How to Read Tire Size Numbers on Your Tire
Your tire’s sidewall is full of important information that affects safety, comfort, fuel economy, and performance. While it may look confusing at first, every number and letter has a specific meaning. This guide explains tire size markings in plain English, with a focus on trucks, SUVs, and everyday driving in the United States.
This single line tells you almost everything you need to know about the tire.
1. Tire Class: P vs LT
The first letter indicates the type of vehicle the tire is designed for.
- P (Passenger) – Designed for cars, crossovers, and many SUVs. Prioritizes comfort, low noise, and fuel efficiency.
- LT (Light Truck) – Built for pickups, heavy SUVs, towing, and off-road use. These tires have stronger internal construction and stiffer sidewalls.
If you drive a truck like a Ford F-150, RAM 1500, or Chevy Silverado and regularly tow or haul, an LT tire is often recommended for better durability and control.
2. Section Width (275)
The section width is the tire’s width in millimeters, measured from sidewall to sidewall. In this example, 275 means the tire is 275 mm wide.
3. Aspect Ratio (65)
The aspect ratio represents the sidewall height as a percentage of the tire’s width. A 65 aspect ratio means the sidewall height is 65% of 275 mm.
Higher aspect ratios provide a smoother ride and better protection on rough roads, which is common on SUVs and trucks.
4. Tire Construction (R)
The letter R stands for Radial construction. Almost all modern tires are radial, meaning the internal cords run perpendicular to the direction of travel.
5. Wheel (Rim) Diameter (18)
This number tells you the diameter of the wheel in inches. An 18 means the tire fits only on an 18-inch rim. This measurement must match your wheel exactly.
6. Load Index (114)
The load index indicates how much weight each tire can safely carry. A load index of 114 means the tire can support approximately 2,601 lbs.
7. Speed Rating (T)
The speed rating shows the maximum speed the tire is designed to handle safely.
- S – up to 112 mph
- T – up to 118 mph
- H – up to 130 mph
8. DOT Code & Tire Age
The DOT code tells you where and when the tire was manufactured. The last four digits indicate the production date. Example: 3522 = 35th week of 2022.
Most experts recommend replacing tires after 6 years, regardless of tread depth.
9. M+S and 3PMSF Markings
- M+S – Mud and Snow (basic all-season capability)
- 3PMSF (Mountain Snowflake) – Certified for severe winter conditions
Why Understanding Tire Size Matters
Choosing the correct tire size ensures speedometer accuracy, safe braking, proper load capacity, and no clearance issues. Always follow your vehicle manufacturer’s recommended tire size.