Tire Comparison Calculator

Tire Size Comparison Calculator

Use this calculator to compare two different tire sizes and understand how changing your tire dimensions can affect your vehicle's speedometer, overall diameter, and revolutions per mile.

Current Tire (Tire 1)

New/Comparison Tire (Tire 2)

Comparison Results:

function calculateTireComparison() { var tire1Width = parseFloat(document.getElementById('tire1Width').value); var tire1Aspect = parseFloat(document.getElementById('tire1Aspect').value); var tire1Rim = parseFloat(document.getElementById('tire1Rim').value); var tire2Width = parseFloat(document.getElementById('tire2Width').value); var tire2Aspect = parseFloat(document.getElementById('tire2Aspect').value); var tire2Rim = parseFloat(document.getElementById('tire2Rim').value); var resultDiv = document.getElementById('tireComparisonResult'); var tire1DetailsDiv = document.getElementById('tire1Details'); var tire2DetailsDiv = document.getElementById('tire2Details'); var speedometerDifferenceDiv = document.getElementById('speedometerDifference'); if (isNaN(tire1Width) || isNaN(tire1Aspect) || isNaN(tire1Rim) || isNaN(tire2Width) || isNaN(tire2Aspect) || isNaN(tire2Rim) || tire1Width <= 0 || tire1Aspect <= 0 || tire1Rim <= 0 || tire2Width <= 0 || tire2Aspect <= 0 || tire2Rim 0) { speedometerMessage = "If your speedometer reads 60 mph, your actual speed with the new tires would be approximately " + (60 * diameterRatio).toFixed(1) + " mph. (Speedometer will read " + Math.abs(speedDifferencePercent).toFixed(2) + "% too slow)"; } else if (speedDifferencePercent < 0) { speedometerMessage = "If your speedometer reads 60 mph, your actual speed with the new tires would be approximately " + (60 * diameterRatio).toFixed(1) + " mph. (Speedometer will read " + Math.abs(speedDifferencePercent).toFixed(2) + "% too fast)"; } else { speedometerMessage = "Your speedometer reading will be accurate with the new tires."; } tire1DetailsDiv.innerHTML = "

Tire 1 (Current):

" + "Sidewall Height: " + tire1SidewallHeight.toFixed(2) + " mm" + "Overall Diameter: " + tire1OverallDiameterMM.toFixed(2) + " mm (" + tire1OverallDiameterInches.toFixed(2) + " inches)" + "Circumference: " + tire1CircumferenceMM.toFixed(2) + " mm" + "Revolutions per Km: " + tire1RevsPerKm.toFixed(2) + "" + "Revolutions per Mile: " + tire1RevsPerMile.toFixed(2) + ""; tire2DetailsDiv.innerHTML = "

Tire 2 (New/Comparison):

" + "Sidewall Height: " + tire2SidewallHeight.toFixed(2) + " mm" + "Overall Diameter: " + tire2OverallDiameterMM.toFixed(2) + " mm (" + tire2OverallDiameterInches.toFixed(2) + " inches)" + "Circumference: " + tire2CircumferenceMM.toFixed(2) + " mm" + "Revolutions per Km: " + tire2RevsPerKm.toFixed(2) + "" + "Revolutions per Mile: " + tire2RevsPerMile.toFixed(2) + ""; speedometerDifferenceDiv.innerHTML = "

Speedometer Difference:

" + "Overall Diameter Difference: " + (tire2OverallDiameterInches – tire1OverallDiameterInches).toFixed(2) + " inches" + "Percentage Difference: " + speedDifferencePercent.toFixed(2) + "%" + "" + speedometerMessage + ""; }

Understanding Your Tire Size: A Comprehensive Guide

Choosing the right tires for your vehicle is crucial for safety, performance, and even fuel efficiency. While many drivers stick to the factory-recommended size, some opt for different dimensions for aesthetic reasons, performance upgrades, or to accommodate suspension modifications. Our Tire Size Comparison Calculator helps you understand the precise impact of changing your tire dimensions.

How Tire Sizes Are Measured

Tire sizes are typically expressed in a series of numbers and letters, like "205/55R16". Let's break down what each part means:

• Tire Width (e.g., 205): This is the width of the tire in millimeters, measured from sidewall to sidewall. A wider tire generally offers more grip but can also increase rolling resistance.
• Aspect Ratio (e.g., 55): This number represents the sidewall height as a percentage of the tire's width. In our example, the sidewall height is 55% of 205mm. A lower aspect ratio means a shorter sidewall, often found on performance tires, offering better handling but a harsher ride.
• Rim Diameter (e.g., 16): This is the diameter of the wheel (rim) in inches that the tire is designed to fit. Larger rim diameters often mean lower aspect ratio tires to maintain a similar overall tire diameter.

What the Calculator Compares

Our calculator takes your current tire size and a new/comparison tire size, then provides key metrics for both, along with a crucial comparison:

• Sidewall Height: The vertical distance from the wheel rim to the top of the tread. This directly impacts ride comfort and the tire's ability to absorb impacts.
• Overall Diameter: The total height of the tire from the ground to the top. This is a critical measurement as it affects gearing, speedometer accuracy, and fender clearance.
• Circumference: The distance covered by one full rotation of the tire.
• Revolutions per Kilometer/Mile: How many times the tire rotates to cover a kilometer or a mile. This is directly related to the overall diameter.
• Speedometer Difference: This is perhaps the most important output. If your new tires have a different overall diameter than your original tires, your vehicle's speedometer will no longer be accurate. The calculator shows you the percentage difference and what your actual speed would be if your speedometer reads a certain value (e.g., 60 mph).

Example Scenario: Upgrading Wheels

Let's say your car currently runs on 205/55R16 tires. You want to upgrade to 17-inch wheels and are considering 225/45R17 tires.

• Current Tire (205/55R16):
  • Width: 205 mm
  • Aspect Ratio: 55%
  • Rim Diameter: 16 inches
  • Calculated Overall Diameter: Approximately 631.9 mm (24.88 inches)
  • Revolutions per Mile: Approximately 809
• New Tire (225/45R17):
  • Width: 225 mm
  • Aspect Ratio: 45%
  • Rim Diameter: 17 inches
  • Calculated Overall Diameter: Approximately 634.3 mm (24.97 inches)
  • Revolutions per Mile: Approximately 806

In this example, the new tire is slightly larger in overall diameter (about 0.09 inches). This means if your speedometer reads 60 mph, your actual speed would be closer to 60.2 mph, and your speedometer would read approximately 0.38% too slow. This is a minor difference and generally acceptable.

Why Tire Comparison Matters

Changing tire sizes without understanding the implications can lead to several issues:

• Speedometer Error: As shown above, a different overall diameter will cause your speedometer to read inaccurately, potentially leading to speeding tickets or misjudging distances.
• Odometer Error: Your odometer will also be affected, leading to incorrect mileage readings, which can impact resale value and service intervals.
• Fender Clearance: Larger tires might rub against your vehicle's fenders or suspension components, especially during turns or over bumps.
• Ride Quality: A lower aspect ratio (shorter sidewall) generally results in a firmer ride, while a taller sidewall provides more cushioning.
• Handling Characteristics: Wider tires can improve grip, but a significant change in overall diameter can alter your vehicle's center of gravity and handling dynamics.
• Gearing and Performance: A larger overall diameter effectively "raises" your vehicle's gearing, potentially reducing acceleration but slightly improving highway fuel economy (if the engine can handle the taller gearing). Conversely, smaller tires "lower" gearing, improving acceleration but potentially increasing engine RPMs at highway speeds.
• ABS/Traction Control: Modern vehicles rely on precise wheel speed sensor readings. Significant changes in tire diameter can confuse these systems, potentially affecting their performance.

Always consult your vehicle's manufacturer recommendations and consider professional advice before making significant changes to your tire size.