Use this calculator to compare your current tire size with a potential new size, ensuring compatibility and understanding the impact on your vehicle.
Understanding Wheel and Tire Sizes
Choosing the right wheels and tires is crucial for your vehicle's performance, safety, and aesthetics. This calculator helps you understand how changes in tire size affect key metrics like overall diameter, sidewall height, and speedometer readings.
How Tire Sizes Work
Tire sizes are typically represented by a series of numbers, like P225/55R17. This code breaks down as follows:
P: Indicates the tire is for Passenger vehicles.
225: Tire Width in millimeters (mm). This is the width of the tire from sidewall to sidewall.
55: Aspect Ratio. This is the height of the tire's sidewall as a percentage of its width. In this case, the sidewall height is 55% of the 225mm width.
R: Indicates Radial construction.
17: Wheel Diameter in inches. This is the diameter of the wheel the tire fits onto.
The Math Behind the Calculator
Our calculator uses these standard formulas to determine the overall tire diameter and compare sizes:
The calculator then compares the overall diameter of your current tire setup with the new one to show the difference in millimeters and as a percentage. This difference is important because:
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.
Odometer Accuracy: Similar to the speedometer, changes in tire diameter will affect the accuracy of your odometer readings.
Ground Clearance: A larger overall diameter can increase your vehicle's ground clearance, while a smaller one will decrease it.
Fitment: Significantly larger or smaller tires may rub against the fenders or suspension components, causing damage or affecting handling.
When to Use This Calculator
When considering upgrading your wheels and tires for a different look.
When replacing worn tires and exploring alternative sizes.
To ensure new tires will be compatible with your vehicle's existing setup and maintain speedometer accuracy.
To estimate changes in ground clearance.
Always consult your vehicle's owner's manual or a professional mechanic to ensure any tire size changes are safe and appropriate for your specific car model.
function calculateTireSize() {
var currentTireWidth = parseFloat(document.getElementById("currentTireWidth").value);
var currentAspectRation = parseFloat(document.getElementById("currentAspectRation").value);
var currentWheelDiameter = parseFloat(document.getElementById("currentWheelDiameter").value);
var newTireWidth = parseFloat(document.getElementById("newTireWidth").value);
var newAspectRation = parseFloat(document.getElementById("newAspectRation").value);
var newWheelDiameter = parseFloat(document.getElementById("newWheelDiameter").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = "; // Clear previous results
// Input validation
if (isNaN(currentTireWidth) || isNaN(currentAspectRation) || isNaN(currentWheelDiameter) ||
isNaN(newTireWidth) || isNaN(newAspectRation) || isNaN(newWheelDiameter)) {
resultDiv.innerHTML = 'Please enter valid numbers for all fields.';
return;
}
if (currentTireWidth <= 0 || currentAspectRation <= 0 || currentWheelDiameter <= 0 ||
newTireWidth <= 0 || newAspectRation <= 0 || newWheelDiameter <= 0) {
resultDiv.innerHTML = 'All input values must be positive.';
return;
}
// Calculate current tire dimensions
var currentSidewallHeightMM = currentTireWidth * (currentAspectRation / 100);
var currentOverallDiameterMM = (currentSidewallHeightMM * 2) + (currentWheelDiameter * 25.4);
// Calculate new tire dimensions
var newSidewallHeightMM = newTireWidth * (newAspectRation / 100);
var newOverallDiameterMM = (newSidewallHeightMM * 2) + (newWheelDiameter * 25.4);
// Calculate differences
var diameterDifferenceMM = newOverallDiameterMM – currentOverallDiameterMM;
var diameterDifferencePercentage = (diameterDifferenceMM / currentOverallDiameterMM) * 100;
// Display results
var outputHTML = 'Comparison Results';
outputHTML += 'Current Tire Diameter: ' + currentOverallDiameterMM.toFixed(2) + ' mm (Sidewall: ' + currentSidewallHeightMM.toFixed(2) + ' mm)';
outputHTML += 'New Tire Diameter: ' + newOverallDiameterMM.toFixed(2) + ' mm (Sidewall: ' + newSidewallHeightMM.toFixed(2) + ' mm)';
outputHTML += 'Difference: ' + diameterDifferenceMM.toFixed(2) + ' mm ';
if (diameterDifferencePercentage >= 0) {
outputHTML += '(+' + diameterDifferencePercentage.toFixed(2) + '%)'; // Warning color for increase
} else {
outputHTML += '(' + diameterDifferencePercentage.toFixed(2) + '%)'; // Danger color for decrease
}
outputHTML += '(Changes affect speedometer, odometer, and ground clearance)';
resultDiv.innerHTML = outputHTML;
}