How to Read Tire Size Codes: A Complete Guide
What Do Those Numbers on Your Tire Actually Mean?
If you've ever looked at the sidewall of a tire and seen something like 225/65R17 102H, you're not alone in wondering what it all means. Tire size codes are actually a straightforward system once you know how to decode them — and understanding them helps you buy the right tires with confidence.
Breaking Down the Tire Size Code
The First Number: Section Width
The first number (e.g., 225) is the tire's section width in millimeters — the distance from one sidewall to the other when the tire is mounted and inflated. A larger number means a wider tire.
The Second Number: Aspect Ratio
The number after the slash (e.g., 65) is the aspect ratio — the height of the tire's sidewall as a percentage of its width. So a 225/65 tire has a sidewall height that's 65% of 225mm, which is about 146mm tall. Lower numbers mean a lower-profile, sportier look; higher numbers mean more sidewall cushion and a smoother ride on rough roads.
The Letter: Construction Type
The letter R stands for Radial, which is the construction method used in virtually all modern passenger and light truck tires. You may occasionally see D (Diagonal/Bias-ply) on trailer or specialty tires.
The Rim Diameter
The next number (e.g., 17) is the diameter of the wheel rim in inches that the tire is designed to fit. This must match your vehicle's wheel size exactly.
Load Index
The number following the rim diameter (e.g., 102) is the load index — a code that tells you the maximum weight each tire can support. A load index of 102 = 1,874 lbs per tire. Always match or exceed your vehicle's required load rating.
Speed Rating
The final letter (e.g., H) is the speed rating, indicating the maximum sustained speed the tire is designed for. Common ratings include:
- S – Up to 112 mph
- T – Up to 118 mph
- H – Up to 130 mph
- V – Up to 149 mph
- W – Up to 168 mph
Light Truck Prefix: LT vs P
Some tires start with a letter prefix. P (e.g., P225/65R17) means Passenger car tire. LT (e.g., LT265/70R17) means Light Truck — these are heavier-duty tires built for trucks, SUVs, and vehicles that tow or carry heavy loads. If your vehicle is a truck or SUV, make sure you're buying the right category.
Where to Find Your Correct Tire Size
Your correct tire size is listed in three places: the sticker inside your driver's door jamb, your owner's manual, and the current tires on your vehicle. Never go off memory alone — always verify before ordering.
Shop Tires by Type
Now that you can read a tire code, find the right tires for your vehicle: