Tire Size Comparison Calculator
Original Tire Size
Tire Width (mm):
Aspect Ratio (%):
Wheel Diameter (inches):
New Tire Size
Tire Width (mm):
Aspect Ratio (%):
Wheel Diameter (inches):
Comparison Results:
Please enter valid positive numbers for all tire dimensions.
'; return; } // Calculate original tire specs var originalSidewallHeight = originalWidth * (originalAspect / 100); // mm var originalWheelDiameterMM = originalWheel * 25.4; // inches to mm var originalOverallDiameter = originalWheelDiameterMM + (2 * originalSidewallHeight); // mm var originalOverallCircumference = originalOverallDiameter * Math.PI; // mm // Calculate new tire specs var newSidewallHeight = newWidth * (newAspect / 100); // mm var newWheelDiameterMM = newWheel * 25.4; // inches to mm var newOverallDiameter = newWheelDiameterMM + (2 * newSidewallHeight); // mm var newOverallCircumference = newOverallDiameter * Math.PI; // mm // Calculate differences var diameterDiffPercent = ((newOverallDiameter – originalOverallDiameter) / originalOverallDiameter) * 100; var circumferenceDiffPercent = ((newOverallCircumference – originalOverallCircumference) / originalOverallCircumference) * 100; var speedometerError = circumferenceDiffPercent; // Speedometer error is directly related to circumference change var rideHeightChange = (newOverallDiameter – originalOverallDiameter) / 2; // mm // Display results document.getElementById('originalTireSpecs').innerHTML = 'Original Tire: Sidewall Height: ' + originalSidewallHeight.toFixed(2) + ' mm, Overall Diameter: ' + originalOverallDiameter.toFixed(2) + ' mm, Overall Circumference: ' + originalOverallCircumference.toFixed(2) + ' mm.'; document.getElementById('newTireSpecs').innerHTML = 'New Tire: Sidewall Height: ' + newSidewallHeight.toFixed(2) + ' mm, Overall Diameter: ' + newOverallDiameter.toFixed(2) + ' mm, Overall Circumference: ' + newOverallCircumference.toFixed(2) + ' mm.'; document.getElementById('diameterDifference').innerHTML = 'Overall Diameter Difference: ' + diameterDiffPercent.toFixed(2) + '%'; document.getElementById('circumferenceDifference').innerHTML = 'Overall Circumference Difference: ' + circumferenceDiffPercent.toFixed(2) + '%'; document.getElementById('speedometerError').innerHTML = 'Speedometer Error: When your speedometer reads 60 mph, your actual speed will be approximately ' + (60 * (1 + (speedometerError / 100))).toFixed(2) + ' mph. (Error: ' + speedometerError.toFixed(2) + '%)'; document.getElementById('rideHeightChange').innerHTML = 'Ride Height Change: ' + rideHeightChange.toFixed(2) + ' mm (approx. ' + (rideHeightChange / 25.4).toFixed(2) + ' inches)'; }Understanding Your Tire Size and Its Impact
Changing tire sizes, whether for aesthetic reasons, performance upgrades, or simply finding a better deal, can have significant implications for your vehicle's performance, safety, and even its speedometer accuracy. Our Tire Size Comparison Calculator helps you understand these changes before you make a purchase.
Decoding Tire Size Numbers
A typical tire size, like 205/55R16, contains three crucial pieces of information:
- 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 fuel economy and steering feel.
- 55 (Aspect Ratio): This number represents the sidewall height as a percentage of the tire's 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.
- 16 (Wheel Diameter): This is the diameter of the wheel (or rim) in inches that the tire is designed to fit. Larger wheels often accommodate larger brakes and can enhance appearance, but may require lower aspect ratio tires to maintain overall diameter.
Why Compare Tire Sizes?
People often consider changing tire sizes for several reasons:
- Performance: Wider tires or lower aspect ratios can improve handling and cornering.
- Aesthetics: Larger wheels and different tire profiles can change the look of your vehicle.
- Cost/Availability: Sometimes a slightly different size might be more readily available or more affordable.
- Ride Comfort: Taller sidewalls (higher aspect ratio) generally provide a more comfortable ride.
- Off-roading: Larger overall diameter tires can increase ground clearance.
The Impact of Changing Tire Dimensions
Even small changes in tire dimensions can have noticeable effects:
- Speedometer Error: This is one of the most critical impacts. If your new tires have a different overall diameter than your original ones, your speedometer will no longer be accurate. If the new tires are larger, your speedometer will read slower than your actual speed. If they are smaller, it will read faster. This calculator provides the exact percentage of error.
- Ride Height: A change in overall tire diameter directly affects your vehicle's ride height. A larger diameter will lift your vehicle, while a smaller one will lower it.
- Fender Clearance: Larger or wider tires might rub against your vehicle's fenders or suspension components, especially during turns or over bumps.
- Handling and Braking: Changes in tire width, aspect ratio, and overall diameter can alter your vehicle's handling characteristics, steering response, and even braking performance.
- Fuel Economy: Larger or wider tires can increase rolling resistance, potentially leading to a slight decrease in fuel efficiency.
- Gear Ratios: A significant change in overall tire diameter can effectively alter your vehicle's final drive ratio, impacting acceleration and engine RPM at cruising speeds.
How to Use This Calculator
Simply input the width, aspect ratio, and wheel diameter for your current (original) tires and the new tires you are considering. The calculator will instantly provide you with:
- The calculated sidewall height, overall diameter, and circumference for both tire sets.
- The percentage difference in overall diameter and circumference between the two sizes.
- The estimated speedometer error, showing your actual speed when your speedometer reads 60 mph.
- The change in your vehicle's ride height.
Always consult with a professional tire installer or your vehicle manufacturer's specifications when considering significant tire size changes to ensure safety and compatibility.