Fitment Lab
Offset, width and tire size: see poke, inset and clearance before you buy.
MEASURED GAPS optional: turns the difference into room left
On the current setup, wheels straight, car on the ground: measure from the outermost point of the tire or lip straight out to the fender edge (a plumb line helps), and from the innermost point of the tire or wheel to the nearest part of the strut or spring perch.
The new setup sticks out 23.8 mm more and gives 2.2 mm more room inside.
Poke (outside)+23.8mmtoward the fender
Inside (strut side)−2.2mmmore room
| CURRENT | NEW | CHANGE | |
|---|---|---|---|
| Effective offset | ET35 | ET22 | |
| Backspacing | 6.13″ | 6.12″ | |
| Hub face to outer lip | 85.6 mm | 111.3 mm | +25.7 |
| Hub face to inner lip | 155.6 mm | 155.3 mm | −0.3 |
| Tire diameter | 653.2 mm (25.7″) | 635.7 mm (25.0″) | −17.5 mm |
| Sidewall | 98.0 mm | 89.3 mm | |
| Tire width | 245 mm | 255 mm | |
| Revs per mile | 784 | 806 | |
| Tire on this wheel | in range (typ. 8–9.5″) | in range (typ. 8.5–9.5″) | |
| Speedo reads 60 | 60 | 58.4 actual | −2.68% |
KNOW THE TERMS
- Offset (ET)
- Distance in mm from the wheel's centreline to the face that bolts to the hub. Higher offset pulls the wheel in; lower (or negative) pushes it out.
- Poke
- How far the wheel and tire stick out toward the fender. Here it's measured at the outermost point, lip or tire, whichever is further out.
- Inside / inset
- How far the wheel and tire reach in toward the strut, spring perch and brake caliper.
- Backspacing
- Distance from the hub face to the inner edge of the wheel, in inches, including the flange. Same information as offset, used mostly in the US.
- Spacer
- A plate between hub and wheel. It moves everything out by its thickness, the same as lowering the offset by that much.
- 245/40R18
- Tire section width in mm / sidewall height as a % of the width / radial construction, then the wheel diameter in inches.
- Stretched / bulged
- A tire on a wheel wider than its typical range is stretched; narrower, the sidewall bulges. The tire maker's approved rim list is the real authority.
- Speedo error
- A taller tire covers more ground per turn, so you're going faster than the speedo says; a shorter one, slower.
ASSUMPTIONS
- Wheel lips are nominal width plus the standard ½″ flange each side; real lips vary a few mm by design.
- Tire width is the section width from the size. Actual width changes about 5 mm per ½″ of rim width and varies by brand.
- The tire is centred on the wheel. Wheels straight, car at rest: no suspension travel, camber change or steering lock.
- Measured gaps are taken from the current setup's outermost and innermost points, straight across.
- Brake caliper and spoke clearance aren't covered: those depend on the wheel's spoke design, not just its offset.