What Do the Numbers on Tires Mean? A Guide to Understanding Tire Sizes
Ever noticed the string of letters and numbers printed on the side of your tires and wondered what they mean? Understanding tire sizes is essential for proper vehicle maintenance, improving fuel efficiency, and avoiding awkward moments when your mechanic or tire technician asks what kind of tires you’re looking for.
At Cheema Auto, we make tire care simple. In this guide, we’ll break down exactly what the numbers and letters on your tires mean and why they matter for your car, truck, or SUV.
How to Read Tire Numbers: What Each Section Tells You
Tire numbers follow an industry-standard format and appear on the tire’s sidewall or inside the driver-side door sticker. These letters and numbers represent your tire type, width, aspect ratio, construction, diameter, load index, and speed rating.
1. Tire Type
The first letter on the tire identifies its type:
- P = Passenger vehicle tires (cars, SUVs, minivans, light-duty trucks)
- LT = Light Truck tires, made for heavy loads and rugged terrains
- ST = Special Trailer tires, designed for towed items like trailers and campers (not for drive axles)
- T = Temporary spare tires, meant only for short-term use
2. Tire Width
The next three-digit number tells you the tire width in millimeters, measured from sidewall to sidewall. For example, in “P215/65R15,” the tire width is 215 mm.
3. Aspect Ratio
Following the forward slash is the aspect ratio, which compares the sidewall height to the tire’s width as a percentage. For example, “65” means the sidewall height is 65% of the tire’s width. A higher number indicates a taller sidewall.
4. Tire Construction
The letter after the aspect ratio describes the tire’s internal construction:
- R = Radial tires (most common): built with overlapping layers of steel plies and strong fabric cords for durability
- D = Diagonal or bias-ply tires: older style with crisscrossing plies at an angle
- B = Belted bias tires: bias-ply tires reinforced with steel belts
5. Wheel Diameter
The next two-digit number shows the rim diameter in inches, which must match the wheel for a proper fit. For example, a “15” means the tire fits a 15-inch rim.
6. Load Index
The load index is a two- or three-digit number indicating how much weight the tire can safely carry when properly installed and inflated. Use a load index chart to find the weight in pounds that corresponds to the number on your tire.
7. Speed Rating
The final letter represents the maximum speed rating the tire can safely handle. While not an invitation to speed, it’s useful for performance comparison. A speed rating chart can help you understand what each letter means.
Other Important Tire Markings
- DOT Code: This series starts with “DOT” and confirms the tire meets national safety standards, while also identifying the manufacture date and location.
- UTQG Ratings: The Uniform Tire Quality Grading system rates tires for treadwear, traction, and temperature resistance, helping you choose a quality tire that suits your driving style and climate.
Why Knowing Tire Numbers Matters
Decoding your tire numbers can help you:
- Choose the right replacement tires
- Ensure proper load capacity and speed ratings
- Improve fuel efficiency and handling
- Avoid mismatches that could affect safety or performance
- Maintain correct rim and tire diameter compatibility
Need Help Choosing Tires? Cheema Auto Has You Covered
Still unsure about your tire numbers or which size fits your vehicle best? Bring your car, truck, or SUV to your local Cheema Auto automotive service center. Our tire professionals can inspect your tires, recommend replacements, and ensure they’re properly balanced, rotated, and ready for the road.
Schedule your tire inspection or replacement today with Cheema Auto your trusted partner in vehicle maintenance.
