How to Determine Tire Size and Type for Your Vehicle

If you’ve ever glanced at the side of your tire, you’ve seen a long string of numbers and letters - something like P215/65R15 95H. At first sight, it may seem confusing. Let Autoland Jax technicians help you to determine your tire's information.

Tire markings provide details on their dimensions, construction, and capabilities, including width in millimeters, aspect ratio (which is the tire’s sidewall height as a percentage of its width), construction type (where ‘R’ signifies radial), and the rim diameter in inches.

Following these are the Load Index (weight capacity) and Speed Rating (max speed).

The initial pair of numbers signifies the week of production.

On most tires, you’ll see a sequence like P235/75R15 or LT195/60R14. Each piece of this code tells you something specific.

1. P or LT at the beginning
2. P = Passenger car tire
3. LT = Light truck tire (pickups, some SUVs)
4. First number (235). This is the tire width in millimeters, measured from sidewall to sidewall.
5. Second number (75). This is the aspect ratio: the sidewall height expressed as a percentage of the tire's width. Higher numbers mean taller sidewalls, which usually give a softer, more comfortable ride.
6. Letter in the middle (R)
7. R = Radial construction (the modern standard on most vehicles)
8. Last number (15). This is the wheel (rim) diameter in inches. Your tire must match your wheel size exactly.

Even if the rim diameter remains the same, small differences in width and aspect ratio can alter the overall tire height. That can lead to clearance issues, speedometer errors, or difficulty mounting the tire, so it’s always best to match the size recommended on your door jamb label or owner’s manual.

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Alternative tire marking style (31x10.5R15)

You may also see a different style, such as 31x10.5R15, often used for trucks and off-road tires.

1. 31 – Overall outer diameter of the tire in inches
2. 10.5 – Tire width in inches
3. R – Radial construction
4. 15 – Wheel diameter in inches

This format is common on lifted trucks, off‑road builds, and some specialty applications. The same rules apply: even if the rim size matches, make sure height and width won’t cause rubbing or steering issues.

Reading tire numbers: extra letters and symbols on the sidewall

Beyond size, sidewall markings tell you how the tire is built and where it performs best. Here are some of the most common you’ll see in Florida:

1. XL or Extra Load

Denotes a reinforced tire built to handle greater weight loads than a standard tire of identical size. The load index number will be higher, allowing more pounds per tire.

1. M+S or M&S (Mud and Snow)

Usually means the tire is all‑season or intended to handle light mud and slush. Many SUV and truck tires carry this symbol. It does not automatically mean true winter performance.

1. AS or All Season

Designed for year‑round use in mild climates like North Florida, handling rain and dry roads but not extreme snow and ice.

1. Snowflake/mountain symbol

This indicates a dedicated winter tire that meets a specific snow‑traction standard. If your tire doesn’t have this symbol, it is not a true winter tire.

1. Rain / Aqua / Water wording or umbrella icon

Marketing terms that usually point to a tread design optimized for wet traction and hydroplaning resistance.

1. Outside / Inside

Found on asymmetric tires. They must be mounted with the “Outside” side facing out. Mounting them incorrectly can hurt handling, braking, and tire wear.

1. RSC, RunFlat, or branded run‑flat names

These tires are built to be driven a limited distance at reduced speed after a pressure loss. Typically, they allow around 30–90 miles of driving at up to about 50 mph, depending on brand and model.

1. Rotation arrow or directional arrow

Shows the direction the tire should rotate. Directional tires must be mounted so that the arrow points forward when the car is moving.

1. Max Pressure

The maximum cold inflation pressure the tire is designed to handle, not necessarily the pressure you should run every day. Use the pressure on your door label unless a professional tells you otherwise.

1. Max Load

The maximum weight that a tire can safely support when used at the specified pressure.

Load index: How much weight a tire can carry

The load index is a number that corresponds to how many pounds a tire can safely carry. You’ll find it after the main size, often right before the speed rating (for example, 95H).

Below is a simplified load index table you can use as a quick reference:

Always buy a tire with a load index that meets or exceeds the original equipment rating. Dropping below that can be unsafe, especially if you tow, haul, or carry passengers often.

Determine speed rating: how fast the tire is designed to go

Right after the load index, you’ll see a letter that represents the speed rating. This indicates the maximum sustained speed the tire is designed to handle under proper conditions.

Speed ratings range from M (max speed 81 mph) to Y (max speed 186 mph).

You don’t need race‑car ratings for everyday Jacksonville driving, but you should never go above the speed rating specified by your vehicle’s manufacturer.