Tire and Wheel Fitment Calculator
Ensure your new tires and wheels will fit your vehicle perfectly. Enter your current tire size and the desired new tire size.
Fitment Comparison
Enter your current and new tire specifications to compare.
Understanding Tire and Wheel Specifications
Proper tire and wheel fitment is crucial for vehicle performance, safety, and aesthetics. This calculator helps you compare the overall diameter, section width, and sidewall height of your current tire setup versus a potential new one. This is essential when considering larger wheels, different tire profiles, or upgrades.
Key Tire and Wheel Measurements Explained:
- Tire Width (mm): The widest point of the tire from sidewall to sidewall in millimeters.
- Aspect Ratio (%): The ratio of the tire's sidewall height to its width. For example, a 55 aspect ratio means the sidewall height is 55% of the tire's width.
- Wheel Diameter (inches): The diameter of the wheel rim itself.
How the Calculator Works (The Math Behind It)
The calculator uses standard automotive engineering formulas to determine key dimensions and compare them. Here's a breakdown:
1. Sidewall Height (inches):
Sidewall Height = (Tire Width (mm) * Aspect Ratio (%) / 100) / 25.4
We divide by 100 to convert the percentage to a decimal and by 25.4 to convert millimeters to inches.
2. Section Width (inches):
Section Width = Tire Width (mm) / 25.4
This is the tire's width in inches.
3. Overall Diameter (inches):
Overall Diameter = (2 * Sidewall Height) + Wheel Diameter (inches)
This represents the total diameter of the tire and wheel assembly.
4. Comparison Metrics:
- Diameter Difference: The absolute difference in overall diameter between the new and current setup. A small difference (typically within 3%) is ideal to maintain speedometer accuracy and ABS functionality.
- Width Difference: The absolute difference in section width. This helps assess if the new tire will rub against suspension components or fenders.
- Sidewall Height Difference: The absolute difference in sidewall height.
Why This Matters for Your Vehicle:
- Speedometer and Odometer Accuracy: Significant changes in overall diameter can throw off your speedometer and odometer readings.
- Gearing: A larger overall diameter effectively changes your vehicle's gear ratio, impacting acceleration and fuel economy.
- Clearance: Ensure adequate space within the wheel wells for the new tires, especially when turning and compressing the suspension.
- ABS and Traction Control: These systems rely on wheel speed sensors. Major variations in tire diameter can confuse these systems.
- Ride Comfort: Lower aspect ratio tires (shorter sidewalls) generally provide a firmer ride, while higher aspect ratios offer more comfort.
Example Scenario:
Let's compare a common setup to a slightly larger aftermarket one:
Current Setup:
- Tire Width: 225 mm
- Aspect Ratio: 55%
- Wheel Diameter: 17 inches
New Setup:
- Tire Width: 245 mm
- Aspect Ratio: 45%
- Wheel Diameter: 18 inches
The calculator will compute the sidewall height, section width, and overall diameter for both, then highlight the differences, allowing you to make an informed decision about the potential fit and impact on your vehicle.
Fitment Comparison Summary
"; resultHtml += "Current Setup:"; resultHtml += "Overall Diameter: " + currentOverallDiameter.toFixed(2) + " inches"; resultHtml += "Section Width: " + currentSectionWidthIn.toFixed(2) + " inches"; resultHtml += "Sidewall Height: " + currentSidewallHeightIn.toFixed(2) + " inches"; resultHtml += "New Setup:"; resultHtml += "Overall Diameter: " + newOverallDiameter.toFixed(2) + " inches"; resultHtml += "Section Width: " + newSectionWidthIn.toFixed(2) + " inches"; resultHtml += "Sidewall Height: " + newSidewallHeightIn.toFixed(2) + " inches"; resultHtml += ""; resultHtml += "Differences:"; resultHtml += "Diameter Change: " + diameterDifference.toFixed(2) + " inches (" + diameterDifferencePercent.toFixed(2) + "%)"; resultHtml += "Width Change: " + widthDifference.toFixed(2) + " inches"; resultHtml += "Sidewall Change: " + sidewallDifference.toFixed(2) + " inches"; var warning = ""; if (diameterDifferencePercent > 3) { warning += "Warning: A diameter difference greater than 3% may affect speedometer accuracy and ABS functionality. "; } if (newSectionWidthIn > currentSectionWidthIn + 1.5) { // Arbitrary threshold for potential rubbing warning += "Note: The new tire is significantly wider, check for clearance issues with fenders and suspension. "; } if (newOverallDiameter < currentOverallDiameter) { warning += "Note: The new setup is smaller in overall diameter, which may impact ride height and gearing. "; } else if (newOverallDiameter > currentOverallDiameter) { warning += "Note: The new setup is larger in overall diameter, which may impact ride height and gearing. "; } fitmentResultP.innerHTML = resultHtml + "" + warning + ""; fitmentResultP.style.color = "#28a745"; // Green for success }