Choosing the right wheel and tire combination is crucial for vehicle performance, comfort, and aesthetics. This calculator helps you compare two different wheel and tire setups by calculating their overall diameter and identifying any significant differences. Understanding these differences is vital when considering upgrades or replacements for your vehicle.
How the Calculation Works
The overall diameter of a tire is determined by its rim diameter, tire width, and aspect ratio. The formula used in this calculator is as follows:
Tire Section Width (in mm): This is directly provided by the user (e.g., 225mm).
Aspect Ratio (%): This is the ratio of the tire's sidewall height to its section width, expressed as a percentage (e.g., 45%).
Tire Sidewall Height (in mm): Calculated as Tire Width (mm) * (Aspect Ratio / 100).
Tire Sidewall Height (in inches): Converted from millimeters to inches by dividing by 25.4 (since 1 inch = 25.4 mm).
Overall Tire Diameter (in inches): Calculated as Rim Diameter (inches) + 2 * Tire Sidewall Height (inches).
The calculator then compares the overall diameters of the two setups and indicates the difference in percentage.
Why Compare Wheel Sizes?
When you change your wheel size or tire profile, you're altering the overall diameter of the rotating assembly. This can have several consequences:
Speedometer Accuracy: A larger overall diameter will make your speedometer read lower than your actual speed, and a smaller diameter will make it read higher.
Gearing: A larger diameter effectively changes your final drive ratio, potentially affecting acceleration (making it slower) and fuel economy. A smaller diameter can improve acceleration but may decrease fuel economy at highway speeds.
Tire Clearance: Larger diameter tires might rub against the fender wells or suspension components, especially during turns or when the suspension is compressed.
Traction Control and ABS: These systems rely on consistent wheel speed readings. Significant variations in tire diameter can interfere with their proper functioning.
Ride Comfort: Lower aspect ratio tires (shorter sidewalls) generally provide a firmer ride, while higher aspect ratios offer more cushioning.
It's generally recommended to keep the overall diameter of your new wheel and tire setup as close as possible (within 1-3%) to your vehicle's original specifications to minimize negative impacts.
function compareWheels() {
var diameter1 = parseFloat(document.getElementById("diameter1").value);
var tireWidth1 = parseFloat(document.getElementById("tireWidth1").value);
var aspectRatio1 = parseFloat(document.getElementById("aspectRatio1").value);
var diameter2 = parseFloat(document.getElementById("diameter2").value);
var tireWidth2 = parseFloat(document.getElementById("tireWidth2").value);
var aspectRatio2 = parseFloat(document.getElementById("aspectRatio2").value);
var resultDiv = document.getElementById("comparisonResult");
var detailsDiv = document.getElementById("calculationDetails");
detailsDiv.innerHTML = ""; // Clear previous details
if (isNaN(diameter1) || isNaN(tireWidth1) || isNaN(aspectRatio1) ||
isNaN(diameter2) || isNaN(tireWidth2) || isNaN(aspectRatio2)) {
resultDiv.textContent = "Please enter valid numbers for all fields.";
resultDiv.style.color = "#dc3545"; // Red for error
return;
}
// Convert mm to inches for tire width
var tireWidthInches1 = tireWidth1 / 25.4;
var tireWidthInches2 = tireWidth2 / 25.4;
// Calculate sidewall height in inches
var sidewallHeight1 = tireWidthInches1 * (aspectRatio1 / 100);
var sidewallHeight2 = tireWidthInches2 * (aspectRatio2 / 100);
// Calculate overall diameter in inches
var overallDiameter1 = diameter1 + (2 * sidewallHeight1);
var overallDiameter2 = diameter2 + (2 * sidewallHeight2);
// Calculate percentage difference
var difference = overallDiameter2 – overallDiameter1;
var percentageDifference = (difference / overallDiameter1) * 100;
var resultText = "";
var color = "#28a745"; // Default to success green
if (Math.abs(percentageDifference) 0) {
resultText = "Wheel 2 is larger overall.";
} else {
resultText = "Wheel 1 is larger overall.";
}
resultText += " Difference: " + Math.abs(percentageDifference).toFixed(2) + "%";
if (Math.abs(percentageDifference) > 3) {
resultDiv.textContent = resultText + " (Significant difference!)";
color = "#dc3545"; // Red if significant difference
} else {
resultDiv.textContent = resultText;
}
resultDiv.style.color = color;
// Display calculation details
var detailsHTML = "Calculation Details:";
detailsHTML += "Wheel 1:";
detailsHTML += ` Tire Sidewall Height: ${sidewallHeight1.toFixed(2)} inches (${(sidewallHeight1 * 25.4).toFixed(2)} mm)`;
detailsHTML += ` Overall Diameter: ${overallDiameter1.toFixed(2)} inches`;
detailsHTML += "Wheel 2:";
detailsHTML += ` Tire Sidewall Height: ${sidewallHeight2.toFixed(2)} inches (${(sidewallHeight2 * 25.4).toFixed(2)} mm)`;
detailsHTML += ` Overall Diameter: ${overallDiameter2.toFixed(2)} inches`;
detailsHTML += `Difference: ${difference.toFixed(2)} inches (${percentageDifference.toFixed(2)}%)`;
detailsDiv.innerHTML = detailsHTML;
}