Rim Offset Calculator

Use this calculator to compare how a new wheel setup will sit relative to your current wheels. It helps determine if your new wheels will extend further out, tuck further in, or affect inner clearance.

Current Wheel Specifications

Current Rim Width (inches):

Current Offset (mm):

New Wheel Specifications

New Rim Width (inches):

New Offset (mm):

function calculateRimOffset() { var oldRimWidthInches = parseFloat(document.getElementById('oldRimWidth').value); var oldOffsetMM = parseFloat(document.getElementById('oldOffset').value); var newRimWidthInches = parseFloat(document.getElementById('newRimWidth').value); var newOffsetMM = parseFloat(document.getElementById('newOffset').value); var resultDiv = document.getElementById('rimOffsetResult'); resultDiv.innerHTML = "; // Clear previous results if (isNaN(oldRimWidthInches) || isNaN(oldOffsetMM) || isNaN(newRimWidthInches) || isNaN(newOffsetMM)) { resultDiv.innerHTML = 'Please enter valid numbers for all fields.'; return; } // Convert rim width from inches to millimeters var oldRimWidthMM = oldRimWidthInches * 25.4; var newRimWidthMM = newRimWidthInches * 25.4; // Calculate distance from hub mounting surface to inner and outer edges for old wheel // Inner clearance: (half rim width) + offset (positive offset pushes hub out, so inner edge moves further in) // Outer clearance: (half rim width) – offset (positive offset pushes hub out, so outer edge moves further in) var oldInnerClearance = (oldRimWidthMM / 2) + oldOffsetMM; var oldOuterClearance = (oldRimWidthMM / 2) – oldOffsetMM; // Calculate distance from hub mounting surface to inner and outer edges for new wheel var newInnerClearance = (newRimWidthMM / 2) + newOffsetMM; var newOuterClearance = (newRimWidthMM / 2) – newOffsetMM; // Calculate the change in position var outerEdgeChange = newOuterClearance – oldOuterClearance; var innerEdgeChange = newInnerClearance – oldInnerClearance; var outputHTML = '

Comparison Results:

'; // Outer Edge Comparison if (outerEdgeChange > 0) { outputHTML += 'The outer edge of the new wheel will extend ' + outerEdgeChange.toFixed(2) + ' mm further out compared to your current wheel.'; } else if (outerEdgeChange < 0) { outputHTML += 'The outer edge of the new wheel will retract ' + Math.abs(outerEdgeChange).toFixed(2) + ' mm further in compared to your current wheel.'; } else { outputHTML += 'The outer edge of the new wheel will be in the same position as your current wheel.'; } // Inner Edge Comparison if (innerEdgeChange > 0) { outputHTML += 'The inner edge of the new wheel will extend ' + innerEdgeChange.toFixed(2) + ' mm further in towards the suspension/fender liner compared to your current wheel.'; } else if (innerEdgeChange < 0) { outputHTML += 'The inner edge of the new wheel will retract ' + Math.abs(innerEdgeChange).toFixed(2) + ' mm further out away from the suspension/fender liner compared to your current wheel.'; } else { outputHTML += 'The inner edge of the new wheel will be in the same position as your current wheel.'; } resultDiv.innerHTML = outputHTML; } .rim-offset-calculator-container { font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; background-color: #f9f9f9; padding: 25px; border-radius: 10px; box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1); max-width: 700px; margin: 30px auto; border: 1px solid #e0e0e0; } .rim-offset-calculator-container h2 { color: #333; text-align: center; margin-bottom: 20px; font-size: 28px; } .rim-offset-calculator-container h3 { color: #555; margin-top: 25px; margin-bottom: 15px; border-bottom: 1px solid #eee; padding-bottom: 8px; font-size: 22px; } .rim-offset-calculator-container p { color: #666; line-height: 1.6; margin-bottom: 15px; } .calculator-form .form-group { margin-bottom: 18px; display: flex; flex-direction: column; } .calculator-form label { font-weight: bold; margin-bottom: 8px; color: #444; font-size: 16px; } .calculator-form input[type="number"] { width: 100%; padding: 12px; border: 1px solid #ccc; border-radius: 6px; font-size: 16px; box-sizing: border-box; transition: border-color 0.3s ease; } .calculator-form input[type="number"]:focus { border-color: #007bff; outline: none; box-shadow: 0 0 0 3px rgba(0, 123, 255, 0.25); } .calculator-form button { background-color: #007bff; color: white; padding: 14px 25px; border: none; border-radius: 6px; cursor: pointer; font-size: 18px; font-weight: bold; margin-top: 20px; width: 100%; transition: background-color 0.3s ease, transform 0.2s ease; } .calculator-form button:hover { background-color: #0056b3; transform: translateY(-2px); } .calculator-result { margin-top: 30px; padding: 20px; background-color: #e9f7ff; border: 1px solid #b3e0ff; border-radius: 8px; font-size: 17px; color: #333; } .calculator-result h3 { color: #0056b3; margin-top: 0; border-bottom: none; padding-bottom: 0; font-size: 20px; } .calculator-result p { margin-bottom: 10px; color: #333; } .calculator-result p strong { color: #0056b3; } @media (max-width: 600px) { .rim-offset-calculator-container { padding: 15px; margin: 20px auto; } .rim-offset-calculator-container h2 { font-size: 24px; } .rim-offset-calculator-container h3 { font-size: 20px; } .calculator-form button { padding: 12px 20px; font-size: 16px; } }

