Wheel Offset Calculator

What Is Wheel Offset?

Wheel offset is the distance between the wheel’s centerline and the mounting surface that bolts to the hub.

It is measured in millimeters (mm) and usually shown as ET.

There are three common types:

• Positive offset
  The mounting surface is closer to the outside of the wheel. The wheel sits further inside the arch. Most modern cars use this.
• Zero offset
  The mounting surface is exactly in the middle of the wheel.
• Negative offset
  The mounting surface is closer to the inside. The wheel sticks out more.

Even a small offset change, such as 5–10 mm, can noticeably affect clearance and appearance.

Why Wheel Offset Matters

Wheel offset affects more than looks. It directly impacts safety and drivability.

Here is what can happen if offset is wrong:

• The wheel can rub on suspension parts like struts or coilovers
• The tire can hit the fender during turns or bumps
• Steering feel can change
• Wheel bearings can wear faster
• The car may fail inspection in some regions

A wheel offset calculator helps you see these risks before you buy or install anything.

What a Wheel Offset Calculator Does

The calculator compares your current wheel setup with a new wheel setup.

It answers two key questions:

1. How much closer or further the inner edge of the wheel moves
2. How much the outer edge moves toward or away from the fender

This makes it easier to judge suspension clearance and fender flushness.

Inputs Used in the Calculator

The calculator you shared uses four inputs:

Current Setup

• Width (inches)
• Offset (ET in mm)

New Setup

• Width (inches)
• Offset (ET in mm)

Wheel width is entered in inches because that is how wheels are commonly sold. Offset stays in millimeters, which matches industry standards.

Behind the scenes, the calculator converts inches to millimeters so all measurements line up correctly.

How the Calculator Works (Plain English)

Here is what happens step by step:

1. The tool converts wheel widths from inches to millimeters
2. It finds the centerline of each wheel
3. It calculates:
   • The inner position (near suspension)
   • The outer position (near fender)
4. It compares the new wheel to the current one
5. It shows the difference in millimeters

You do not need to understand the math to use it. The results are explained in simple language.

Understanding the Results

Inner Clearance

This shows how the inner edge of the new wheel moves compared to your current wheel.

• More room inside
  The wheel moves away from the suspension. This is generally safe.
• Less room inside
  The wheel moves closer to the strut or coilover. This needs careful checking.

The calculator highlights this clearly and even gives a warning if clearance is reduced.

Outer Position

This shows how the outer edge of the wheel changes.

• Pokes out more
  The wheel moves outward toward the fender. This can look aggressive but may cause rubbing.
• Retracts inward
  The wheel sits deeper inside the wheel arch.

This helps you judge whether the setup will look flush, tucked, or too aggressive.

Visual Comparison Bar

One of the most helpful parts of the calculator is the visual bar.

• Gray shows your current wheel
• Blue shows the new wheel
• The center line represents the hub face

This makes it easy to see the difference at a glance, even if you are not comfortable with numbers.

Fitment Notes Explained

The calculator also provides written notes such as:

• Warnings about suspension clearance
• Notes about fender poke or retraction

These notes translate measurements into real-world advice, which is especially useful for beginners.

When to Use a Wheel Offset Calculator

This tool is useful in many situations:

• Buying aftermarket wheels
• Switching to wider wheels
• Changing offset for a flush look
• Adding or removing spacers
• Comparing factory wheels to custom setups

If you are unsure whether a wheel will fit, this calculator should be one of your first steps.

Common Mistakes the Calculator Helps Avoid

• Assuming wider wheels always fit with the same offset
• Ignoring inner clearance and only focusing on looks
• Guessing spacer size instead of measuring
• Copying another car’s setup without checking differences

Using actual numbers removes guesswork.