How Do You Tell The Size Of A Tire - Complete Guide
How Do You Tell The Size Of A Tire - Complete Guide
Knowing how to tell the size of a tire is essential for every vehicle owner. Whether you're purchasing new tires, checking compatibility, or simply want to understand your current setup better, reading the tire size is a fundamental skill. This comprehensive guide will walk you through everything you need to know about determining tire size and understanding what those numbers and letters actually mean.
Where to Find Your Tire Size
The first step in learning how to tell the size of a tire is knowing where to look. There are three primary places you can find your tire size:
- The tire sidewall - The most direct source is the tire itself. The tire size is molded into the sidewall of every tire.
- Vehicle door jamb - Most vehicles have a sticker on the driver's side door jamb that lists the recommended tire size.
- Owner's manual - Your vehicle's manual will specify the manufacturer-recommended tire size.
For the most accurate and current information, always check the tire size directly from the sidewall of your existing tires.
Reading Tire Size on the Sidewall
The tire size on the sidewall appears as a series of numbers and letters. For example, a common tire size might be P215/65R16 95H. Let's break down what each part means:
P - Tire Type
The first letter indicates the type of tire:
- P: Passenger vehicle
- LT: Light Truck
- ST: Special Trailer
- T: Temporary (spare)
- No letter: European metric sizing
215 - Tire Width
The first number in the tire size (215 in our example) represents the width of the tire in millimeters, measured from sidewall to sidewall. A wider tire size generally offers better grip but may reduce fuel economy.
65 - Aspect Ratio
The number after the slash in the tire size is the aspect ratio or profile. It tells you the height of the tire's sidewall as a percentage of the tire's width. In our example, the sidewall height is 65% of the tire width (215mm). Lower profile tires (smaller numbers) generally offer better handling but a harsher ride.
R - Construction Type
The letter after the aspect ratio in the tire size indicates the internal construction of the tire:
- R: Radial construction (most common)
- D: Diagonal or bias ply construction
- B: Belted bias construction
16 - Wheel Diameter
This number in the tire size indicates the diameter of the wheel (rim) in inches that the tire is designed to fit. In our example, this tire fits a 16-inch wheel.
95 - Load Index
The number after the wheel diameter in the tire size is the load index, which indicates how much weight the tire can support when properly inflated. Higher numbers mean higher capacity.
H - Speed Rating
The final letter in the tire size is the speed rating, indicating the maximum speed the tire can handle safely. For example, H means the tire is rated for speeds up to 130 mph.
Special Tire Size Formats
When learning how to tell the size of a tire, you'll encounter different formatting for special applications:
Metric Sizing (Euro-Metric)
A metric tire size might look like 215/65R16 95H (without the P prefix). This is common on European vehicles and indicates a slightly higher load capacity than P-metric tires.
Light Truck (LT) Sizing
LT tire sizes are formatted like LT245/75R16 120/116S. The dual load indices indicate the tire's capacity in single and dual configurations.
Flotation Sizing
For off-road applications, you might see tire sizes like 33x12.5R15, indicating:
- 33: Overall diameter in inches
- 12.5: Width in inches
- R15: Radial construction, 15-inch wheel diameter
How to Tell if You Have the Right Tire Size
To determine if you have the correct tire size for your vehicle:
- Check the manufacturer's recommended tire size in the owner's manual or door jamb sticker
- Ensure all four tires have the same tire size (unless your vehicle specifies different sizes for front and rear)
- Verify that the load index meets or exceeds the minimum required for your vehicle
If you're considering changing your tire size, be aware that significant deviations from the original specifications can affect:
- Speedometer accuracy
- Vehicle handling
- Fuel economy
- Clearance with vehicle components
For a quick way to compare different tire sizes or calculate the effects of changing your tire size, try our tire calculator.
Tire 1
Tire 2
Reading Additional Tire Information
Besides the main tire size designation, the sidewall contains other important information:
DOT Code
The Department of Transportation (DOT) code indicates when and where the tire was manufactured. The last four digits indicate the week and year of manufacture (e.g., 1220 means the 12th week of 2020).
UTQG Rating
The Uniform Tire Quality Grading system rates tires on:
- Treadwear: A comparative rating for tread longevity
- Traction: Rated from AA (highest) to C (lowest)
- Temperature: Rated from A (highest) to C (lowest)
Maximum Pressure and Load
Every tire sidewall displays the maximum inflation pressure and maximum load capacity, both critical for safe operation.
Common Questions About Tire Size
Can I use a different tire size than what's recommended?
While minor variations in tire size may be acceptable, significant changes can affect vehicle performance and safety. Always consult with a tire professional if you're considering a different tire size.
How do plus-sizing and minus-sizing work?
Plus-sizing involves increasing the wheel diameter while decreasing the sidewall height to maintain a similar overall tire size. Minus-sizing does the opposite. Both require careful calculation to ensure proper fitment.
How does tire size affect performance?
Different tire sizes can significantly impact:
- Handling: Wider tires generally offer better grip
- Comfort: Taller sidewalls (higher aspect ratios) usually provide a smoother ride
- Fuel economy: Larger, wider tires typically reduce efficiency
- Speed capability: Varies with the speed rating of the tire
Conclusion
Understanding how to tell the size of a tire is an important skill for all vehicle owners. By learning to read the tire size markings on your sidewall, you can make informed decisions about replacements, upgrades, and maintenance. Remember that your vehicle's performance, safety, and efficiency all depend on having the right tire size.
For help comparing different tire sizes or calculating the effects of changes, use our tire size calculator tool, which can show you the differences in diameter, circumference, and speedometer accuracy between different tire sizes.
Additional Resources
- Tire Pressure Guidelines
- Comparing Different Tire Sizes
- Understanding Rim Width and Tire Size
- Converting PSI to Bar
Published: August 17, 2025