Tire Offset Calculator

Tire Offset Change Calculator

Results will appear here.

function calculateOffsetChange() { var currentWheelWidth = parseFloat(document.getElementById("currentWheelWidth").value); var currentWheelOffset = parseFloat(document.getElementById("currentWheelOffset").value); var newWheelWidth = parseFloat(document.getElementById("newWheelWidth").value); var newWheelOffset = parseFloat(document.getElementById("newWheelOffset").value); if (isNaN(currentWheelWidth) || isNaN(currentWheelOffset) || isNaN(newWheelWidth) || isNaN(newWheelOffset) || currentWheelWidth <= 0 || newWheelWidth <= 0) { document.getElementById("offsetResult").innerHTML = "Please enter valid positive numbers for all fields."; return; } var INCH_TO_MM = 25.4; // Calculate current wheel's inner and outer edge positions relative to the mounting surface var currentHalfWidthMM = (currentWheelWidth / 2) * INCH_TO_MM; var currentInnerEdgePos = currentHalfWidthMM + currentWheelOffset; // Distance from mounting surface to inner edge var currentOuterEdgePos = currentHalfWidthMM – currentWheelOffset; // Distance from mounting surface to outer edge // Calculate new wheel's inner and outer edge positions relative to the mounting surface var newHalfWidthMM = (newWheelWidth / 2) * INCH_TO_MM; var newInnerEdgePos = newHalfWidthMM + newWheelOffset; // Distance from mounting surface to inner edge var newOuterEdgePos = newHalfWidthMM – newWheelOffset; // Distance from mounting surface to outer edge // Calculate changes var changeInnerClearance = currentInnerEdgePos – newInnerEdgePos; // Positive means more inner clearance, negative means less var changeOuterPoke = newOuterEdgePos – currentOuterEdgePos; // Positive means more outer poke, negative means less var resultHTML = "Change in Inner Clearance: "; if (changeInnerClearance > 0) { resultHTML += Math.abs(changeInnerClearance).toFixed(2) + " mm further from suspension/inward (more clearance)"; } else if (changeInnerClearance < 0) { resultHTML += Math.abs(changeInnerClearance).toFixed(2) + " mm closer to suspension/inward (less clearance)"; } else { resultHTML += "No change in inner clearance."; } resultHTML += "Change in Outer Poke: "; if (changeOuterPoke > 0) { resultHTML += Math.abs(changeOuterPoke).toFixed(2) + " mm further outward (more poke)"; } else if (changeOuterPoke < 0) { resultHTML += Math.abs(changeOuterPoke).toFixed(2) + " mm further inward (less poke)"; } else { resultHTML += "No change in outer poke."; } document.getElementById("offsetResult").innerHTML = resultHTML; }

Understanding Wheel Offset and Its Impact

When upgrading or replacing your vehicle's wheels, understanding wheel offset is crucial. It's not just about aesthetics; offset significantly impacts your vehicle's handling, tire clearance, and even the longevity of suspension components. Our Tire Offset Change Calculator helps you predict how new wheels will fit compared to your current setup.

What is Wheel Offset?

Wheel offset is the distance from the wheel's mounting surface (the part that bolts to the hub) to the true centerline of the wheel. It is typically measured in millimeters (mm) and can be positive, negative, or zero.

  • Positive Offset: The mounting surface is located outboard (towards the street side) of the wheel's centerline. Most modern front-wheel-drive cars and many rear-wheel-drive cars have positive offset wheels. This design helps keep the wheel tucked into the fender well.
  • Negative Offset: The mounting surface is located inboard (towards the vehicle's suspension/frame) of the wheel's centerline. This pushes the wheel further out from the vehicle, often seen on older trucks, off-road vehicles, or for a "deep dish" look.
  • Zero Offset: The mounting surface is exactly aligned with the wheel's centerline.

Why is Offset Important?

Changing your wheel's offset, especially when combined with a different wheel width, can have several consequences:

  • Fender Clearance: If the new wheels poke out too much (more negative offset or wider wheel), they might rub against the fender, especially during turns or suspension compression.
  • Suspension/Brake Clearance: If the new wheels tuck in too much (more positive offset or wider wheel), the inner edge of the tire or wheel might rub against suspension components (struts, control arms) or brake calipers.
  • Handling Characteristics: Significant changes in offset can alter the scrub radius, affecting steering feel, stability, and tire wear.
  • Aesthetics: Offset plays a major role in how flush your wheels sit with the fenders.

How Our Calculator Helps

This calculator takes your current wheel's width and offset, along with the proposed new wheel's width and offset, to determine two critical changes:

  1. Change in Inner Clearance: This tells you how much closer or further the inner edge of your new wheel/tire will be to your vehicle's suspension components or inner fender well. A negative value here means less inner clearance, increasing the risk of rubbing.
  2. Change in Outer Poke: This indicates how much further out or in the outer edge of your new wheel/tire will sit relative to your fender. A positive value means the wheel will "poke" out more, potentially causing fender rubbing or requiring fender modifications.

Example Scenario:

Let's say your current wheels are 8.0 inches wide with a +35mm offset. You're considering new wheels that are 9.0 inches wide with a +25mm offset.

Using the calculator:

  • Current Wheel Width: 8.0 inches
  • Current Wheel Offset: 35 mm
  • New Wheel Width: 9.0 inches
  • New Wheel Offset: 25 mm

The calculator would show:

  • Change in Inner Clearance: Approximately -2.70 mm (meaning the new wheel's inner edge moves 2.70 mm closer to the suspension/inward, reducing inner clearance).
  • Change in Outer Poke: Approximately +22.70 mm (meaning the new wheel's outer edge moves 22.70 mm further outward, increasing poke).

This example indicates that while the new wheels will poke out significantly more (which might be the desired aesthetic), you also need to check carefully for potential rubbing on the inside, as you're losing a small amount of inner clearance.

Always double-check measurements on your specific vehicle, as even small changes can sometimes lead to clearance issues. This calculator provides a valuable estimate to guide your wheel selection process.

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