. In fact, due to the effectiveness of anti-lock braking (ABS) on modern vehicles, which prevents tires from locking up, the Traction rating isn't as meaningful as it once was.
The "Temperature" rating is somewhat connected to the speed index, in that tires with a higher heat tolerance are capable of higher speeds, but its "A" rating is somewhat vague as it covers everything good for 115 mph or above.
The ratings, though made somewhat superfluous by today's tires, do provide additional details, but aren't required by law on many tires such as winter, light truck, and trailer tires.
What the Special Symbols on Tires Mean
Special symbols, such as the five-pointed star in this example, aren't just there for decoration. They differ between manufacturers and identify Original Equipment (OE) to make it easier to spot the right choice for replacement. It's also a tire that's been specifically tuned, by modifying its compound or construction, to offer a slight variation of sound, treadwear, ride, or handling for a specific model.
While you can fit a set of Michelin Pilot Alpin 5s to numerous Audi, Mercedes-Benz, and Porsche models, units with a five-pointed star are specifically designed for BMWs, such as the BMW M3 that we sampled them on. Other examples include Lamborghini's "L" or "L1", Pagani's "HP", Volkswagen's plus sign, GM's "TPC Spec", Porsche's "N0"/"N1"/"N2", and Mercedes-Benz's "M0".
How to Know if Your Tires Are Good for the Winter
Without getting too deep in the weeds on the difference between all-season, all-weather, summer, winter, all-terrain, and mud-terrain tires, know that there are specific seals of approval on whether a tire, no matter its category, can handle severe weather conditions.
You'll find "M+S" on just about every tire that isn't a summer tire, as its "Mud and Snow" approval simply denotes a tread design that has 25 percent open space. There's no testing involved to earn that label, so the performance of M+S tires can vary considerably depending on the surface and conditions.
In 1999, the three-peak mountain snowflake (3PMSF) badge was added as a more meaningful way to show that a tire has been specifically tested and shows improvement in acceleration and traction in winter conditions. This symbol can be found on many different segments of tires from all-weather rubber to knobby mud-terrains.
The newest evolution of winter traction is the snowy mountain peak or ice-grip symbol. This further differentiates tires designed specifically for severe weather by completing braking testing on an icy surface.
How to Read Directional Tires
Directional tires have a specific tread pattern where the tread blocks, grooves, and sipes are designed to roll in one direction. Sometimes designated with stampings reading "Inside" and "Outside," most directional tires show an arrow of rotation. For the sake of avoiding any confusion, understand that while a vehicle is moving forward, the wheels on the driver's side of the car are spinning counter-clockwise, while the wheels on the passenger side spin clockwise.
The other information shown in this example is an "E2" followed by three groups of numbers. This designation is used exclusively for the European Regulatory Authorities—meaning if you're reading this anywhere near Ohio, ignore it.
The number directly after "E" is the country code for where the approval was issued. E1 is Germany, E2 is France, E3 is Italy, and E4 is Netherlands. The list goes as far as E65 for Uganda. The "S2WR2" is another international rating required for approval for rolling resistance, sound, and wet grip.
What's the Maximum Pressure for My Tires?
Tires also have a recommended maximum air pressure (in psi) that—while somewhat useful—is only a small piece of information when it comes to knowing what pressure setting to use for your tires. Never use the max pressure rating on the sidewall to determine how much air to put into your tires. Instead, use the manufacturer's recommended information provided on the placard that's often found in the driver's door jamb of your car or in the owner's manual. Depending on the vehicle, this could mean the front or rear tires have different recommendations, and there are often different tire-pressure settings for differing loading conditions or when running at high speeds.
Some tires, like the one in this example, will include a list of basic information about their construction. This Michelin X-Ice (pictured above) shows its tread is a 4-ply made up of one polyester, two steel, and one polyamide. The sidewall is a single ply of polyester. It serves no other purpose than to appease car nerds, like us, who seek every bit of information for all things automotive, no matter how granular.
How to Tell Which Tires Are Quieter
The symbol and name will differ between tire manufacturers, but tires with noise-reducing technology typically wear a flashy logo with a fancy name. In this example, the Nokian pins the SilentDrive honorific to denote a tire featuring a tread design and materials that aim to greatly reduce road noise.
Pirelli Noice Cancelling System (PNCS) has a muted speaker symbol, Goodyear's SoundComfort Technology is a music note within a tire, but there is also Dunlop's Noise Shield Technology, Continental's ContiSlent, and Bridgestone's B-Silent, all with the same goal of making tires as quiet as possible, and many of which include a foam insert to block noise.
