Discount Tire Size Calculator

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Tire Size Comparison Calculator

Original Tire Size

New Tire Size

Comparison Results

Original Tire Specs

Sidewall Height: inches

Overall Diameter: inches

Overall Circumference: inches

Revolutions Per Mile:

New Tire Specs

Sidewall Height: inches

Overall Diameter: inches

Overall Circumference: inches

Revolutions Per Mile:

Differences & Impact

Overall Diameter Difference:

Sidewall Height Difference: inches

Circumference Difference: inches

Revolutions Per Mile Difference:

Speedometer Impact:

function calculateTireSizes() { var originalWidth = parseFloat(document.getElementById('originalWidth').value); var originalAspect = parseFloat(document.getElementById('originalAspect').value); var originalWheel = parseFloat(document.getElementById('originalWheel').value); var newWidth = parseFloat(document.getElementById('newWidth').value); var newAspect = parseFloat(document.getElementById('newAspect').value); var newWheel = parseFloat(document.getElementById('newWheel').value); // Input validation if (isNaN(originalWidth) || isNaN(originalAspect) || isNaN(originalWheel) || isNaN(newWidth) || isNaN(newAspect) || isNaN(newWheel) || originalWidth <= 0 || originalAspect <= 0 || originalWheel <= 0 || newWidth <= 0 || newAspect <= 0 || newWheel 0.5) { // New tire is significantly larger speedometerImpactText = 'When your speedometer reads 60 MPH, your actual speed will be ' + (60 * (newDiameter / originalDiameter)).toFixed(1) + ' MPH. (New tire is larger)'; } else if (diameterDiffPercent < -0.5) { // New tire is significantly smaller speedometerImpactText = 'When your speedometer reads 60 MPH, your actual speed will be ' + (60 * (newDiameter / originalDiameter)).toFixed(1) + ' MPH. (New tire is smaller)'; } else { speedometerImpactText = 'Minimal speedometer impact (less than 0.5% difference).'; } // — Display Results — document.getElementById('originalSidewall').innerHTML = originalSidewall.toFixed(2); document.getElementById('originalDiameter').innerHTML = originalDiameter.toFixed(2); document.getElementById('originalCircumference').innerHTML = originalCircumference.toFixed(2); document.getElementById('originalRevs').innerHTML = originalRevsPerMile.toFixed(0); document.getElementById('newSidewall').innerHTML = newSidewall.toFixed(2); document.getElementById('newDiameter').innerHTML = newDiameter.toFixed(2); document.getElementById('newCircumference').innerHTML = newCircumference.toFixed(2); document.getElementById('newRevs').innerHTML = newRevsPerMile.toFixed(0); document.getElementById('diameterDiffPercent').innerHTML = diameterDiffPercent.toFixed(2) + '%'; document.getElementById('sidewallDiff').innerHTML = sidewallDiff.toFixed(2); document.getElementById('circumferenceDiff').innerHTML = circumferenceDiff.toFixed(2); document.getElementById('revsDiff').innerHTML = revsDiff.toFixed(0); document.getElementById('speedometerImpact').innerHTML = speedometerImpactText; document.getElementById('result').style.display = 'block'; }

Understanding Your Tire Size: A Comprehensive Guide

Choosing the right tires for your vehicle is crucial for safety, performance, and even fuel efficiency. Whether you're replacing worn-out tires, upgrading your wheels, or looking for a specific type of tire (like all-season, winter, or performance), understanding tire sizes is the first step. Our Tire Size Comparison Calculator helps you compare your current tire specifications with a potential new size, giving you insights into how the change will affect your vehicle.

Decoding Tire Size Numbers (e.g., 205/55R16)

Every tire has a series of numbers and letters molded into its sidewall. Let's break down what they mean:

  • 205 (Tire Width): This is the width of the tire in millimeters, measured from sidewall to sidewall. A wider tire generally offers more grip but can affect steering feel and fuel economy.
  • 55 (Aspect Ratio): This number represents the height of the tire's sidewall as a percentage of its width. In this example, the sidewall height is 55% of 205mm. A lower aspect ratio means a shorter sidewall, often found on performance tires for better handling, but potentially a harsher ride.
  • R (Construction Type): This indicates the tire's internal construction. 'R' stands for Radial, which is the most common type today.
  • 16 (Wheel Diameter): This is the diameter of the wheel (or rim) in inches that the tire is designed to fit.

How Tire Size Changes Affect Your Vehicle

Even small changes in tire size can have significant impacts:

  • Speedometer Accuracy: If your new tires have a different overall diameter than your original ones, your speedometer will no longer read accurately. A larger diameter tire will make your speedometer read slower than your actual speed, while a smaller diameter tire will make it read faster. Our calculator provides an estimate of this impact.
  • Ground Clearance: A larger overall diameter will increase your vehicle's ground clearance, which can be beneficial for off-roading but might raise your center of gravity.
  • Fender Clearance: Taller or wider tires might rub against your vehicle's fenders or suspension components, especially during turns or over bumps. Always check for adequate clearance.
  • Ride Quality: Tires with a lower aspect ratio (shorter sidewall) generally offer a firmer, sportier ride but can transmit more road imperfections. Taller sidewalls typically provide a more comfortable ride.
  • Handling and Performance: Wider tires can improve grip and cornering stability, but might also increase steering effort and hydroplaning risk in wet conditions.
  • Fuel Economy: Larger or wider tires can increase rolling resistance and weight, potentially leading to a slight decrease in fuel efficiency.
  • Braking Performance: Changes in tire size can subtly affect braking distances and ABS calibration.

Using the Tire Size Comparison Calculator

Our calculator simplifies the process of understanding these changes:

  1. Enter Original Tire Details: Input the width, aspect ratio, and wheel diameter of your current tires.
  2. Enter New Tire Details: Input the specifications of the tire size you are considering.
  3. Calculate: Click the "Calculate Tire Differences" button.

The calculator will instantly display the sidewall height, overall diameter, circumference, and revolutions per mile for both tire sizes. More importantly, it will show you the percentage difference in overall diameter and the direct impact on your speedometer, helping you make an informed decision.

When to Use This Calculator

  • Upgrading Wheels: If you're moving to larger or smaller diameter wheels.
  • Performance Tuning: When selecting tires for improved handling or aesthetics.
  • Replacing Worn Tires: To ensure your replacement tires are the correct size or to explore alternative compatible sizes.
  • Finding Discount Tires: When searching for the best deals on tires, this tool helps you verify if a discounted size is a suitable replacement for your vehicle.

Always consult your vehicle's owner's manual or a professional tire technician before making significant changes to your tire size to ensure compatibility and safety.

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