How to Read Tire Size: Every Sidewall Number Explained

A tire size code like P205/65R15 94H packs seven separate pieces of information into one string. Decoded: it is a passenger tire (P), 205 mm wide, with a sidewall 65% as tall as it is wide, of radial construction (R), built for a 15-inch wheel, rated to carry up to 1,477 lb per tire (load index 94), at speeds up to 130 mph (speed rating H). Every passenger-car tire sold in North America uses this same format.

Take the example code P205/65R15 94H. Here is what each piece means at a glance:

The format is the same on every passenger-car tire sold in North America. Only the values change with the vehicle.

Before the width number you will often see a letter. It tells you what kind of vehicle the tire is built for:

• P — Passenger. Standard car, SUV, and crossover tires. The most common type by far.
• LT — Light Truck. Stronger sidewalls for heavier loads and towing. Found on most 1/2-ton, 3/4-ton, and 1-ton pickups.
• ST — Special Trailer. Stiff sidewalls, never for use on a steered axle. Trailer applications only.
• T — Temporary. The donut spare in your trunk. Limited to about 50 mph and short distances.
• (no letter) — Euro-metric. Same physical dimensions as a P-metric tire but rated for slightly higher load. Common on European cars and many newer crossovers.

An important catch: a passenger (P) tire and a light truck (LT) tire of the same nominal size, say 265/70R17, are not interchangeable. The LT carries more weight but rides stiffer. The P will overload if you put it on a truck that calls for LT. Always match the service type your vehicle calls for.

Section width is the first three-digit number. It is the width of the tire from sidewall to sidewall, in millimeters. A 205 tire is roughly 205 mm (about 8.1 inches) wide. Wider tires give more grip and a planted feel, but also more rolling resistance, more road noise, and more weight. Most factory-recommended widths balance handling against fuel economy.

Aspect ratio is the number right after the slash. It is the sidewall height expressed as a percentage of the section width. A 205/65 tire has a sidewall that is 65% of 205 mm, or about 133 mm (5.2 inches) tall. Higher aspect ratios (65, 70, 75) mean taller sidewalls, softer rides, and more comfortable off-road performance. Lower aspect ratios (35, 40, 45) mean shorter sidewalls, sharper handling, better cornering, but harsher rides and more vulnerability to potholes. That is why sports cars run something like 245/35R20 with almost no sidewall, and trucks run 265/70R17 with lots of it.

Construction code is the letter after the aspect ratio. R means radial — nearly every modern tire. B means bias-belted, older and rarely on new passenger cars. D or a hyphen means diagonal/bias-ply, mostly trailer and specialty. If you see R, that is normal. Anything else means you are shopping for a specialty application.

Wheel diameter is the last number in the size code. It tells you the size of the wheel (rim) the tire fits, in inches. A "15" means a 15-inch wheel. Tire and wheel diameters must match exactly — you cannot put a 16-inch tire on a 15-inch wheel.

The load index is a code that maps to a maximum weight the tire can safely carry, per tire, at maximum inflation pressure. Higher index = more weight capacity. Common values:

Multiply the per-tire weight by four to get the vehicle's maximum loaded weight at that tire spec. If your truck weighs 7,200 lb fully loaded, you need a load index of at least 100 (4 × 1,764 = 7,056 lb — barely enough), or preferably higher for margin. Never go below your factory load index. Going higher is fine; going lower is unsafe.

The speed rating letter at the end of the size tells you the maximum sustained speed the tire can handle while carrying its rated load. Even if you will never drive 130 mph, the rating reflects how heat-resistant and well-built the tire is.

Most regular passenger vehicles run H or T. Never go below your factory speed rating. Going higher is fine; going lower can compromise heat tolerance even at normal highway speeds.

Look elsewhere on the sidewall for a code like Treadwear 600 Traction A Temperature B. That is the UTQG (Uniform Tire Quality Grading) rating, required by the DOT on passenger tires.

• Treadwear — a relative durability score. Higher = longer-lasting. A 600-rated tire should last roughly twice as long as a 300-rated one, but each manufacturer sets the scale against their own reference tire, so cross-brand comparisons are rough.
• Traction — wet grip when braking in a straight line. AA is the best, then A, then B, then C. Stick to A or higher.
• Temperature — heat dissipation at sustained speed. A is best, then B, then C. C-rated should only be a deliberate trade-off, not the default for a daily driver.

UTQG numbers do not appear on light-truck (LT), winter, or trailer tires — only on passenger.

On the sidewall you will see "DOT" followed by a string of characters and a four-digit number. That four-digit number is the manufacture date: the first two digits are the week of the year, the last two are the year.

For example, DOT XXXXXX 1024 means the tire was built in week 10 of 2024 — late February 2024.

Do not buy tires more than about three years old. Even if they look brand new, rubber compounds harden as they sit and grip suffers. A tire that has been on a warehouse shelf since 2022 will not perform like one molded last month, even at full tread. Always check the DOT code when you receive a new set, and reject anything older than three years.

Most tires use the millimeter-based metric system shown above. But you may also see other systems:

• Flotation sizing like 33×12.50R15. That reads as 33 inches tall by 12.5 inches wide on a 15-inch wheel. Used heavily for off-road and lifted truck tires.
• Hard-metric without service letter like 205/55R16. Common on European cars; same as P-metric but rated for slightly higher load at the same pressure.

Both are valid systems — just different ways of describing the same physical dimensions.

Three places, in order of reliability:

1. The driver's-side door jamb sticker. Open the door and look on the body or door edge for a metal or paper plate. It lists the original tire size, recommended pressures, and load info.
2. The owner's manual. Usually in the "Specifications" or "Tires" section.
3. The current tires on the car. Caveat: they may have been changed from factory spec by a previous owner.

Always trust the door jamb sticker over what is currently mounted. The sticker reflects what the manufacturer engineered the vehicle for — load index, speed rating, and pressure all worked out for that exact car.

1. Mixing sizes on the same axle. Both tires on the front or both on the rear must be the same size, brand, and ideally close in age. AWD and 4WD vehicles often require all four tires to match within tread-depth specs.
2. Going below the factory load or speed rating. Both indicate the tire's build quality for your vehicle's weight and intended use.
3. Ignoring the DOT date code. Looks new is not the same as is new.
4. Assuming P and LT are interchangeable. They are not. Match the service type to what your vehicle calls for.
5. Buying for looks alone. Wider or lower-profile tires might look great but can rub fenders, throw off your speedometer, harm fuel economy, and crack rims on potholes.

A few specific tires that match common factory sizes, in case you are shopping right now:

• 205/65R15 94H — many compact sedans (Civic, Corolla, Sentra). Try the Hercules Roadtour Connect AS All-Season.
• 225/60R17 99H — midsize sedans and crossovers (Camry, Accord, RAV4). Look at the Sailun Atrezzo SH408 in this size.
• 225/65R17 102H — midsize SUVs (CR-V, Outback). The Nexen N Priz AH5 is a strong value option.
• 265/70R17 115T — most 1/2-ton trucks and SUVs (F-150, Silverado, Tahoe). Browse our 17-inch truck tire selection.
• 245/40R18 97W — sport sedans and performance coupes. Make sure speed rating matches what the OEM specified.

Always confirm your specific size from your door jamb before ordering — wrong size means wrong fit, no exceptions. If your car is plus-sized from factory (different sizes front and rear), make sure to order each set separately.