Tire on Wheel Calculator

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Tire Size & Wheel Fitment Calculator

Calculate total diameter, sidewall height, and circumference for any tire and wheel combination.

Sidewall Height: 0.00 in
Total Diameter: 0.00 in
Circumference: 0.00 in
Revs per Mile: 0.00

How to Calculate Tire Dimensions

When upgrading wheels or changing tires, it is crucial to understand the mathematical relationship between the tire width, aspect ratio, and wheel diameter. This "Tire on Wheel" calculator allows you to visualize how these numbers translate into the actual physical height and circumference of your setup.

Example Calculation:
Let's take a common tire size: 225/45 R17.

  • 225 is the width of the tire in millimeters.
  • 45 is the aspect ratio, meaning the sidewall height is 45% of the width.
  • 17 is the diameter of the wheel in inches.

The Math Behind the Tire

To find the total height (diameter) of the tire, we use the following steps:

  1. Calculate Sidewall Height: 225mm × 0.45 = 101.25mm.
  2. Convert to Inches: 101.25mm / 25.4 = 3.99 inches.
  3. Calculate Total Diameter: (3.99″ × 2) + 17″ = 24.98 inches.

Why Fitment Matters

Choosing the wrong tire size for your wheels can lead to several issues. If the total diameter changes significantly from the factory original, your speedometer will display an incorrect speed. A larger diameter means the car is actually moving faster than the gauge suggests. Additionally, tires that are too wide or too tall may rub against the fender liners or suspension components during tight turns or over bumps.

Standard vs. Metric Sizing

Most passenger vehicles use the metric system (P-Metric), but some off-road tires use flotation sizing (e.g., 33×12.50 R15). Our calculator focuses on the standard metric system found on 99% of modern cars. When selecting a new setup, try to stay within 3% of the original manufacturer's total diameter to ensure safety systems like ABS and Traction Control function correctly.

function calculateTireDimensions() { var width = parseFloat(document.getElementById("tireWidth").value); var ratio = parseFloat(document.getElementById("aspectRatio").value); var wheel = parseFloat(document.getElementById("wheelDiam").value); if (isNaN(width) || isNaN(ratio) || isNaN(wheel) || width <= 0 || ratio <= 0 || wheel <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // 1. Sidewall height in mm var sidewallMm = width * (ratio / 100); // 2. Sidewall height in inches var sidewallIn = sidewallMm / 25.4; // 3. Total diameter in inches (Wheel + 2x sidewall) var totalDiameter = wheel + (sidewallIn * 2); // 4. Circumference (D * Pi) var circumference = totalDiameter * Math.PI; // 5. Revolutions per mile (63,360 inches in a mile) var revsPerMile = 63360 / circumference; // Display results document.getElementById("resSidewall").innerText = sidewallIn.toFixed(2) + " in (" + sidewallMm.toFixed(1) + " mm)"; document.getElementById("resTotalDiam").innerText = totalDiameter.toFixed(2) + " in"; document.getElementById("resCircum").innerText = circumference.toFixed(2) + " in"; document.getElementById("resRevs").innerText = Math.round(revsPerMile).toLocaleString(); document.getElementById("tireResult").style.display = "block"; }

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