Wheel Size Comparison Calculator
Use this calculator to compare the overall diameter, circumference, and revolutions per mile of two different wheel and tire setups. Understanding these differences is crucial for speedometer accuracy, fender clearance, and overall vehicle performance when changing tire sizes.
Wheel & Tire Setup 1
Wheel Diameter (inches):
Tire Width (mm):
Aspect Ratio (%):
Wheel & Tire Setup 2
Wheel Diameter (inches):
Tire Width (mm):
Aspect Ratio (%):
Compare Wheel Sizes
Understanding Tire Sizes
Tire sizes are typically expressed in a format like 225/45R17. Let's break down what each part means:
225: This is the Tire Width in millimeters (mm). It measures the width of the tire from sidewall to sidewall.45: 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 45% of 225mm.R: Indicates a radial construction tire, which is the most common type today.17: This is the Wheel Diameter in inches. It specifies the diameter of the wheel that the tire is designed to fit.
Why Compare Wheel Sizes?
Changing your vehicle's wheel and tire size can have several implications:
Speedometer Accuracy: If the overall diameter of your new tires is different from the original equipment, your speedometer and odometer will read inaccurately. A larger diameter tire will make your speedometer read lower than your actual speed, and a smaller diameter tire will make it read higher.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: Tires with a higher aspect ratio (taller sidewall) generally provide a more comfortable ride, while lower aspect ratio tires (shorter sidewall) can offer better handling and a sportier feel, but often at the expense of comfort.Gearing and Performance: A significant change in overall tire diameter can affect your vehicle's effective gear ratio, impacting acceleration, fuel economy, and even transmission shift points.Aesthetics: Many people change wheel and tire sizes for cosmetic reasons, to achieve a specific look for their vehicle.
This calculator helps you quickly assess the key dimensional differences between two setups, allowing you to make informed decisions before purchasing new wheels and tires.
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.wheel-size-comparison-calculator h2,
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@media (max-width: 600px) {
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function calculateWheelComparison() {
// Get input values for Wheel 1
var wheel1Diameter = parseFloat(document.getElementById("wheel1Diameter").value);
var wheel1Width = parseFloat(document.getElementById("wheel1Width").value);
var wheel1Aspect = parseFloat(document.getElementById("wheel1Aspect").value);
// Get input values for Wheel 2
var wheel2Diameter = parseFloat(document.getElementById("wheel2Diameter").value);
var wheel2Width = parseFloat(document.getElementById("wheel2Width").value);
var wheel2Aspect = parseFloat(document.getElementById("wheel2Aspect").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// Validate inputs
if (isNaN(wheel1Diameter) || isNaN(wheel1Width) || isNaN(wheel1Aspect) ||
isNaN(wheel2Diameter) || isNaN(wheel2Width) || isNaN(wheel2Aspect) ||
wheel1Diameter <= 0 || wheel1Width <= 0 || wheel1Aspect <= 0 ||
wheel2Diameter <= 0 || wheel2Width <= 0 || wheel2Aspect <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Constants
var MM_TO_INCH = 25.4;
var PI = Math.PI;
var FEET_PER_MILE = 5280;
// — Calculations for Wheel 1 —
var wheel1SidewallHeightMM = wheel1Width * (wheel1Aspect / 100);
var wheel1SidewallHeightInches = wheel1SidewallHeightMM / MM_TO_INCH;
var wheel1OverallDiameterInches = wheel1Diameter + (2 * wheel1SidewallHeightInches);
var wheel1CircumferenceInches = wheel1OverallDiameterInches * PI;
var wheel1CircumferenceFeet = wheel1CircumferenceInches / 12;
var wheel1RevolutionsPerMile = FEET_PER_MILE / wheel1CircumferenceFeet;
// — Calculations for Wheel 2 —
var wheel2SidewallHeightMM = wheel2Width * (wheel2Aspect / 100);
var wheel2SidewallHeightInches = wheel2SidewallHeightMM / MM_TO_INCH;
var wheel2OverallDiameterInches = wheel2Diameter + (2 * wheel2SidewallHeightInches);
var wheel2CircumferenceInches = wheel2OverallDiameterInches * PI;
var wheel2CircumferenceFeet = wheel2CircumferenceInches / 12;
var wheel2RevolutionsPerMile = FEET_PER_MILE / wheel2CircumferenceFeet;
// — Comparison Results —
var diameterDifference = wheel2OverallDiameterInches – wheel1OverallDiameterInches;
var circumferenceDifference = wheel2CircumferenceInches – wheel1CircumferenceInches;
var revsPerMileDifference = wheel2RevolutionsPerMile – wheel1RevolutionsPerMile;
// Speedometer Error Calculation (assuming original is Wheel 1, new is Wheel 2)
var speedometerErrorPercentage = ((wheel2OverallDiameterInches – wheel1OverallDiameterInches) / wheel1OverallDiameterInches) * 100;
var speedometerReads60 = 60; // mph
var actualSpeedAt60 = speedometerReads60 * (wheel2OverallDiameterInches / wheel1OverallDiameterInches);
var speedDifferenceAt60 = actualSpeedAt60 – speedometerReads60;
// Display Results
var resultsHTML = "
Comparison Results ";
resultsHTML += "
Setup 1 Overall Diameter: " + wheel1OverallDiameterInches.toFixed(2) + " inches ";
resultsHTML += "
Setup 1 Circumference: " + wheel1CircumferenceInches.toFixed(2) + " inches ";
resultsHTML += "
Setup 1 Revolutions per Mile: " + wheel1RevolutionsPerMile.toFixed(0) + " revs ";
resultsHTML += "
";
resultsHTML += "
Setup 2 Overall Diameter: " + wheel2OverallDiameterInches.toFixed(2) + " inches ";
resultsHTML += "
Setup 2 Circumference: " + wheel2CircumferenceInches.toFixed(2) + " inches ";
resultsHTML += "
Setup 2 Revolutions per Mile: " + wheel2RevolutionsPerMile.toFixed(0) + " revs ";
resultsHTML += "
";
resultsHTML += "
Overall Diameter Difference: " + (diameterDifference > 0 ? "+" : "") + diameterDifference.toFixed(2) + " inches ";
resultsHTML += "
Circumference Difference: " + (circumferenceDifference > 0 ? "+" : "") + circumferenceDifference.toFixed(2) + " inches ";
resultsHTML += "
Revolutions per Mile Difference: " + (revsPerMileDifference > 0 ? "+" : "") + revsPerMileDifference.toFixed(0) + " revs ";
resultsHTML += "
";
resultsHTML += "
Speedometer Error: " + speedometerErrorPercentage.toFixed(2) + "% ";
if (speedometerErrorPercentage > 0) {
resultsHTML += "
If speedometer reads 60 mph: Actual speed is " + actualSpeedAt60.toFixed(2) + " mph (+" + speedDifferenceAt60.toFixed(2) + " mph) ";
} else if (speedometerErrorPercentage < 0) {
resultsHTML += "
If speedometer reads 60 mph: Actual speed is " + actualSpeedAt60.toFixed(2) + " mph (" + speedDifferenceAt60.toFixed(2) + " mph) ";
} else {
resultsHTML += "
If speedometer reads 60 mph: Actual speed is 60.00 mph (No difference) ";
}
resultDiv.innerHTML = resultsHTML;
}