Wheel offset (ET) decoder
What does 7.5Jx17 ET40 5x112 mean?
The rim is 7.5 inches wide (J flange) and 17 inches in diameter; ET40 means 40 mm of offset; 5x112 is the bolt pattern (5 bolts on a 112 mm circle). A smaller ET pushes the wheel further out.
- Effective offset
- ET35
- Outer face change
- +22.7 mm
- Inner clearance change
- +2.7 mm
Positive means the wheel sits farther outward, closer to the arch.
Positive means less space on the suspension/brake side.
Wheel position visual
- Current wheel:
7.5Jx17 ET45 - New wheel:
8.5Jx18 ET35 - Hub face · Effective offset: ET35 · Spacer effect: 0 mm
Before fitting, also check
- Brake caliper and barrel/spoke clearance
- Hub bore, centre rings and bolt pattern
- Bolt/stud length, seat type and torque spec
- Fender, liner and suspension clearance at full lock and compression
Positive outer change moves toward the arch; positive inner change reduces suspension/brake clearance.
Offset and backspacing tools
Backspacing estimates overall width as the marked bead-seat width plus 1 inch. Verify the manufacturer’s actual overall width.
Target-offset solver
Current wheel: 7.5Jx17 ET45
Estimate remaining measured clearance
Add your current static gaps to apply the calculated inner and outer wheel movement.
Optional: measure one or both current static gaps to estimate the nominal gap after the wheel change.
Static geometry only. Recheck tire bulge, brake spokes, steering lock and suspension compression on the vehicle.
Check centre bore and hub-ring geometry
Compare the vehicle hub diameter with the wheel centre bore using nominal measurements.
- Candidate ring size
- 72.6 → 66.6 mm
- Radial ring thickness
- 3.0 mm
Geometry only. Verify wheel design, seating, fasteners and the vehicle/wheel manufacturer instructions.
Example decoded
| Width | 7.5″ J |
|---|---|
| Diameter | 17″ |
| offset | 40 mm |
| Bolt pattern | 5×112 |
| Centre bore | 66.6 mm |
More tools
- Technical check
- 2026-07-29
- Content updated
- 2026-07-29
What changed
- Added optional measured-clearance estimates and nominal hub-bore/ring geometry without a universal fitment-success threshold.
- Added bidirectional offset/backspacing conversion and outer/inner edge target-offset solving.