Tire Size Converter Calculator

Tire Size Converter Calculator

Conversion Results

Original Tire Specs

Sidewall Height: — mm

Overall Diameter: — inches

Circumference: — inches

Revolutions per Mile: —

New Tire Specs

Sidewall Height: — mm

Overall Diameter: — inches

Circumference: — inches

Revolutions per Mile: —

Comparison & Impact

Diameter Difference: — inches (—%)

Ground Clearance Change: — inches

Speedometer Reading (Original Speed: — mph):

If your speedometer reads — mph, your actual speed is — mph.

function calculateTireConversion() { var originalTireWidth = parseFloat(document.getElementById('originalTireWidth').value); var originalAspectRatio = parseFloat(document.getElementById('originalAspectRatio').value); var originalWheelDiameter = parseFloat(document.getElementById('originalWheelDiameter').value); var newTireWidth = parseFloat(document.getElementById('newTireWidth').value); var newAspectRatio = parseFloat(document.getElementById('newAspectRatio').value); var newWheelDiameter = parseFloat(document.getElementById('newWheelDiameter').value); var originalSpeed = parseFloat(document.getElementById('originalSpeed').value); var PI = Math.PI; var INCHES_PER_MM = 1 / 25.4; var INCHES_PER_MILE = 63360; // 1 mile = 63360 inches // Validate inputs if (isNaN(originalTireWidth) || isNaN(originalAspectRatio) || isNaN(originalWheelDiameter) || isNaN(newTireWidth) || isNaN(newAspectRatio) || isNaN(newWheelDiameter) || isNaN(originalSpeed) || originalTireWidth <= 0 || originalAspectRatio <= 0 || originalWheelDiameter <= 0 || newTireWidth <= 0 || newAspectRatio <= 0 || newWheelDiameter <= 0 || originalSpeed <= 0) { alert("Please enter valid positive numbers for all tire dimensions and speed."); return; } // Original Tire Calculations var originalSidewallHeightMM = (originalTireWidth * (originalAspectRatio / 100)); var originalSidewallHeightInches = originalSidewallHeightMM * INCHES_PER_MM; var originalOverallDiameter = originalWheelDiameter + (2 * originalSidewallHeightInches); var originalCircumference = originalOverallDiameter * PI; var originalRevsPerMile = INCHES_PER_MILE / originalCircumference; // New Tire Calculations var newSidewallHeightMM = (newTireWidth * (newAspectRatio / 100)); var newSidewallHeightInches = newSidewallHeightMM * INCHES_PER_MM; var newOverallDiameter = newWheelDiameter + (2 * newSidewallHeightInches); var newCircumference = newOverallDiameter * PI; var newRevsPerMile = INCHES_PER_MILE / newCircumference; // Comparison Calculations var diameterDifference = newOverallDiameter – originalOverallDiameter; var diameterDifferencePercent = (diameterDifference / originalOverallDiameter) * 100; var groundClearanceChange = diameterDifference / 2; var speedometerActualSpeed = originalSpeed * (newOverallDiameter / originalOverallDiameter); // Display Results document.getElementById('originalSidewall').innerText = originalSidewallHeightMM.toFixed(2); document.getElementById('originalDiameter').innerText = originalOverallDiameter.toFixed(2); document.getElementById('originalCircumference').innerText = originalCircumference.toFixed(2); document.getElementById('originalRevsPerMile').innerText = originalRevsPerMile.toFixed(2); document.getElementById('newSidewall').innerText = newSidewallHeightMM.toFixed(2); document.getElementById('newDiameter').innerText = newOverallDiameter.toFixed(2); document.getElementById('newCircumference').innerText = newCircumference.toFixed(2); document.getElementById('newRevsPerMile').innerText = newRevsPerMile.toFixed(2); document.getElementById('diameterDifference').innerText = diameterDifference.toFixed(2); document.getElementById('diameterDifferencePercent').innerText = diameterDifferencePercent.toFixed(2); document.getElementById('groundClearanceChange').innerText = groundClearanceChange.toFixed(2); document.getElementById('displayOriginalSpeed').innerText = originalSpeed.toFixed(0); document.getElementById('speedometerOriginal').innerText = originalSpeed.toFixed(0); document.getElementById('speedometerActual').innerText = speedometerActualSpeed.toFixed(2); }

Understanding Your Tire Size and Conversions

Changing your vehicle's tire size is a common modification, whether for aesthetic reasons, performance upgrades, or adapting to different driving conditions like off-roading. However, it's crucial to understand the implications of such changes, as they can affect everything from your speedometer accuracy to your vehicle's handling and fuel economy.

Decoding Tire Size Numbers

Tire sizes are typically displayed in a format like P205/55R16. Let's break down what each part means:

• P (or LT): This is the tire type. 'P' stands for Passenger car, 'LT' for Light Truck. If no letter is present, it's often a metric tire.
• 205: This is the Tire Width in millimeters (mm). It measures the tire from sidewall to sidewall.
• 55: This is the Aspect Ratio. It's the height of the tire's sidewall as a percentage of its width. In this case, the sidewall height is 55% of 205mm.
• R: Indicates radial construction, which is the most common type of tire today.
• 16: This is the Wheel Diameter (or rim diameter) in inches. It tells you what size wheel the tire is designed to fit.

Why Use a Tire Size Converter?

Our Tire Size Converter Calculator helps you compare your current tire specifications with a potential new size. This is vital for:

• Speedometer Accuracy: A common issue when changing tire diameter. If your new tires are larger, your speedometer will read slower than your actual speed, and vice-versa. This calculator shows you the exact difference.
• Ground Clearance: Larger tires increase ground clearance, which can be beneficial for off-roading. Smaller tires reduce it.
• Fender Clearance: Ensuring the new tires won't rub against your vehicle's fenders or suspension components, especially during turns or when the suspension compresses.
• Gearing and Performance: A significant change in tire diameter can alter your effective gear ratio, impacting acceleration, towing capacity, and fuel efficiency.
• Aesthetics: Many enthusiasts change tire sizes to achieve a specific look for their vehicle.

How the Calculator Works

The calculator takes your original and new tire dimensions (width, aspect ratio, and wheel diameter) and performs the following calculations:

1. Sidewall Height: Calculates the height of the tire's sidewall in millimeters. This is derived from the tire width and aspect ratio.
2. Overall Diameter: Determines the total height of the tire from the ground to the top, in inches. This is the sum of the wheel diameter plus twice the sidewall height.
3. Circumference: Calculates the distance covered by one full rotation of the tire, in inches.
4. Revolutions per Mile: Estimates how many times the tire rotates to cover one mile.
5. Diameter Difference: Shows the absolute and percentage difference between the original and new tire diameters.
6. Ground Clearance Change: Indicates how much your vehicle's ground clearance will increase or decrease.
7. Speedometer Reading: Crucially, it tells you what your actual speed will be if your speedometer is calibrated for the original tires and reads a certain speed (which you input).

Important Considerations Before Changing Tire Sizes

• Fender and Suspension Clearance: Always double-check that the new tires will fit without rubbing, especially when turning or under full suspension compression.
• Brake Clearance: Larger wheels might interfere with brake calipers, especially on vehicles with performance brake systems.
• Load Rating: Ensure the new tires have an adequate load rating for your vehicle's weight and intended use.
• TPMS (Tire Pressure Monitoring System): If your vehicle has TPMS, ensure the new wheels and tires are compatible.
• Insurance: Inform your insurance provider about significant modifications to avoid potential issues.

Use this calculator as a guide to make informed decisions about your tire choices, ensuring safety, performance, and compliance with your vehicle's specifications.