Tire Size Comparison Calculator
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Tire Size Comparison Calculator
Compare two tire sizes to understand their differences in diameter, sidewall height, and speedometer accuracy.
Calculations are approximate. Tire pressure and load can affect actual dimensions.
Understanding Tire Size and Its Impact
Choosing the right tire size for your vehicle is crucial for performance, safety, and fuel efficiency. The tire size designation, such as P225/60R17, might seem cryptic, but it contains vital information about the tire's dimensions. This calculator helps you compare two different tire sizes by breaking down their physical attributes and predicting potential impacts on your speedometer and overall driving experience.
Decoding Tire Size Numbers
A standard tire size is typically presented in the format: [Service Description] [Width]/[Aspect Ratio] [Radial Construction] [Rim Diameter].
- Width (e.g., 225): This is the width of the tire in millimeters (mm) from sidewall to sidewall.
- Aspect Ratio (e.g., 60): This is the ratio of the tire's sidewall height to its width, expressed as a percentage. A 60 aspect ratio means the sidewall height is 60% of the tire's width (e.g., 0.60 * 225 mm).
- R: Indicates the tire has a Radial construction, which is standard for most modern vehicles.
- Rim Diameter (e.g., 17): This is the diameter of the wheel (rim) in inches that the tire is designed to fit.
How the Calculator Works
This calculator performs the following calculations to compare two tire sizes:
- Section Width (mm): Directly taken from the input.
- Sidewall Height (mm): Calculated as (Section Width * Aspect Ratio) / 100.
- Overall Tire Diameter (in): Calculated as (Sidewall Height * 2) + Rim Diameter. This represents the total height of the tire from the road surface to the top.
- Revolutions Per Mile: Calculated as (63360 / Overall Tire Diameter). This indicates how many times the tire rotates to cover one mile.
- Speedometer Error (%): The difference in revolutions per mile between the two tires is used to estimate potential speedometer error. A larger overall diameter will make the speedometer read slower than the actual speed, and vice-versa.
The calculator highlights the differences in diameter and estimates the percentage difference in revolutions per mile, which directly correlates to potential speedometer inaccuracy.
When to Use This Calculator
- Upgrading Wheels and Tires: If you're changing your rim size, you'll likely need to adjust the tire's aspect ratio and width to maintain a similar overall diameter. This calculator helps you find compatible sizes.
- Checking for Fitment Issues: Larger diameter tires might rub against fenders or suspension components. While this calculator doesn't measure clearance, understanding the diameter is a first step.
- Ensuring Speedometer Accuracy: Mismatched tire sizes can lead to inaccurate speedometer readings, affecting mileage tracking and speed enforcement.
- Optimizing Performance: Different tire sizes can impact handling, acceleration, and fuel economy. Comparing sizes helps you make informed decisions.
Important Considerations
Always consult your vehicle's owner's manual or a professional tire dealer before installing non-standard tire sizes. Ensure that any new tire size is compatible with your vehicle's braking system, suspension, and potentially its electronic stability control and anti-lock braking systems.
function compareTires() {
var width1 = parseFloat(document.getElementById("width1").value);
var aspectRatio1 = parseFloat(document.getElementById("aspectRatio1").value);
var rimDiameter1 = parseFloat(document.getElementById("rimDiameter1").value);
var width2 = parseFloat(document.getElementById("width2").value);
var aspectRatio2 = parseFloat(document.getElementById("aspectRatio2").value);
var rimDiameter2 = parseFloat(document.getElementById("rimDiameter2").value);
var resultDiv = document.getElementById("comparisonResult");
var detailsDiv = document.getElementById("comparisonDetails");
detailsDiv.innerHTML = ""; // Clear previous details
resultDiv.innerHTML = ""; // Clear previous result
if (isNaN(width1) || isNaN(aspectRatio1) || isNaN(rimDiameter1) ||
isNaN(width2) || isNaN(aspectRatio2) || isNaN(rimDiameter2) ||
width1 <= 0 || aspectRatio1 <= 0 || rimDiameter1 <= 0 ||
width2 <= 0 || aspectRatio2 <= 0 || rimDiameter2 <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
resultDiv.style.backgroundColor = "#ffc107"; // Yellow for warning
resultDiv.style.color = "#333";
return;
}
// Calculate dimensions for Tire 1
var sidewallHeight1 = (width1 * aspectRatio1) / 100; // in mm
var overallDiameter1 = (sidewallHeight1 * 2) / 25.4 + rimDiameter1; // Convert mm to inches and add rim diameter
var revolutionsPerMile1 = 63360 / overallDiameter1;
// Calculate dimensions for Tire 2
var sidewallHeight2 = (width2 * aspectRatio2) / 100; // in mm
var overallDiameter2 = (sidewallHeight2 * 2) / 25.4 + rimDiameter2; // Convert mm to inches and add rim diameter
var revolutionsPerMile2 = 63360 / overallDiameter2;
// Calculate differences
var diameterDifference = overallDiameter2 – overallDiameter1;
var diameterDifferencePercent = (diameterDifference / overallDiameter1) * 100;
var rpmDifferencePercent = ((revolutionsPerMile2 – revolutionsPerMile1) / revolutionsPerMile1) * 100;
var comparisonMessage = "";
var resultClass = "";
if (Math.abs(diameterDifferencePercent) 0) {
comparisonMessage = "Tire Size 2 is larger than Tire Size 1.";
resultClass = "negative"; // Red for larger diameter on second tire
} else {
comparisonMessage = "Tire Size 2 is smaller than Tire Size 1.";
resultClass = "positive"; // Green for smaller diameter on second tire
}
resultDiv.innerHTML = comparisonMessage;
resultDiv.className = "comparisonResult " + resultClass;
// Display detailed comparison
detailsDiv.innerHTML = `
Tire Size 1 Details:
Sidewall Height: ${sidewallHeight1.toFixed(2)} mm
Overall Diameter: ${overallDiameter1.toFixed(2)} inches
Revolutions Per Mile: ${revolutionsPerMile1.toFixed(2)}
Tire Size 2 Details:
Sidewall Height: ${sidewallHeight2.toFixed(2)} mm
Overall Diameter: ${overallDiameter2.toFixed(2)} inches
Revolutions Per Mile: ${revolutionsPerMile2.toFixed(2)}
Comparison Summary:
Diameter Difference: ${diameterDifference.toFixed(2)} inches (${diameterDifferencePercent.toFixed(2)}%)
Speedometer Accuracy (Estimated):
If Tire Size 2 is installed:
At 60 mph indicated, your actual speed is approximately ${ (60 * (1 + rpmDifferencePercent / 100)).toFixed(1) } mph.
Difference in RPM: ${rpmDifferencePercent.toFixed(2)}%
`;
}