Engineering Calculator
Wheel Offset Calculator (ET) & Fitment Tool
Calculate wheel poke, inner clearance, track-width change and suspension fitment instantly. Compare wheel width and ET offset side-by-side with a premium engineering diagram.
Current wheel
New wheel
Inner change
-8.7 mm
More inner clearance
Outer change (poke)
+21.3 mm
Pokes outward
Track width change
+42.7 mm
Total across axle
ET delta
-15 mm
Fitment warnings
- Wheel pokes outward — check fender clearance and local fender-cover laws.
Visual fitment diagram
Side profile of both wheels viewed from above the axle. The dashed vertical line is the wheel centerline; the orange marker is the hub mounting face. Suspension is on the left, fender on the right.
Suspension clearance preview
Head-on viewThe tire shifts laterally as you change ET and width. The colored zones flag where the tire starts encroaching on the strut (inside) or the fender lip (outside). Always verify at full lock and full bump before driving.
Inner clearance
Healthy gap between the inner tire edge and the strut tube.
Outer / fender
Aggressive stance with higher rubbing probability — may require fender rolling or camber.
Fitment position examples
Side-profile illustrations of how the same hub looks at four common stance positions. The orange line is the hub mounting face; the dashed line is the wheel centerline.
Tucked
OEMWheel sits inboard of the fender — OEM clearance-first.
Flush
DailyOuter tire edge level with the fender lip.
Poke
StanceTire crowns past the fender — aggressive stance.
Aggressive
ShowWide wheel, low ET — often needs camber or fender rolling.
Inner clearance
SafeHealthy gap between the inner tire edge and the strut tube.
Rubbing
WarnInner tire edge contacts the strut at full compression — re-spec ET or width.
What is wheel offset?
Positive ET: mounting face sits outboard of centerline — wheel tucks inward. Most modern European cars (ET35–ET45).
Zero ET: mounting face is exactly on centerline. The wheel is symmetric around the hub.
Negative ET: mounting face sits inboard of centerline — wheel pushes outward. Trucks, classic muscle and aggressive fitments.
Read the full ET engineering guide →What is wheel poke?
Flush: outer tire edge level with fender. The visual benchmark.
Aggressive stance: tire pokes past the fender by a few millimetres or more. Often needs fender rolling or camber.
Tucked: wheel sits inboard of the fender — OEM economy and clearance-first builds.
Guide: Flush vs aggressive fitment →Backspacing vs offset
Same wheel, two reference points. Offset (ET) measures from mounting face to centerline. Backspacing measures from mounting face to inner edge.
Wider wheels gain backspacing without changing ET — which is why aggressive widths often hit the strut before the fender.
Guide: Backspacing vs offset conversion →How offset affects suspension
Offset shifts the contact patch sideways relative to the steering axis, changing scrub radius, steering effort and bump-steer.
Lower offset increases the lever arm on wheel bearings — beyond ±15 mm ET, bearing life typically halves.
Always check rubbing at full lock and full bump. Static parked clearance hides the worst case.
Guide: How offset affects handling →Common offset ranges
Typical vehicle types and stance character for popular ET values. Use as a starting reference — exact fitment varies by car.
| ET | Typical vehicle type | Stance | Poke tendency |
|---|---|---|---|
| ET45 | Compact / FWD sedan | OEM tucked | None |
| ET40 | European sedan / hatch | OEM | Minimal |
| ET35 | Sport sedan / coupe | OEM / mild flush | Slight |
| ET25 | Performance / wider aftermarket | Flush | Visible |
| ET20 | Stance / aggressive fitment | Aggressive | Noticeable |
| ET0 | Trucks, classic muscle, motorsport | Wide / centered | Significant |
| ET-12 | Off-road / heavily aggressive | Hellaflush territory | Extreme |
Popular wheel width & offset combos
Documented combinations seen on flush, OEM and aggressive builds.
| Combo | Common use | Notes | Status |
|---|---|---|---|
| 17×8 ET45 | European OEM sedan | Conservative — tucks under fender | OEM-safe |
| 18×8.5 ET35 | Most popular flush sedan setup | Daily-drivable, mild aggressive | OEM-safe |
| 18×9.5 ET22 | Wider rear / staggered sport | Flush with fender roll | Mild aggressive |
| 19×8.5 ET35 | Plus-two upgrade | Common BMW / Audi fitment | OEM-safe |
| 19×9.5 ET22 | Aggressive fitment build | Stretched tire common | Aggressive |
| 20×9 ET28 | Modern luxury / SUV | Wide OEM-style | Mild aggressive |
| 17×9 ET-6 | Truck / classic muscle | Negative ET, deep dish | Aggressive |
Popular wheel offset comparisons
Tap a comparison to load it instantly into the calculator above.
Popular vehicle offset setups
Documented OEM and aftermarket fitment patterns. Always confirm against your door-jamb placard before ordering.
BMW flush offsets
- F30 3 Series (square)18×8.5 ET35
- F30 3 Series (staggered)18×8.5 ET35 / 18×9.5 ET22
- E90 M3 OEM18×8.5 ET29 / 18×9.5 ET23
Audi OEM offsets
- B8 A4 / S418×8 ET43
- B9 RS520×9 ET26
- C7 A6 sport19×8.5 ET32
Subaru fitment offsets
- WRX STI hatch18×8.5 ET38
- Forester XT18×8 ET45
- BRZ / GR86 OEM17×7 ET48
Mustang aggressive fitment
- S550 GT square flush19×9.5 ET35
- S550 staggered aggressive19×9.5 ET20 / 19×10.5 ET10
- Foxbody classic17×9 ET0 (deep dish)
Related fitment calculators
- Wheel spacer calculator — model spacer poke and effective ET
- Tire size comparison calculator — full side-by-side fitment check
- Speedometer error calculator — diameter-driven drift
- Tire pressure calculator — adjust for size change
- Load index calculator — verify carry capacity
Wheel offset engineering guides
What Is Wheel Offset (ET)? Complete Guide
ET from first principles — positive, zero, negative.
Backspacing vs Offset: Conversion Formula
The exact formula and when each measurement is used.
Flush vs Aggressive Fitment Explained
Stance, poke and real-world daily-driving limits.
How Offset Affects Handling & Bearings
Scrub radius, bump-steer and bearing wear.