Understanding Wheel Offset: A Comprehensive Guide

Wheel offset, often referred to as ET (from the German "Einpresstiefe"), is a critical measurement that determines how your wheels sit within your vehicle's wheel wells. It's the distance from the hub mounting surface to the true centerline of the wheel. Understanding offset is crucial when upgrading wheels, as it directly impacts vehicle aesthetics, tire clearance, suspension geometry, and even handling characteristics.

What is Wheel Offset?

Imagine a line running perfectly through the middle of your wheel's width – that's the centerline. The hub mounting surface is where the wheel bolts to your car's hub. Offset is the distance between these two points, measured in millimeters (mm).

Positive Offset: The hub mounting surface is towards the front (outboard) side of the wheel's centerline. Most modern front-wheel-drive cars and many rear-wheel-drive cars use positive offset wheels. A higher positive offset means the wheel sits further inward towards the vehicle's body.
Negative Offset: The hub mounting surface is towards the back (inboard) side of the wheel's centerline. This is common on older vehicles, trucks, and some off-road applications. A negative offset pushes the wheel further out from the vehicle's body.
Zero Offset: The hub mounting surface is exactly aligned with the wheel's centerline.

Why is Offset Important?

Changing your wheel's offset, even by a few millimeters, can have significant consequences:

Tire Clearance: Incorrect offset can cause tires to rub against suspension components (too much positive offset) or fender liners/fenders (too much negative offset or wider wheels).
Suspension Geometry: Offset affects the scrub radius, which is the distance between the steering axis pivot point and the center of the tire's contact patch. An altered scrub radius can impact steering feel, stability, and 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.
Brake Clearance: Some brake calipers, especially larger aftermarket ones, require specific offsets to clear the wheel spokes.

How to Use the Rim Offset Calculator

Our Rim Offset Calculator helps you visualize the impact of changing your wheel setup. Here's how to use it:

Current Rim Width (inches): Enter the width of your existing wheels. This is usually stamped on the wheel or found in your vehicle's specifications.
Current Offset (mm): Input the offset of your current wheels. This is often stamped on the back of the wheel (e.g., ET35).
New Rim Width (inches): Enter the width of the new wheels you are considering.
New Offset (mm): Input the offset of the new wheels.
Calculate Offset Change: Click the button to see the results.

The calculator will tell you precisely how much further in or out both the inner and outer edges of your new wheels will sit compared to your old ones. This information is vital for checking potential rubbing issues with suspension components (inner edge) or fenders (outer edge).

Example Scenario:

Let's say your current wheels are 8.0 inches wide with an ET35 offset. You're looking at new wheels that are 9.0 inches wide with an ET25 offset.

Current Wheel: 8.0″ width, +35mm offset
New Wheel: 9.0″ width, +25mm offset

Using the calculator, you would find:

The outer edge of the new wheel will extend approximately 15.70 mm further out.
The inner edge of the new wheel will extend approximately 10.70 mm further in towards the suspension.

This means the new wheels will poke out more from the fender and also sit closer to your suspension components. You'd then need to check if 15.70mm of additional poke is acceptable for your fenders and if 10.70mm closer to the suspension will cause any rubbing.

Tips for Choosing New Wheels:

Measure Carefully: Before purchasing, measure the available clearance in your wheel wells, especially if you're making significant changes.
Consider Tire Size: A wider wheel often means a wider tire, which also impacts clearance.
Test Fit (if possible): The best way to ensure fitment is to test fit a wheel and tire combination before committing.
Consult Experts: If unsure, consult with a reputable wheel and tire specialist.

By using this Rim Offset Calculator, you can make informed decisions about your wheel upgrades, ensuring a perfect fit and maintaining your vehicle's performance and safety.