Tire Size Comparison Calculator

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Tire Size Comparison Calculator

Current Tire Size

New Tire Size

Comparison Results

Current Tire Details:

Overall Diameter: 0.00 inches

Sidewall Height: 0.00 inches

Circumference: 0.00 inches

Revolutions Per Mile: 0

New Tire Details:

Overall Diameter: 0.00 inches

Sidewall Height: 0.00 inches

Circumference: 0.00 inches

Revolutions Per Mile: 0

Key Differences:

Overall Diameter Difference: 0.00 inches

Speedometer Difference: 0.00 %

Ground Clearance Change: 0.00 inches

A positive speedometer difference means your speedometer will read slower than actual speed. A negative difference means it will read faster.

function calculateTireComparison() { var currentTireWidth = parseFloat(document.getElementById("currentTireWidth").value); var currentAspectRatio = parseFloat(document.getElementById("currentAspectRatio").value); var currentRimDiameter = parseFloat(document.getElementById("currentRimDiameter").value); var newTireWidth = parseFloat(document.getElementById("newTireWidth").value); var newAspectRatio = parseFloat(document.getElementById("newAspectRatio").value); var newRimDiameter = parseFloat(document.getElementById("newRimDiameter").value); // Validate inputs if (isNaN(currentTireWidth) || isNaN(currentAspectRatio) || isNaN(currentRimDiameter) || isNaN(newTireWidth) || isNaN(newAspectRatio) || isNaN(newRimDiameter) || currentTireWidth <= 0 || currentAspectRatio <= 0 || currentRimDiameter <= 0 || newTireWidth <= 0 || newAspectRatio <= 0 || newRimDiameter <= 0) { alert("Please enter valid positive numbers for all tire dimensions."); return; } // — Current Tire Calculations — var currentSidewallHeightMM = currentTireWidth * (currentAspectRatio / 100); var currentSidewallHeightInches = currentSidewallHeightMM / 25.4; var currentOverallDiameter = (currentSidewallHeightInches * 2) + currentRimDiameter; var currentCircumference = currentOverallDiameter * Math.PI; var currentRevsPerMile = 63360 / currentCircumference; // 63360 inches in a mile // — New Tire Calculations — var newSidewallHeightMM = newTireWidth * (newAspectRatio / 100); var newSidewallHeightInches = newSidewallHeightMM / 25.4; var newOverallDiameter = (newSidewallHeightInches * 2) + newRimDiameter; var newCircumference = newOverallDiameter * Math.PI; var newRevsPerMile = 63360 / newCircumference; // — Comparison Calculations — var diameterDifference = newOverallDiameter – currentOverallDiameter; var speedometerDifference = ((newOverallDiameter – currentOverallDiameter) / currentOverallDiameter) * 100; var groundClearanceChange = diameterDifference / 2; // — Display Results — document.getElementById("currentOverallDiameter").innerText = currentOverallDiameter.toFixed(2); document.getElementById("currentSidewallHeight").innerText = currentSidewallHeightInches.toFixed(2); document.getElementById("currentCircumference").innerText = currentCircumference.toFixed(2); document.getElementById("currentRevsPerMile").innerText = Math.round(currentRevsPerMile); document.getElementById("newOverallDiameter").innerText = newOverallDiameter.toFixed(2); document.getElementById("newSidewallHeight").innerText = newSidewallHeightInches.toFixed(2); document.getElementById("newCircumference").innerText = newCircumference.toFixed(2); document.getElementById("newRevsPerMile").innerText = Math.round(newRevsPerMile); document.getElementById("diameterDifference").innerText = diameterDifference.toFixed(2); document.getElementById("speedometerDifference").innerText = speedometerDifference.toFixed(2); document.getElementById("groundClearanceChange").innerText = groundClearanceChange.toFixed(2); } // Run calculation on page load with default values window.onload = calculateTireComparison;

Understanding Tire Sizes and Their Impact

Changing your vehicle's tire size might seem like a simple modification, but it can have significant effects on performance, safety, and even your vehicle's onboard systems. Our Tire Size Comparison Calculator helps you understand these impacts by comparing your current tire specifications with a potential new size.

