March 9, 2026
Searching for the right set of tires is important to your vehicle’s performance. You may have seen a set of numbers on the side of your tires and wondered what they mean. We’re here to clear up some of the confusion and help you understand what these numbers mean and how they affect your ride. Let’s start with understanding tire size codes.
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Understanding Tire Size Codes
There are typically seven different sets of numbers and letters that make up the tire size code.
- Tire Type
- Tire Width
- Aspect Ratio
- Construction
- Rim Diameter
- Load Index
- Speed Rating
Example: P215/55 R17 94W
Tire Type
Let’s start with the tire type. Most tires will have a P at the start of their tire code, although sometimes this code is at the back. P stands for Passenger, whereas LS = Light Truck, ST = Special Trailer, T = Temporary, and M+S = Mud & Snow. This denotes what kind of work the tires are built for. Make sure you're buying the right tire type for your vehicle before you have them installed.
Tire Width
Next is tire width. Tire width is measured across the tire from inner to outer sidewall, not tire diameter. In our example above, 215, you can guess this represents the tire width in millimeters. Most passenger tires range from 165mm for compact cars to 255mm for larger vehicles (trucks and SUVs).
Aspect Ratio
The third number represents aspect ratio. Aspect ratio is the height of the sidewall compared to the tire’s width, measured from inner to outer sidewall. If a tire’s aspect ratio is 50, that means the height of the sidewall is equal to 50% of the tire’s width.
Another way to look at this is if the tire width is 200mm, and the aspect ratio is 50%, the sidewall height is 100mm. Aspect ratios are important to know how thick your wheel is, which can impact handling and performance, depending on how you apply your vehicle to specific driving conditions.
Tire Construction
Fourth is tire construction; how is it made? Typical construction codes you’ll find on your tire include:
- R for Radial: This construction type is the most common for passenger tires. Their plies run radially under the tread, delivering greater flexibility and durability. This is typical for all-season tires, offering better comfort, fuel efficiency, and balanced handling in all conditions.
- D for Bias-Ply:Typical for off-road tires, classic cars, and heavy-duty trucks, this tire type offers a cross-ply construction method. The plies run diagonally across the tire, forming a crossing pattern that creates a firm, robust tire construction, built for off-roading and heavy torque applications.
- B for Belted:Used for heavy-duty vehicles, belted tires have reinforcing layers called belts, typically made of steel or Aramid. These reinforced belts offer puncture resistance and stability for better grip and handling under the intense workload of heavy-duty vehicles.
Rim Diameter
Rim diameter is typically measured by inches in the U.S. So if we use the example above: P215/55 R17 94W, that means the rim diameter is 17 inches. You can measure this yourself on your rim by starting at the inside of the rim and measuring to the bead seat. That way you can know exactly what to expect when you’re looking for tires that fit your vehicle.
Next up are load index and speed rating. Let’s take a deeper look at what these mean and how they impact your tire’s performance.
Load Index and Speed Rating Explained
Load index and speed rating are important factors to consider when shopping for new tires. You should know how much your tires can take in terms of load capacity and their maximum speed so you can avoid overpowering your tires, which can result in a blowout.
The load index and speed ratings are the last two numbers on your tire’s sidewall. Load index is the first set of numbers, let’s start there.
Your load index represents the maximum weight a tire can carry at its maximum air pressure. The number on your sidewall has different meanings. If your tire has an 88 on the sidewall, it has a max capacity of 1,235 lbs per tire. The highest load index is 150, which translates to 7,385 lbs per tire.
Speed ratings are categorized by letters that you’ll see at the end of the tire code. These letters indicate the maximum speed these tires can handle. Most passenger vehicles will have speed ratings ranging from 120 mph to 186 mph.
What Each Sidewall Marking Means for Performance
The code on your tire’s sidewall translates to how your vehicle is going to perform in different driving conditions. Let’s start from the beginning. Your tire width will impact your vehicle’s handling ability. The wider the tread width, the more surface area you have to tackle curves.
The aspect ratio also impacts how thick your tire will be. This can impact tire durability, traction, and ride comfort. A lower aspect ratio typically gives the vehicle sharper steering, which is great for track applications. Providing more stability while cornering is a big advantage, but one of the drawbacks is the thinness of the tire, which makes it more susceptible to pothole damage and punctures. A higher aspect ratio provides more comfort, better absorbing road bumps and uneven surfaces.
Tire construction also impacts vehicle performance. Radial tires, the most common for passenger vehicles, have better grip, run cooler, and provide a more comfortable drive and a wide range of tread life. Bias-ply tires deliver strong load capacities and impact resistance for heavy duty vehicles that need to get the job done, without excuses.
Your tires’ load index is important for performance. The wrong load index can lead to overheating and increasing your chance of tire failure. Tires with a higher load index can enjoy greater stability and tire stiffness for greater durability.
The speed rating depicts the maximum speed your tires can perform under. This impacts vehicle handling, highway performance, and how hard you can push your tires without putting too much risk in a blowout.
Common Tire Code Mistakes to Avoid
Looking for the right tire for your vehicle is important so you can have peace of mind as you drive. Shopping for tires that cannot take the load or torque your vehicle delivers can lead to tire failures. Always check the load index if you have a heavy-duty vehicle to ensure that your tires can bear that weight.
Another common mistake people make when looking at the tire’s speed rating, they assume the speed ratings are in alphabetical order. We wish they were too, but they’re not. Here are some of the speed ratings organized by maximum speed.
- U = 124 mph
- H = 130 mph
- V = 149 mph
- W = 160 mph
- Y = 186 mph
- (Y) = 186+ mph
Mixing tire types on your vehicle is also bad for tire performance. This can lead to uneven tire wear, misalignment, and put extra pressure on your suspension. Always install a new set of tires, don’t mix and match to avoid these tire and suspension problems.
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