Stance & Suspension
Wheel Offset & Fender Poke Visualizer
Calculate strut clearance and outer fender poke when changing wheel widths (J) and ET offsets.
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How to Use This Tool
- Enter your stock wheel width (inches) and offset (ET in mm).
- Enter your new wheel width and offset.
- Positive inner delta means the new wheel sits closer to the strut/coilover.
- Positive outer delta means the new wheel pokes further toward the fender lip.
- Optional: subtract spacer thickness from ET to model slip-on spacers before buying.
The Formula & Physics Behind the Math
Inner edge distance from wheel centerline = (width × 25.4) ÷ 2 + offset (mm). Outer edge distance = (width × 25.4) ÷ 2 − offset (mm). Comparing stock vs. new inner/outer distances yields clearance and poke deltas. Backspacing ≈ (width + 1) ÷ 2 + offset ÷ 25.4 inches. Lower ET (or spacers) moves the wheel outward; higher ET tucks it in. Always confirm with a dry fit — hub-centric rings, brake caliper clearance, and rolled fenders change the real outcome.
Frequently Asked Questions
What does ET offset mean?
ET is the distance in millimeters from the wheel mounting surface to the centerline. Lower ET pushes the wheel outward; higher ET tucks it inward.
What is the difference between offset and backspacing?
Offset (ET) is measured from the centerline in millimeters. Backspacing is the distance from the mounting pad to the inner lip in inches. Both describe the same geometry — this calculator reports both so you can match either catalog format.
Will spacers change these numbers?
Yes. Wheel spacers effectively reduce ET (push the wheel out). Subtract spacer thickness from ET when modeling a spaced setup, and confirm lug stud engagement with the Wheel Spacer Calculator.
Does this account for camber or rolled fenders?
No. This is a 2D cross-section estimate. Negative camber, tire width/sidewall, and fender rolling all change real-world clearance — dry-fit before you torque anything.
How do I avoid rubbing after a wider wheel?
Watch the outer poke delta and leave margin for suspension compression and steering lock. If poke grows more than a few millimeters, plan for shorter springs, camber plates, or a rolled fender lip.