Tire Plus Size Calculator
Original Tire Specifications
The first number in your tire size (e.g., 205 in 205/55R16).
The second number, representing sidewall height as a percentage of width (e.g., 55 in 205/55R16).
The last number, indicating the rim diameter (e.g., 16 in 205/55R16).
New Tire Specifications
The width of the new tire you are considering.
The aspect ratio of the new tire.
The rim diameter for the new tire.
Speedometer Input (Optional)
Enter a speed to see the speedometer error with the new tires.
Calculation Results
'; resultHtml += '';
resultHtml += '
';
resultHtml += 'Original Tire (' + originalWidth + '/' + originalAspect + 'R' + originalRim + ')
'; resultHtml += 'Sidewall Height: ' + originalSidewallHeight_mm.toFixed(2) + ' mm'; resultHtml += 'Overall Diameter: ' + originalOverallDiameter_mm.toFixed(2) + ' mm (' + originalOverallDiameter_inches.toFixed(2) + ' inches)'; resultHtml += 'Revolutions per Mile: ' + originalRevsPerMile.toFixed(2) + ''; resultHtml += '';
resultHtml += '
';
resultHtml += 'New Tire (' + newWidth + '/' + newAspect + 'R' + newRim + ')
'; resultHtml += 'Sidewall Height: ' + newSidewallHeight_mm.toFixed(2) + ' mm'; resultHtml += 'Overall Diameter: ' + newOverallDiameter_mm.toFixed(2) + ' mm (' + newOverallDiameter_inches.toFixed(2) + ' inches)'; resultHtml += 'Revolutions per Mile: ' + newRevsPerMile.toFixed(2) + ''; resultHtml += '';
resultHtml += '
';
if (!isNaN(speedometerSpeed) && speedometerSpeed > 0) {
resultHtml += 'Differences
'; resultHtml += 'Overall Diameter Difference: ' + diameterDiff_mm.toFixed(2) + ' mm (' + diameterDiff_percent.toFixed(2) + '%)'; resultHtml += 'Sidewall Height Difference: ' + sidewallDiff_mm.toFixed(2) + ' mm (' + sidewallDiff_percent.toFixed(2) + '%)'; resultHtml += 'Revolutions per Mile Difference: ' + revsDiff_count.toFixed(2) + ' (' + revsDiff_percent.toFixed(2) + '%)'; resultHtml += '';
resultHtml += '
';
}
if (Math.abs(diameterDiff_percent) > 3) {
resultHtml += 'Warning: The overall diameter difference is ' + diameterDiff_percent.toFixed(2) + '%. A difference greater than +/- 3% is generally not recommended and can cause issues with speedometer accuracy, ABS, traction control, and potential rubbing.';
} else {
resultHtml += 'The overall diameter difference is within the generally recommended +/- 3% range.';
}
document.getElementById('result').innerHTML = resultHtml;
}
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Speedometer Correction
'; resultHtml += 'If your speedometer reads ' + speedometerSpeed.toFixed(0) + ', your actual speed with the new tires will be approximately ' + actualSpeed.toFixed(1) + '.'; resultHtml += 'Speedometer Error: ' + speedometerError.toFixed(1) + ' (' + speedometerErrorPercent.toFixed(2) + '%)'; resultHtml += 'A positive error means your actual speed is higher than what the speedometer shows. A negative error means your actual speed is lower.'; resultHtml += 'Understanding Tire Plus Sizing and Why It Matters
Tire plus sizing is a common modification for vehicle owners looking to change the aesthetics or performance characteristics of their car. It involves changing the size of your tires and wheels while attempting to maintain the overall diameter of the wheel and tire assembly as close to the original as possible. This calculator helps you compare your current tire setup with a potential new one, providing crucial data to make an informed decision.
What is Plus Sizing?
Plus sizing typically means increasing the rim diameter (e.g., from 16 inches to 17 inches) while simultaneously decreasing the tire's aspect ratio (sidewall height) and often increasing the tire's width. The goal is to keep the total outside diameter of the tire relatively consistent with the factory specifications. For example, if you have a 205/55R16 tire, a common plus-one size might be 225/45R17.
How to Read Tire Sizes (e.g., 205/55R16)
- 205: This is the tire's width in millimeters, measured from sidewall to sidewall.
- 55: This is the aspect ratio, representing the sidewall height as a percentage of the tire's width. In this case, the sidewall height is 55% of 205mm.
- R: Indicates a radial construction tire.
- 16: This is the diameter of the wheel (rim) in inches that the tire is designed to fit.
Why Use a Tire Plus Size Calculator?
Changing tire sizes without proper calculation can lead to several issues. This calculator provides essential metrics to help you understand the impact of your tire choices:
- Speedometer Accuracy: If the new tire's overall diameter is significantly different from the original, your speedometer will read incorrectly. A larger diameter tire will make your speedometer read lower than your actual speed, while a smaller diameter tire will make it read higher.
- ABS and Traction Control: Modern vehicles rely on accurate wheel speed sensor readings for their Anti-lock Braking System (ABS) and Traction Control System (TCS). Significant changes in tire diameter can confuse these systems, potentially impairing their performance.
- Fender Clearance: Larger overall diameters or wider tires might rub against your vehicle's fenders, suspension components, or inner wheel wells, especially during turns or over bumps.
- Ride Quality and Handling: A lower aspect ratio (shorter sidewall) generally leads to a stiffer ride but can improve handling and steering response. A wider tire can increase grip but might also increase rolling resistance and road noise.
- Load Capacity: Ensure the new tires have an adequate load capacity rating for your vehicle.
Benefits of Plus Sizing
- Improved Aesthetics: Larger wheels and lower profile tires often give a vehicle a more aggressive or sporty look.
- Enhanced Handling: Shorter, stiffer sidewalls reduce tire flex, leading to better cornering stability and more precise steering response.
- Increased Grip: Wider tires can provide a larger contact patch with the road, potentially improving dry grip and braking performance.
Important Considerations
While plus sizing offers benefits, it's crucial to stay within acceptable limits. Most experts recommend keeping the overall diameter difference within +/- 3% of the original tire's diameter. Exceeding this range can lead to the issues mentioned above, including potential safety concerns and premature wear on suspension components.
Always consult your vehicle's manufacturer guidelines or a reputable tire professional before making significant changes to your tire and wheel setup.