How to Read Tire Size Numbers
What 225/65R17 actually means — decoded in plain English
What Those Numbers on Your Tire Sidewall Mean
Every tire has a string of numbers on its sidewall — something like 225/65R17 102H. Each part tells you something specific about the tire. Here's how to decode it.
The Full Breakdown: 225/65R17 102H
| Part | Meaning | Example |
|---|---|---|
| 225 | Section width in millimeters (widest point) | 225 mm wide |
| 65 | Aspect ratio — sidewall height as % of width | 65% of 225 = 146 mm tall sidewall |
| R | Radial construction (almost all modern tires) | — |
| 17 | Rim diameter in inches | Fits a 17-inch wheel |
| 102 | Load index (max weight each tire can carry) | 102 = 1,874 lbs per tire |
| H | Speed rating (max sustained speed) | H = 130 mph |
Section Width
The first number (225) is the tire's width in millimeters, measured from sidewall to sidewall at the widest point. A wider tire generally means more grip but can also affect fuel economy and handling feel.
Aspect Ratio
The second number (65) is the aspect ratio — the sidewall height expressed as a percentage of the width. A lower aspect ratio (like 45) means a shorter, stiffer sidewall and sportier handling. A higher aspect ratio (like 70) means a taller sidewall and a softer, more comfortable ride.
Rim Diameter
This must match your wheel size exactly. Installing a tire with the wrong rim diameter is impossible — the tire won't seat on the bead.
Why This Matters When Shopping
When replacing tires, always match the width, aspect ratio, and rim diameter to your original equipment (OEM) spec — or consult your owner's manual for approved alternates. Deviating too far can affect speedometer accuracy, ABS, and handling.
Frequently Asked Questions
Can I put a wider tire on my car?
Yes, within limits. Going one size wider (e.g., 235 instead of 225) is usually fine if the wheel width supports it. Going too wide can cause rubbing on the fender or suspension components. Always check manufacturer clearances.
What does P mean at the start of a tire size?
P stands for Passenger. It means the tire is designed for passenger cars. LT means Light Truck, which has a higher load rating and stiffer construction.
Do all four tires need to be the same size?
For most vehicles, yes. Mixing sizes can cause handling imbalances and put stress on differentials. Some performance cars use staggered fitment (wider rears), but this is intentional and specified by the manufacturer.