Tyre Diameter Calculator

Tyre Diameter Calculator

function calculateTyreDiameter() { var tyreWidth = parseFloat(document.getElementById('tyreWidth').value); var aspectRatio = parseFloat(document.getElementById('aspectRatio').value); var rimDiameter = parseFloat(document.getElementById('rimDiameter').value); if (isNaN(tyreWidth) || isNaN(aspectRatio) || isNaN(rimDiameter) || tyreWidth <= 0 || aspectRatio <= 0 || rimDiameter <= 0) { document.getElementById('sidewallHeightInches').innerHTML = 'Sidewall Height: Invalid input. Please enter positive numbers.'; document.getElementById('sidewallHeightMM').innerHTML = "; document.getElementById('totalDiameterInches').innerHTML = 'Total Tyre Diameter: — inches'; document.getElementById('totalDiameterMM').innerHTML = 'Total Tyre Diameter: — mm'; return; } // Constants var MM_PER_INCH = 25.4; // Calculate sidewall height var sidewallHeightMM = tyreWidth * (aspectRatio / 100); var sidewallHeightInches = sidewallHeightMM / MM_PER_INCH; // Calculate total tyre diameter var totalDiameterInches = (2 * sidewallHeightInches) + rimDiameter; var totalDiameterMM = totalDiameterInches * MM_PER_INCH; // Display results document.getElementById('sidewallHeightInches').innerHTML = 'Sidewall Height: ' + sidewallHeightInches.toFixed(2) + ' inches'; document.getElementById('sidewallHeightMM').innerHTML = 'Sidewall Height: ' + sidewallHeightMM.toFixed(2) + ' mm'; document.getElementById('totalDiameterInches').innerHTML = 'Total Tyre Diameter: ' + totalDiameterInches.toFixed(2) + ' inches'; document.getElementById('totalDiameterMM').innerHTML = 'Total Tyre Diameter: ' + totalDiameterMM.toFixed(2) + ' mm'; } // Run calculation on page load with default values window.onload = calculateTyreDiameter;

Understanding Your Tyre's Diameter

The overall diameter of your vehicle's tyres is a critical measurement that impacts several aspects of its performance, safety, and even legal compliance. From speedometer accuracy to suspension clearance and gearing, knowing your tyre's exact diameter is essential, especially when considering a change in tyre size.

How to Read Tyre Sizes

Tyre sizes are typically displayed in a standardized format, such as 205/55R16. Let's break down what each part means:

• 205: This is the Tyre Width in millimeters (mm). It measures the width of the tyre from sidewall to sidewall.
• 55: This is the Aspect Ratio, expressed as a percentage. It represents the sidewall height as a percentage of the tyre's width. In this example, the sidewall height is 55% of 205mm.
• R: This indicates the tyre's construction type, with 'R' standing for Radial, which is the most common type today.
• 16: This is the Rim Diameter in inches. It specifies the diameter of the wheel that the tyre is designed to fit.

Why Tyre Diameter Matters

Changing your tyre's overall diameter, even by a small amount, can have significant consequences:

• Speedometer Accuracy: Your vehicle's speedometer is calibrated based on the original tyre diameter. A larger or smaller diameter will cause your speedometer to read inaccurately, potentially leading to speeding tickets or misjudging your actual speed.
• Odometer Reading: Similarly, the odometer will also be affected, leading to incorrect mileage readings.
• Gearing and Performance: A larger diameter tyre effectively changes your vehicle's final drive ratio, making it feel like you have "taller" gears. This can reduce acceleration and potentially impact fuel economy. Conversely, smaller tyres can make gears feel "shorter."
• Suspension and Fender Clearance: Larger tyres might rub against your vehicle's suspension components or fender wells, especially during turns or when the suspension compresses.
• ABS/Traction Control: Modern vehicles rely on wheel speed sensors for systems like ABS and traction control. Significant changes in tyre diameter can confuse these systems, leading to malfunctions.

How the Tyre Diameter Calculator Works

Our calculator uses the standard tyre sizing information to determine the total diameter. Here's the formula:

1. Calculate Sidewall Height: The sidewall height is calculated by multiplying the tyre width by the aspect ratio percentage. For example, if the width is 205mm and the aspect ratio is 55%, the sidewall height is 205mm * (55/100) = 112.75mm.
2. Convert Sidewall Height to Inches: Since the rim diameter is in inches, we convert the sidewall height from millimeters to inches (1 inch = 25.4 mm). So, 112.75mm / 25.4 = 4.44 inches.
3. Calculate Total Diameter: The total tyre diameter is the sum of the rim diameter plus twice the sidewall height (because there's a sidewall above and below the rim). So, 16 inches (rim) + (2 * 4.44 inches) = 24.88 inches.

The calculator provides both the sidewall height and the total tyre diameter in both inches and millimeters for your convenience.

Using the Calculator

Simply input the three key values from your tyre size:

1. Tyre Width (mm): The first number in the tyre size (e.g., 205).
2. Aspect Ratio (%): The second number (e.g., 55).
3. Rim Diameter (inches): The last number after the 'R' (e.g., 16).

Click "Calculate Tyre Diameter" to instantly see the results. This tool is invaluable for anyone planning to change tyre sizes, ensuring you make an informed decision that maintains your vehicle's integrity and performance.