What is Wheel Offset? | Revv.ly Glossary

What is Offset?

I realize this is going to sound technical, but bear with me because offset is genuinely one of the most important--and most frequently misunderstood--specifications in wheel fitment. Getting it wrong can result in wheels that don't fit, handling that suffers, or clearance issues that damage suspension components. Getting it right, however, is rather satisfying.
Offset is the distance, measured in millimeters, between the wheel's mounting surface (where it bolts to the hub) and the true centerline of the wheel. That's it. But the implications of this simple measurement affect how your wheels sit relative to the fenders, suspension, and brakes.

The Three Types

Positive Offset -- The mounting surface is toward the front (street side) of the wheel's centerline. The wheel sits further inboard. Most front-wheel-drive and many modern cars use positive offset wheels, typically ranging from +35 to +50mm.
Zero Offset -- The mounting surface is exactly at the centerline. Relatively uncommon as a factory specification.
Negative Offset -- The mounting surface is toward the back (brake side) of the wheel's centerline. The wheel sits further outboard. Common on older vehicles and purpose-built for certain styles. Negative offset pushes the wheel outward, creating the "deep dish" look.

Why It Matters

Changing offset moves the wheel position relative to the car:
Lower Offset (More Negative) -- Pushes the wheel outward. Can create poke beyond the fender, may cause rubbing on suspension components or inner fenders, and changes the scrub radius (affecting steering feel and response).
Higher Offset (More Positive) -- Pulls the wheel inward. May cause contact with brake calipers or suspension parts, reduces the distance between inner wheel and these components.
The factory offset is carefully engineered to work with the suspension geometry, brake clearance, and body styling. Deviation from factory offset isn't necessarily problematic, but it requires understanding the consequences.

Calculating What Fits

Suppose your factory wheel is 8" wide with a +45mm offset. The mounting surface sits 45mm toward the front of the wheel's centerline. If you want to run a 9" wide wheel and maintain the same outer face position relative to the fender, you'd need to calculate the appropriate offset.
Width change: 9" - 8" = 1" = 25.4mm (per inch)
Half goes to each side: 12.7mm more to the outside
New offset for same outer face: +45 - 12.7 = approximately +32mm
This is a simplified calculation--actual fitment involves checking inner clearance to brakes and suspension too.

The Fitting Process

Wheel fitting is part mathematics, part trial and error:

1. Research what offsets others run on your specific vehicle
2. Consider whether fenders are rolled or modified
3. Account for tire stretch or meat if running non-standard sizes
4. Measure brake clearance if running large calipers
5. Test fit if possible before committing
   The Revvly community has extensive fitment galleries and discussions--visual proof of what combinations work on specific platforms.
   Related: Backspacing, Poke, Tuck, Hub-Centric
   Fitment-Obsessed Platforms: BMW E46, Lexus IS300, VW MK4 Golf