Tire Rim Calculator

Tire & Rim Size Calculator

function calculateTireRim() { var originalTireWidth = parseFloat(document.getElementById('originalTireWidth').value); var originalAspectRatio = parseFloat(document.getElementById('originalAspectRatio').value); var originalRimDiameter = parseFloat(document.getElementById('originalRimDiameter').value); var newTireWidth = parseFloat(document.getElementById('newTireWidth').value); var newAspectRatio = parseFloat(document.getElementById('newAspectRatio').value); var newRimDiameter = parseFloat(document.getElementById('newRimDiameter').value); // Input validation if (isNaN(originalTireWidth) || originalTireWidth <= 0 || isNaN(originalAspectRatio) || originalAspectRatio <= 0 || isNaN(originalRimDiameter) || originalRimDiameter <= 0 || isNaN(newTireWidth) || newTireWidth <= 0 || isNaN(newAspectRatio) || newAspectRatio <= 0 || isNaN(newRimDiameter) || newRimDiameter <= 0) { document.getElementById('result').innerHTML = '

Please enter valid positive numbers for all fields.

'; return; } var INCH_TO_MM = 25.4; // Original Tire Calculations var originalSidewallHeightMM = originalTireWidth * (originalAspectRatio / 100); var originalRimDiameterMM = originalRimDiameter * INCH_TO_MM; var originalOverallDiameterMM = (2 * originalSidewallHeightMM) + originalRimDiameterMM; var originalOverallDiameterInches = originalOverallDiameterMM / INCH_TO_MM; // New Tire Calculations var newSidewallHeightMM = newTireWidth * (newAspectRatio / 100); var newRimDiameterMM = newRimDiameter * INCH_TO_MM; var newOverallDiameterMM = (2 * newSidewallHeightMM) + newRimDiameterMM; var newOverallDiameterInches = newOverallDiameterMM / INCH_TO_MM; // Differences var diameterDifferenceInches = newOverallDiameterInches – originalOverallDiameterInches; var diameterDifferencePercent = (diameterDifferenceInches / originalOverallDiameterInches) * 100; var sidewallDifferenceMM = newSidewallHeightMM – originalSidewallHeightMM; var sidewallDifferencePercent = (sidewallDifferenceMM / originalSidewallHeightMM) * 100; // Speedometer Error (assuming original speed is 60 MPH/KPH) // If new tire is larger, actual speed is higher than indicated. // If new tire is smaller, actual speed is lower than indicated. var indicatedSpeed = 60; // Example speed var actualSpeed = indicatedSpeed * (newOverallDiameterInches / originalOverallDiameterInches); var speedometerErrorValue = actualSpeed – indicatedSpeed; var speedometerErrorPercent = (speedometerErrorValue / indicatedSpeed) * 100; // Display Results document.getElementById('originalOverallDiameter').innerHTML = 'Original Overall Diameter: ' + originalOverallDiameterInches.toFixed(2) + ' inches (' + originalOverallDiameterMM.toFixed(2) + ' mm)'; document.getElementById('newOverallDiameter').innerHTML = 'New Overall Diameter: ' + newOverallDiameterInches.toFixed(2) + ' inches (' + newOverallDiameterMM.toFixed(2) + ' mm)'; document.getElementById('diameterDifference').innerHTML = 'Diameter Difference: ' + diameterDifferenceInches.toFixed(2) + ' inches (' + diameterDifferencePercent.toFixed(2) + '%)'; document.getElementById('originalSidewallHeight').innerHTML = 'Original Sidewall Height: ' + originalSidewallHeightMM.toFixed(2) + ' mm'; document.getElementById('newSidewallHeight').innerHTML = 'New Sidewall Height: ' + newSidewallHeightMM.toFixed(2) + ' mm'; document.getElementById('sidewallDifference').innerHTML = 'Sidewall Height Difference: ' + sidewallDifferenceMM.toFixed(2) + ' mm (' + sidewallDifferencePercent.toFixed(2) + '%)'; var speedometerErrorText = "; if (speedometerErrorValue > 0) { speedometerErrorText = 'Your speedometer will read ' + indicatedSpeed + ' MPH, but your actual speed will be ' + actualSpeed.toFixed(2) + ' MPH (+' + speedometerErrorValue.toFixed(2) + ' MPH / +' + speedometerErrorPercent.toFixed(2) + '%)'; } else if (speedometerErrorValue < 0) { speedometerErrorText = 'Your speedometer will read ' + indicatedSpeed + ' MPH, but your actual speed will be ' + actualSpeed.toFixed(2) + ' MPH (' + speedometerErrorValue.toFixed(2) + ' MPH / ' + speedometerErrorPercent.toFixed(2) + '%)'; } else { speedometerErrorText = 'Your speedometer will be accurate at ' + indicatedSpeed + ' MPH.'; } document.getElementById('speedometerError').innerHTML = 'Speedometer Error (at ' + indicatedSpeed + ' MPH): ' + speedometerErrorText; document.getElementById('result').style.backgroundColor = '#e9f7ef'; document.getElementById('result').style.borderColor = '#d4edda'; document.getElementById('result').style.color = '#155724'; }

