ET Calculator – Wheel Offset and Backspacing Calculator
Calculate wheel offset, backspacing, and fitment measurements
How to Use
- Enter your wheel width in inches
- Enter the wheel offset (ET) in millimeters
- Click calculate to see backspacing and frontspacing
- Review measurements to ensure proper fitment
What is Wheel Offset (ET)?
Wheel offset, also known as ET (from the German 'Einpresstiefe'), is the distance in millimeters from the wheel's mounting surface to the centerline of the wheel. It determines how far in or out the wheel sits in the wheel well.
Positive offset means the mounting surface is closer to the outside (street side) of the wheel. Negative offset means it's closer to the inside (brake side). Zero offset means the mounting surface is exactly at the centerline.
Backspacing vs Offset
Backspacing is the distance from the wheel's mounting surface to the inner edge of the wheel, measured in inches. While offset is measured from the centerline, backspacing is measured from the inner edge, making it easier to visualize clearance issues.
Why Wheel Offset Matters
- Prevents wheels from rubbing against fenders or suspension components
- Affects vehicle handling and steering response
- Impacts brake caliper clearance
- Influences tire wear patterns
- Changes the vehicle's track width and stance
Choosing the Right Offset
Always consult your vehicle's specifications or a wheel fitment specialist before purchasing new wheels. Incorrect offset can cause serious safety issues, premature tire wear, and damage to suspension components.
Frequently Asked Questions
- What does ET mean on wheels?
- ET stands for 'Einpresstiefe' in German, which translates to 'insertion depth.' It's the standard way to express wheel offset in millimeters. For example, ET35 means the mounting surface is 35mm from the wheel's centerline toward the outside.
- Can I use wheels with different offset than stock?
- You can, but it's important to stay within safe ranges. Typically, ±5-10mm from stock offset is acceptable, but this varies by vehicle. Larger changes may require modifications or cause clearance issues.
- What's the difference between positive and negative offset?
- Positive offset pushes the wheel inward (mounting surface closer to outside), common on front-wheel-drive cars. Negative offset pushes the wheel outward (mounting surface closer to inside), giving a wider stance but potentially causing rubbing.
- How do I measure backspacing?
- Place the wheel face-down on a flat surface. Measure from the mounting surface (where it bolts to the hub) to the inner edge of the wheel. This measurement in inches is your backspacing.