Tire Size Calculator
Compare two tire sizes and instantly see the difference in diameter, speedometer accuracy, ground clearance, and whether they'll fit your vehicle.
Quick Presets
Fitment Analysis
Individual Tire Stats
Current Stats
New Stats
Visual Comparison
Visual Size Comparison
How Tire Size Comparison Works
📐 Understanding Tire Numbers
A tire marked 265/70R17 means: 265mm wide, 70% aspect ratio (sidewall is 70% of width), fits a 17-inch rim. The overall diameter is calculated from these three numbers.
🎯 Speedometer Error
A larger tire travels further per revolution, making your speedometer read lower than actual speed. A smaller tire does the opposite. Our tool shows the exact mph offset.
🔧 Fitment Thresholds
Under 3% diameter difference = direct fit. 3–5% = may need minor trimming. 5–8% = lift kit recommended. Over 8% = major modifications required for safe operation.
⚡ Ground Clearance
Ground clearance increases by half the diameter difference. A tire 1 inch larger in diameter gives you 0.5 inches of extra ground clearance — great for off-road use.
How to Read Tire Sizes
Understanding how to read tire sizes is essential for anyone looking to replace or upgrade their vehicle's tires. The sequence of numbers and letters on the sidewall of a tire might look like a complex code, but it provides detailed information about the tire's dimensions, construction, and performance capabilities.
Whether you are using a tire size calculator for an exact match or exploring new tire fitment options for an off-road setup, knowing what these specifications mean will help you make an informed decision. A tire's size impacts everything from driving comfort and fuel economy to handling and speedometer accuracy.
What Does 265/70R17 Mean?
Let's break down a very common truck and SUV tire size: 265/70R17.
- 265 (Section Width): The first number represents the width of the tire in millimeters from sidewall to sidewall. In this case, the tire is 265mm wide.
- 70 (Aspect Ratio): This is the ratio of the tire's sidewall height to its width. A 70 means the sidewall height is equal to 70% of the 265mm width. A taller sidewall typically offers a smoother ride and better off-road capability.
- R (Construction): The "R" stands for Radial tire construction, which is the industry standard for almost all passenger and light truck tires today.
- 17 (Wheel Diameter): This indicates that the tire is designed to fit a 17-inch wheel or rim. If you upgrade to an 18-inch wheel, you would need a tire ending in 18.
When you use our wheel size calculator, you can instantly see how changing the aspect ratio (like going from a 70 to a 75) alters the overall tire diameter, potentially leading to clearance issues or speedometer inaccuracies.
Why Tire Size Matters for Fitment
Proper tire fitment is critical for the safety and performance of your vehicle. Upgrading to larger tires can improve ground clearance and give your truck or SUV a more aggressive stance, but it comes with potential drawbacks if you don't calculate the differences properly.
If a tire is too wide, it may rub against suspension components or wheel wells during sharp turns. If it's too tall, it can restrict suspension travel and throw off your vehicle's gearing and speedometer synchronization. That's why running your proposed tire sizes through a reliable tire comparison tool is heavily recommended before making a purchase.
Always remember to check your vehicle's owner manual and consult with suspension specialists if you plan to drastically alter your wheel diameter or overall rolling circumference.