Understanding Your Tire & Rim Size Changes

Changing the tires or rims on your vehicle can significantly impact its performance, appearance, and even safety. Our Tire & Rim Size Calculator helps you understand the precise differences between your original setup and a new one, focusing on critical dimensions like overall diameter and sidewall height, and how these changes affect your speedometer.

Why Use a Tire & Rim Size Calculator?

When you upgrade or replace your wheels and tires, it's not just about aesthetics. The dimensions of your new setup can have several important consequences:

• Speedometer Accuracy: A change in the overall diameter of your wheel (tire + rim) will directly affect your speedometer reading. If the new wheel is larger, your speedometer will read slower than your actual speed. If it's smaller, it will read faster. This can lead to unintended speeding tickets or inaccurate navigation.
• Fender Clearance: Larger overall diameters or wider tires might rub against your vehicle's fenders or suspension components, especially during turns or over bumps.
• Ride Quality & Handling: Changes in sidewall height can alter your vehicle's ride comfort and handling characteristics. A lower aspect ratio (shorter sidewall) generally means a firmer ride and potentially sharper handling, while a taller sidewall offers more cushioning.
• Brake Clearance: Larger rims might be necessary to clear bigger brake calipers, especially in performance upgrades.
• Gear Ratio & Fuel Economy: A significant change in overall diameter can subtly alter your effective gear ratio, impacting acceleration and fuel efficiency.

How to Read Tire Sizes (e.g., 205/55R16)

Understanding your tire's specifications is crucial for using this calculator:

• 205 (Tire Width in mm): This is the width of the tire in millimeters, measured from sidewall to sidewall.
• 55 (Aspect Ratio %): This number represents the tire's sidewall height as a percentage of its width. In this example, the sidewall height is 55% of 205mm. A lower aspect ratio means a shorter sidewall.
• R (Construction Type): Indicates radial construction, which is standard for most modern passenger vehicle tires.
• 16 (Rim Diameter in inches): This is the diameter of the wheel rim in inches that the tire is designed to fit.

How the Calculator Works

The calculator takes your original and new tire specifications to determine:

1. Sidewall Height: Calculated by multiplying the tire width by the aspect ratio percentage.
2. Overall Diameter: This is the total height of the wheel, from the ground to the top of the tire. It's calculated by adding twice the sidewall height to the rim diameter (converted to the same unit).
3. Diameter Difference: The absolute and percentage difference between the original and new overall diameters.
4. Speedometer Error: By comparing the overall diameters, the calculator estimates how much your speedometer will be off at a given speed (e.g., 60 MPH). If your new tires are larger, your actual speed will be higher than what your speedometer indicates. If they are smaller, your actual speed will be lower.

Example Calculation

Let's say your original tires are 205/55R16 and you're considering new tires that are 225/45R17:

• Original Tire (205/55R16):
  • Tire Width: 205 mm
  • Aspect Ratio: 55%
  • Rim Diameter: 16 inches
  • Calculated Sidewall Height: 112.75 mm
  • Calculated Overall Diameter: 24.88 inches (631.9 mm)
• New Tire (225/45R17):
  • Tire Width: 225 mm
  • Aspect Ratio: 45%
  • Rim Diameter: 17 inches
  • Calculated Sidewall Height: 101.25 mm
  • Calculated Overall Diameter: 24.97 inches (634.3 mm)

In this example, the new setup results in a slightly larger overall diameter (approx. +0.09 inches or +0.38%) and a shorter sidewall (approx. -11.5 mm or -10.20%). This means if your speedometer reads 60 MPH, your actual speed would be approximately 60.23 MPH. This small difference might be acceptable, but larger changes could require speedometer recalibration.

Always consult with a professional tire specialist before making significant changes to your vehicle's tire and rim setup to ensure compatibility and safety.