Wheel Tire Offset Calculator

Wheel & Tire Offset Calculator

Use this calculator to compare your current wheel and tire setup with a potential new setup. It will show you how much the inner and outer edges of your wheels and tires will move, helping you determine clearance with suspension components and fenders.

Enter your wheel and tire specifications above and click "Calculate Changes" to see the results.

function calculateWheelOffset() { var originalWheelWidth = parseFloat(document.getElementById('originalWheelWidth').value); var originalWheelOffset = parseFloat(document.getElementById('originalWheelOffset').value); var originalTireWidth = parseFloat(document.getElementById('originalTireWidth').value); var newWheelWidth = parseFloat(document.getElementById('newWheelWidth').value); var newWheelOffset = parseFloat(document.getElementById('newWheelOffset').value); var newTireWidth = parseFloat(document.getElementById('newTireWidth').value); var resultDiv = document.getElementById('calculationResult'); var inchToMm = 25.4; if (isNaN(originalWheelWidth) || isNaN(originalWheelOffset) || isNaN(originalTireWidth) || isNaN(newWheelWidth) || isNaN(newWheelOffset) || isNaN(newTireWidth) || originalWheelWidth <= 0 || newWheelWidth <= 0 || originalTireWidth <= 0 || newTireWidth <= 0) { resultDiv.innerHTML = 'Please enter valid positive numbers for all fields.'; return; } // Convert wheel widths to mm var originalWheelWidthMm = originalWheelWidth * inchToMm; var newWheelWidthMm = newWheelWidth * inchToMm; // Calculate half widths var originalWheelHalfWidthMm = originalWheelWidthMm / 2; var newWheelHalfWidthMm = newWheelWidthMm / 2; var originalTireHalfWidthMm = originalTireWidth / 2; var newTireHalfWidthMm = newTireWidth / 2; // — Wheel Edge Calculations — // Distance from Hub Mounting Surface (HMS) to the inner edge of the wheel // Positive offset means HMS is further outboard from centerline, so inner edge is further from HMS var originalWheelInnerEdgeDist = originalWheelHalfWidthMm + originalWheelOffset; var newWheelInnerEdgeDist = newWheelHalfWidthMm + newWheelOffset; // Distance from HMS to the outer edge of the wheel // Positive offset means HMS is further outboard from centerline, so outer edge is closer to HMS var originalWheelOuterEdgeDist = originalWheelHalfWidthMm – originalWheelOffset; var newWheelOuterEdgeDist = newWheelHalfWidthMm – newWheelOffset; // Change in Wheel Inner Edge Position // Positive value means inner edge moved OUTWARD (away from suspension) = MORE inner clearance // Negative value means inner edge moved INWARD (towards suspension) = LESS inner clearance var wheelInnerEdgeChange = newWheelInnerEdgeDist – originalWheelInnerEdgeDist; // Change in Wheel Outer Edge Position // Positive value means outer edge moved OUTWARD (towards fender) = LESS outer clearance (more "poke") // Negative value means outer edge moved INWARD (away from fender) = MORE outer clearance var wheelOuterEdgeChange = newWheelOuterEdgeDist – originalWheelOuterEdgeDist; // — Tire Edge Calculations (assuming tire centerline aligns with wheel centerline) — // Distance from HMS to the inner edge of the tire var originalTireInnerEdgePos = originalWheelOffset – originalTireHalfWidthMm; var newTireInnerEdgePos = newWheelOffset – newTireHalfWidthMm; // Distance from HMS to the outer edge of the tire var originalTireOuterEdgePos = originalWheelOffset + originalTireHalfWidthMm; var newTireOuterEdgePos = newWheelOffset + newTireHalfWidthMm; // Change in Tire Inner Edge Position // Positive value means inner tire edge moved OUTWARD (away from suspension) = MORE inner clearance // Negative value means inner tire edge moved INWARD (towards suspension) = LESS inner clearance var tireInnerEdgeChange = newTireInnerEdgePos – originalTireInnerEdgePos; // Change in Tire Outer Edge Position // Positive value means outer tire edge moved OUTWARD (towards fender) = LESS outer clearance (more "poke") // Negative value means outer tire edge moved INWARD (away from fender) = MORE outer clearance var tireOuterEdgeChange = newTireOuterEdgePos – originalTireOuterEdgePos; var resultsHtml = '

