Enter tire specifications for both tires to see the comparison.
Understanding Tire Diameter and Its Importance
The overall diameter of a tire is a critical measurement that affects your vehicle's speedometer accuracy, odometer readings, handling, fuel efficiency, and even the proper functioning of ABS and traction control systems. When changing tire sizes, it's essential to understand how the new tire's diameter compares to the original. This calculator helps you directly compare the overall diameters of two different tire configurations.
How Tire Diameter is Calculated
The overall diameter of a tire is determined by its width, aspect ratio, and rim diameter. The formula used is:
Overall Diameter = (Width in mm * Aspect Ratio / 100) * 2 / 25.4 + Rim Diameter in inches
Width (mm): The width of the tire in millimeters (e.g., 225mm).
Aspect Ratio (%): The sidewall height as a percentage of the tire's width (e.g., 55% means the sidewall height is 55% of the width).
Rim Diameter (inches): The diameter of the wheel rim the tire fits onto, measured in inches.
25.4: This is the conversion factor from millimeters to inches (1 inch = 25.4 mm).
The calculation first determines the sidewall height in millimeters by multiplying the width by the aspect ratio (divided by 100). This value is then multiplied by two (to account for both the top and bottom sidewalls) and converted to inches. Finally, the rim diameter in inches is added to get the total tire diameter.
Why Compare Tire Diameters?
Speedometer and Odometer Accuracy: If the new tire diameter is significantly larger than the original, your speedometer will read lower than your actual speed. Conversely, a smaller tire will make the speedometer read higher. The odometer will also be affected.
Vehicle Performance: Larger diameter tires can increase ground clearance but may also put more strain on the drivetrain and affect acceleration due to increased rotational mass. Smaller tires might improve acceleration but reduce ground clearance.
Electronic Systems: Modern vehicles rely on wheel speed sensors for ABS, traction control, and stability control. Significant variations in tire diameter can interfere with the correct functioning of these systems.
Fitment: Ensuring new tires fit within the vehicle's wheel wells without rubbing is crucial. Diameter is a primary factor in this clearance.
Using This Calculator
Simply input the width (in mm), aspect ratio (as a percentage), and rim diameter (in inches) for your two tire configurations. Click "Calculate Diameters" to see the calculated overall diameter for each tire and a direct comparison of the difference. This will help you make informed decisions when selecting new tires or understanding the implications of a tire size change.
function calculateTireDiameters() {
var tire1Width = parseFloat(document.getElementById("tire1Width").value);
var tire1AspectRatio = parseFloat(document.getElementById("tire1AspectRatio").value);
var tire1RimDiameter = parseFloat(document.getElementById("tire1RimDiameter").value);
var tire2Width = parseFloat(document.getElementById("tire2Width").value);
var tire2AspectRatio = parseFloat(document.getElementById("tire2AspectRatio").value);
var tire2RimDiameter = parseFloat(document.getElementById("tire2RimDiameter").value);
var resultsDisplay = document.getElementById("resultsDisplay");
resultsDisplay.innerHTML = "; // Clear previous results
if (isNaN(tire1Width) || isNaN(tire1AspectRatio) || isNaN(tire1RimDiameter) ||
isNaN(tire2Width) || isNaN(tire2AspectRatio) || isNaN(tire2RimDiameter)) {
resultsDisplay.innerHTML = 'Please enter valid numbers for all fields.';
return;
}
if (tire1Width <= 0 || tire1AspectRatio <= 0 || tire1RimDiameter <= 0 ||
tire2Width <= 0 || tire2AspectRatio <= 0 || tire2RimDiameter 0) {
diffClass += ' positive-diff';
diffText = `Tire 2 is ${difference_in.toFixed(2)}" (${difference_percentage.toFixed(2)}%) larger than Tire 1.`;
} else if (difference_in < 0) {
diffClass += ' negative-diff';
diffText = `Tire 2 is ${Math.abs(difference_in).toFixed(2)}"` + ` (${Math.abs(difference_percentage).toFixed(2)}%) smaller than Tire 1.`;
} else {
diffClass += ' neutral-diff'; // For zero difference, though unlikely with typical inputs
diffText = `Tire 1 and Tire 2 have the same diameter.`;
}
var resultsHTML = `