Decoding Tire Size Numbers

Tire sizes are typically displayed in a format like 205/55R16. Let's break down what each part means:

  • 205: This is the Tire Width in millimeters. It measures the tire from sidewall to sidewall.
  • 55: This is the Aspect Ratio, expressed as a percentage. It represents the sidewall height as a percentage of the tire's width. In this example, the sidewall height is 55% of 205mm.
  • R: This indicates the tire's construction type, with 'R' standing for Radial, the most common type.
  • 16: This is the Rim Diameter in inches, indicating the size of the wheel the tire is designed to fit.

Why Compare Tire Sizes?

When considering a change in tire size, whether for aesthetic reasons, performance upgrades, or simply replacing worn tires, it's crucial to understand the implications. Our calculator provides key metrics to help you make an informed decision:

Overall Diameter

The overall diameter is the total height of the tire when mounted and inflated. This is perhaps the most critical measurement. A change in overall diameter directly affects:

  • Speedometer Accuracy: If the new tire's diameter is different from the original, your speedometer will read incorrectly. A larger diameter tire will make your speedometer read slower than your actual speed, while a smaller diameter tire will make it read faster. This can lead to speeding tickets or misjudging distances.
  • Gearing: A larger diameter tire effectively changes your vehicle's final drive ratio, making it feel like you have "taller" gears. This can reduce acceleration but potentially improve fuel economy at highway speeds. Conversely, smaller tires make gears "shorter," improving acceleration but increasing engine RPM at speed.
  • Ground Clearance: Half of the change in overall diameter translates directly to a change in ground clearance. Larger tires lift the vehicle, while smaller tires lower it.
  • Fender Clearance: Larger tires might rub against your vehicle's fenders or suspension components, especially during turns or when the suspension compresses.

Sidewall Height

The sidewall height impacts the tire's profile and ride quality. A lower aspect ratio (smaller sidewall) typically means a stiffer ride and improved handling due to less sidewall flex, often seen in performance tires. A higher aspect ratio (taller sidewall) generally provides a more comfortable ride and better protection against potholes.

Circumference and Revolutions Per Mile

These metrics are directly related to the overall diameter. The circumference is the distance the tire travels in one full rotation. The revolutions per mile tell you how many times the tire spins to cover one mile. These are fundamental to speedometer calibration and understanding the effective gearing changes.

Using the Calculator

Simply input the width, aspect ratio, and rim diameter for your current tires and the new tires you are considering. The calculator will instantly provide detailed measurements for both tires and highlight the key differences, including:

  • Overall Diameter Difference: How much taller or shorter the new tire is.
  • Speedometer Difference (%): The percentage by which your speedometer will be off. A positive percentage means your speedometer will read slower than your actual speed (e.g., if it says 60 MPH, you're actually going 61.2 MPH for a +2% difference). A negative percentage means it will read faster.
  • Ground Clearance Change: How much your vehicle's ground clearance will increase or decrease.

Important Considerations

  • Manufacturer Recommendations: Always check your vehicle's owner's manual or the sticker on the driver's side door jamb for recommended tire sizes. Deviating too far can void warranties or affect safety systems.
  • Load Index and Speed Rating: Ensure any new tire meets or exceeds the load index and speed rating requirements for your vehicle.
  • TPMS (Tire Pressure Monitoring System): Significant changes in tire diameter can sometimes affect TPMS calibration.
  • ABS/Traction Control: Modern vehicles rely on precise wheel speed sensor readings. Large changes in tire diameter can confuse these systems, potentially impacting their performance.

By using this calculator, you can gain a clear understanding of how a tire size change will impact your vehicle, helping you make the best choice for your driving needs.

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