Comparison Results:

'; resultsHtml += 'Wheel Edge Movement:'; resultsHtml += '

'; resultsHtml += '
• Inner Wheel Edge: 0 ? '#28a745' : (wheelInnerEdgeChange ' + wheelInnerEdgeChange.toFixed(2) + ' mm ' + (wheelInnerEdgeChange > 0 ? 'outward (more inner clearance)' : (wheelInnerEdgeChange < 0 ? 'inward (less inner clearance)' : '(no change)')) + '
'; resultsHtml += '
• Outer Wheel Edge: 0 ? '#dc3545' : (wheelOuterEdgeChange ' + wheelOuterEdgeChange.toFixed(2) + ' mm ' + (wheelOuterEdgeChange > 0 ? 'outward (less outer clearance / more poke)' : (wheelOuterEdgeChange < 0 ? 'inward (more outer clearance)' : '(no change)')) + '
'; resultsHtml += '

'; resultsHtml += 'Tire Edge Movement:'; resultsHtml += '

'; resultsHtml += '
• Inner Tire Edge: 0 ? '#28a745' : (tireInnerEdgeChange ' + tireInnerEdgeChange.toFixed(2) + ' mm ' + (tireInnerEdgeChange > 0 ? 'outward (more inner clearance)' : (tireInnerEdgeChange < 0 ? 'inward (less inner clearance)' : '(no change)')) + '
'; resultsHtml += '
• Outer Tire Edge: 0 ? '#dc3545' : (tireOuterEdgeChange ' + tireOuterEdgeChange.toFixed(2) + ' mm ' + (tireOuterEdgeChange > 0 ? 'outward (less outer clearance / more poke)' : (tireOuterEdgeChange < 0 ? 'inward (more outer clearance)' : '(no change)')) + '
'; resultsHtml += '

'; resultDiv.innerHTML = resultsHtml; }

Understanding Wheel and Tire Offset

Wheel offset is a critical measurement that determines how your wheels and tires sit within your vehicle's fender wells. It's the distance from the hub mounting surface to the centerline of the wheel. Understanding offset is crucial when choosing new wheels or tires, as it directly impacts clearance, handling, and aesthetics.

Types of Offset:

• Positive Offset: The hub mounting surface is towards the front (outboard) side of the wheel's centerline. Most front-wheel-drive cars and newer rear-wheel-drive cars have positive offset wheels. This tucks the wheel further into the fender.
• Negative Offset: The hub mounting surface is towards the back (inboard) side of the wheel's centerline. This pushes the wheel further out from the fender, often seen on older trucks or off-road vehicles.
• Zero Offset: The hub mounting surface is exactly aligned with the wheel's centerline.

Why Offset Matters:

• Fender Clearance: Too much negative offset or a wider wheel can cause the tire to rub against the fender lip, especially during turns or suspension compression.
• Suspension Clearance: Too much positive offset or a wider wheel can cause the inner edge of the tire or wheel to rub against suspension components (struts, control arms) or brake calipers.
• Handling Characteristics (Scrub Radius): Offset affects the scrub radius, which is the distance between the steering axis and the center of the tire's contact patch. Changing this can alter steering feel, stability, and even tire wear.
• Bearing Wear: Significant changes in offset can increase the load on wheel bearings, potentially leading to premature wear.
• Aesthetics: Offset plays a huge role in how "flush" your wheels sit with the fenders, contributing to the overall look of your vehicle.

How Wheel Width and Tire Width Affect Clearance:

It's not just offset; wheel width and tire width are equally important. A wider wheel, even with the same offset, will extend further both inward and outward. A wider tire will also add to the overall width, potentially causing rubbing issues even if the wheel fits perfectly.

This calculator helps you visualize these changes. For example, if the calculator shows the inner wheel edge moving 5mm inward, it means you have 5mm less clearance between your wheel and suspension components. If the outer tire edge moves 10mm outward, your tire will be 10mm closer to your fender lip.

Using the Calculator:

Input your current wheel width (in inches), offset (in millimeters), and tire width (in millimeters). Then, enter the specifications for the new setup you are considering. The calculator will provide precise measurements of how much the inner and outer edges of both your wheel and tire will shift. Always double-check your vehicle's specific clearance requirements and consider professional advice before making significant changes.