et offset calculator

What is ET offset?

ET offset is the distance between a wheel’s mounting surface and its centerline, expressed in millimeters. ET comes from the German term Einpresstiefe. If you are comparing wheels, understanding ET is essential because even a small offset change can significantly alter inner clearance and outer “poke.”

• Higher ET generally pulls the wheel inward (toward suspension).
• Lower ET generally pushes the wheel outward (toward fender).
• Negative ET pushes the wheel outward even more and is common in aggressive off-road setups.

How this ET offset calculator works

This calculator compares your old and new wheel geometry using wheel width, ET value, and optional spacer thickness. It outputs practical fitment values, including how much the wheel will stick out and how much inner clearance changes.

Core formulas used

• Width in mm = width in inches × 25.4
• Effective ET = new ET − spacer thickness
• Outer position = half width − ET
• Inner position = half width + ET
• Change = new value − old value

From these, we can tell whether the new wheel sits further outside, further inside, or closer to suspension components such as struts and control arms.

How to use the calculator

1) Enter your current setup

Start with your current wheel width and ET offset. This is your baseline.

2) Enter your new wheel specs

Add the width and ET of the wheel you want to install. If you plan to use spacers, enter spacer thickness too.

3) Review the output carefully

Focus on these two values first:

• Outer change (poke): positive means the wheel sits further out.
• Inner clearance change: positive “closer to suspension” is riskier for rubbing.

Practical interpretation of results

People often chase flush fitment, but safe fitment is the priority. A setup that looks perfect at static ride height can still rub while turning, hitting bumps, or with passengers in the car.

• If outer poke increases a lot, fender rubbing risk increases.
• If inner clearance decreases, strut or control arm interference risk increases.
• Spacer use can solve inner clearance issues but may worsen fender clearance.

Common ET offset mistakes to avoid

Ignoring tire size

Wheel fitment is only half the equation. A wider tire can eliminate a clearance margin even when wheel math appears safe.

Assuming all “same size” tires are identical

Tire brands measure differently. One 255 tire may be noticeably wider than another 255.

Skipping dynamic checks

Always test lock-to-lock steering, full suspension compression, and loaded conditions. Static garage checks are not enough.

ET offset FAQ

Is lower ET always better?

No. Lower ET creates a wider stance but can cause fender rub, steering scrub changes, and extra wheel bearing load if taken too far.

Do spacers change ET?

Yes. Spacers reduce effective ET by their thickness. For example, ET40 with a 5 mm spacer behaves like ET35.

How much offset change is usually safe?

There is no universal number. Vehicle geometry, tire shape, suspension setup, and alignment matter. Use this calculator for geometry estimates, then confirm with real fitment checks.

Final takeaway

An ET offset calculator helps you make smarter fitment decisions before spending money on wheels and tires. By understanding inner clearance and outer poke together—not separately—you reduce rubbing risk and avoid expensive trial-and-error.