What Is a Tire Size Calculator?
This calculator compares two tire sizes (using standard notation like 225/60R16) to show the resulting diameter difference — useful when considering a different tire or wheel size, since a significant size change affects your speedometer accuracy and ground clearance.
How to Use the Tire Size Calculator
- Enter your original tire size (width/aspect ratio/rim diameter).
- Enter the new tire size you're considering.
- View the diameter difference and speedometer impact.
Tire Size Formula
Worked Example
Original: sidewall = 225×0.60 = 135mm; diameter = 16 + (2×135/25.4) ≈ 26.63 in
New: sidewall = 235×0.55 = 129.25mm; diameter = 17 + (2×129.25/25.4) ≈ 27.18 in
Difference: approximately +2.1%
Understanding Your Results
Tire experts generally recommend keeping overall diameter within about 3% of the original size to avoid significant speedometer inaccuracy, clearance issues, or handling changes. A larger new diameter means your speedometer will read slower than your actual speed (and vice versa for a smaller diameter).
Common Mistakes to Avoid
- Choosing a significantly different tire diameter without checking for wheel well clearance issues.
- Ignoring speedometer recalibration needs after a significant tire size change.
Frequently Asked Questions
225 is the tire width in millimeters, 60 is the aspect ratio (sidewall height as a percentage of width), R indicates radial construction, and 16 is the wheel rim diameter in inches.
A common guideline suggests staying within about 3% of the original overall diameter to minimize speedometer error, clearance issues, and handling changes.
Yes — a larger overall diameter causes your speedometer to under-read your actual speed, while a smaller diameter causes it to over-read, since the speedometer calculates speed based on wheel rotations.
It's the tire's sidewall height expressed as a percentage of its width — a lower aspect ratio means a shorter, stiffer sidewall (common in performance tires).
You should generally stay within manufacturer-recommended size ranges and verify wheel well clearance — significant deviations can affect handling, speedometer accuracy, and even void warranties.