Wheel & Tire Fitment Calculator
Use this calculator to compare your current wheel and tire setup with a potential new setup. Understand how changes in tire size, rim diameter, rim width, and offset will affect your vehicle's speedometer accuracy and wheel well clearance.
Current Setup
New Setup
Calculation Results
Enter values and click "Calculate Fitment" to see results.
Current Wheel & Tire Specs:
'; resultHTML += 'Overall Tire Diameter: ' + currentOverallDiameter.toFixed(2) + ' mm'; resultHTML += 'Sidewall Height: ' + currentSidewallHeight.toFixed(2) + ' mm'; resultHTML += 'Overall Tire Circumference: ' + currentCircumference.toFixed(2) + ' mm'; resultHTML += 'New Wheel & Tire Specs:
'; resultHTML += 'Overall Tire Diameter: ' + newOverallDiameter.toFixed(2) + ' mm'; resultHTML += 'Sidewall Height: ' + newSidewallHeight.toFixed(2) + ' mm'; resultHTML += 'Overall Tire Circumference: ' + newCircumference.toFixed(2) + ' mm'; resultHTML += 'Comparison:
'; resultHTML += 'Speedometer Difference: ' + speedometerDifference.toFixed(2) + '%'; if (speedometerDifference > 0) { resultHTML += 'Your speedometer will read ' + Math.abs(speedometerDifference).toFixed(2) + '% slower than actual speed.'; } else if (speedometerDifference < 0) { resultHTML += 'Your speedometer will read ' + Math.abs(speedometerDifference).toFixed(2) + '% faster than actual speed.'; } else { resultHTML += 'Your speedometer reading will be unchanged.'; } resultHTML += 'Inner Clearance Change: ' + innerClearanceChange.toFixed(2) + ' mm'; if (innerClearanceChange > 0) { resultHTML += 'The new wheel\'s inner edge will be ' + innerClearanceChange.toFixed(2) + ' mm further from the suspension/fender liner (more clearance).'; } else if (innerClearanceChange < 0) { resultHTML += 'The new wheel\'s inner edge will be ' + Math.abs(innerClearanceChange).toFixed(2) + ' mm closer to the suspension/fender liner (less clearance). Check for rubbing!'; } else { resultHTML += 'Inner clearance will be unchanged.'; } resultHTML += 'Outer Clearance Change: ' + outerClearanceChange.toFixed(2) + ' mm'; if (outerClearanceChange > 0) { resultHTML += 'The new wheel\'s outer edge will be ' + outerClearanceChange.toFixed(2) + ' mm further out towards the fender (more poke). Check for rubbing!'; } else if (outerClearanceChange < 0) { resultHTML += 'The new wheel\'s outer edge will be ' + Math.abs(outerClearanceChange).toFixed(2) + ' mm further in from the fender (less poke).'; } else { resultHTML += 'Outer clearance will be unchanged.'; } document.getElementById('result').innerHTML = resultHTML; }Understanding Your Vehicle's Wheel and Tire Fitment
Choosing the right wheels and tires for your vehicle is crucial for performance, aesthetics, and safety. A "rim calculator" or "wheel and tire fitment calculator" helps you understand how different setups will impact your car. It's not just about looks; incorrect fitment can lead to speedometer errors, rubbing against suspension components or fender liners, and even affect handling characteristics.
Why Use a Wheel & Tire Fitment Calculator?
- Speedometer Accuracy: Changing the overall diameter of your wheel and tire package will directly affect your speedometer reading. A larger diameter will make your speedometer read slower than your actual speed, while a smaller diameter will make it read faster. This can lead to speeding tickets or inaccurate mileage tracking.
- Clearance Issues: Wheels and tires that are too wide, have an incorrect offset, or are too tall can rub against your vehicle's suspension components (struts, control arms), brake calipers, or fender liners and bodywork, especially during turns or over bumps.
- Aesthetics and Stance: The calculator helps visualize how much a new wheel will "poke" out from the fender or sit further inward, allowing you to achieve your desired stance.
- Performance: Proper fitment ensures optimal handling and prevents unforeseen issues that could compromise safety.
Key Terms Explained:
To effectively use the calculator, it's important to understand the following terms:
- Tire Width (mm): This is the first number in a tire size (e.g.,
225/45R17). It represents the width of the tire's tread in millimeters. - Aspect Ratio (%): The second number (e.g., 225/
45R17) is the sidewall height as a percentage of the tire's width. A 45 aspect ratio means the sidewall height is 45% of the 225mm tire width. - Rim Diameter (inches): The third number (e.g., 225/45R
17) indicates the diameter of the wheel rim in inches. - Rim Width (inches): This is the measurement of the rim from bead seat to bead seat, typically expressed in inches (e.g.,
7.5J). A wider rim can accommodate a wider tire, but also affects clearance. - Offset (ET, mm): Offset is the distance from the hub mounting surface to the centerline of the wheel.
- Positive Offset: The hub mounting surface is towards the front (outboard) side of the wheel's centerline. This moves the wheel further inward towards the suspension. Most modern front-wheel-drive cars have positive offset.
- Negative Offset: The hub mounting surface is towards the back (inboard) side of the wheel's centerline. This moves the wheel further outward from the suspension, creating a "deeper dish" look. Common on older cars or off-road vehicles.
- Zero Offset: The hub mounting surface is exactly at the centerline of the wheel.
How to Interpret the Results:
- Speedometer Difference: A small percentage (e.g., less than +/- 3%) is generally acceptable, but always be aware of the actual speed vs. indicated speed.
- Inner Clearance Change:
- Positive value: The new wheel's inner edge is further away from the suspension/inner fender. This means more clearance, which is generally good.
- Negative value: The new wheel's inner edge is closer to the suspension/inner fender. This indicates less clearance and a higher risk of rubbing.
- Outer Clearance Change:
- Positive value: The new wheel's outer edge extends further out towards the fender. This means more "poke" and a higher risk of rubbing against the fender lip, especially when turning or with suspension compression.
- Negative value: The new wheel's outer edge sits further inward from the fender. This means less "poke" and generally more fender clearance.
Important Considerations:
While this calculator provides valuable insights, it's a theoretical tool. Always perform a physical test fit if possible, especially with significant changes. Factors like suspension sag, tire bulge, and specific vehicle geometry can influence actual fitment. Also, be mindful of local regulations regarding wheel poke and tire coverage.