Free wheel fitment tool
Wheel Fitment Calculator — Offset, Backspacing and Clearance
Compare stock vs aftermarket wheels — offset change, poke, backspacing and fender clearance in one check.
Will These Wheels Fit?
Stock vs new wheel specs.
Wheel Offset Explained
Offset (ET) is the distance in mm from the wheel’s centerline to its mounting face. Lower offset = wheel sticks out more. ET45 to ET35 moves the wheel 10mm outward.
Backspacing vs Offset
- Backspacing = distance from mounting face to the inner lip. More backspacing = tucks inward.
- Formula: backspacing = (width x 25.4 / 2) + offset.
- Too little backspacing hits fenders; too much hits suspension and struts.
Fitment Rules of Thumb
- Stay within ±10mm offset of stock for zero-drama fitment.
- Poke beyond the fender looks aggressive but throws road grime and may be illegal.
- Bigger offset changes alter scrub radius — steering feel and tramlining change.
Frequently Asked Questions
What does ET35 mean on a wheel?
ET35 = 35mm positive offset — the mounting face sits 35mm outboard of the wheel’s centerline. Lower ET pushes wheels outward.
Will a lower offset cause rubbing?
It can — the outer edge moves toward the fender. The calculator above checks your available clearance.
How much offset change is safe?
Within ±10mm of stock is safe on most cars. Beyond 15mm, check clearance at full steering lock and over bumps.
Do I need hub-centric rings?
If the new wheel’s center bore is larger than your hub, yes — rings prevent vibration. Never rely on lug nuts to center the wheel.
Can wrong offset damage my car?
Extreme changes stress wheel bearings, alter handling, and can rub through brake lines or fender liners. Stay close to stock.
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