Wheel ET (Offset) Calculator
Compare your current wheel setup to a new setup and instantly see how inner clearance, outer poke, and track width change.
Tip: Spacer reduces effective offset. Example: ET35 with a 10 mm spacer behaves like ET25.
What does ET mean on wheels?
ET is the wheel offset measurement in millimeters. It describes how far the wheel mounting face sits from the wheel centerline. You will often see it listed as ET35, ET45, and so on.
- Higher ET usually pulls the wheel inward (closer to suspension components).
- Lower ET usually pushes the wheel outward (more fender poke).
- Negative ET is very aggressive and common on some off-road or deep-dish applications.
Because wheel width and ET work together, using an ET calculator for wheels is the easiest way to compare old vs new fitment before buying.
How this ET calculator wheels tool works
Inputs used
- Current wheel width and ET offset
- New wheel width and ET offset
- Optional spacer thickness on the new setup
Core geometry formulas
The calculator converts wheel width from inches to millimeters and then computes the inner and outer wheel lip positions relative to the hub:
- Inner position = (width in mm / 2) + offset
- Outer position = (width in mm / 2) - offset
- Effective new offset = new ET - spacer
From there, it reports how far the new setup moves toward suspension (inner change), toward fender (outer change), and the centerline/track shift.
How to read the results
Inner clearance change
If inner change is positive, the new wheel sits closer to your strut, control arm, or inner liner. This means less clearance and a higher chance of rubbing. Negative inner change means improved inner room.
Outer poke change
Positive outer change means the wheel sticks out farther toward the fender. This can look great, but may require fender rolling, camber adjustment, or narrower tires.
Track width change
Track width changes mostly with effective offset. Lowering ET pushes each wheel outward, increasing total track width. Wider track can improve visual stance and sometimes cornering feel, but can also increase scrub radius effects and steering kickback.
Practical wheel fitment checklist
- Check brake caliper clearance (spoke design matters, not just ET).
- Verify inner strut and suspension arm clearance at full steering lock.
- Check outer fender clearance under compression (passengers + bumps).
- Confirm tire size and sidewall shape for your wheel width.
- If using spacers, use hub-centric parts and proper bolt/stud length.
- After installation, re-torque wheel hardware and test drive carefully.
Example: ET45 8" to ET35 9"
This is a common upgrade path for a sportier stance. Although ET35 sounds only 10 mm lower, the extra wheel width also changes both inner and outer lip positions. The result is often significantly more outer poke than expected by ET alone. That is exactly why this calculator compares full wheel geometry, not just offset values.
Final notes
Use this ET calculator wheels page as a planning tool before purchasing wheels, tires, or spacers. Always measure your own vehicle, because suspension setup, ride height, tire brand shape, and alignment specs can change real-world fitment. The safest approach is to combine math with a physical test fit when possible.