📏 The Three Offsets
| Positive | Mounting surface is OUTBOARD of centerline. Wheel tucks under the fender. Common on FWD cars, most modern cars (+35 to +55mm). |
| Zero | Mounting surface IS the centerline. Less common, found on some classic and JDM applications. |
| Negative | Mounting surface is INBOARD of centerline. Wheel pokes out past the fender. Truck and deep-dish applications (−6 to −44mm). |
📐 How to Find Your Offset
- Most wheels stamp it on the back: "ET45" = +45mm offset.
- If not stamped: lay wheel face-down on a flat surface. Measure overall depth. Halve it for centerline. Measure centerline to mounting pad. That distance, positive or negative, is the offset.
- Check the OEM spec for your vehicle (door-jamb or owner's manual rarely lists it; tire-rack and wheel-fitment databases are reliable).
🔍 Why Offset Matters
Changing offset by even 10mm changes scrub radius, which alters how the car steers under braking, how loaded the wheel bearing is, and how much it rubs at full lock.
Too negative (poke) = bearing wear, rubbing on fender lips, possible illegal protrusion in some states.
Too positive (tucked too far) = rubbing on inner suspension components like struts, sway-bar end links, brake calipers.
➖ Backspacing vs Offset
Backspacing = distance from mounting face to the BACK of the wheel. Offset = distance from mounting face to the CENTER of the wheel. The two are mathematically related: BS (in) = (Width/2) + (Offset ÷ 25.4) + 0.5.
Truck wheels typically use backspacing; car wheels typically use offset.
❓ Frequently Asked Questions
What is positive offset?
Positive offset means the wheel's mounting surface is closer to the outside (street side) of the wheel. The wheel tucks under the fender. Most modern cars run +35 to +55mm.
What is negative offset?
Negative offset means the mounting surface is closer to the inside of the wheel. The wheel pokes outward past the fender. Common on lifted trucks and deep-dish wheels.
How much offset change is too much?
Generally, staying within 5mm of OEM is safest. Up to 10mm is usually fine. Beyond 10mm starts changing scrub radius significantly and may rub.
Can wrong offset damage my car?
Yes. Too far negative loads the wheel bearing improperly and accelerates wear. Too far positive can rub on suspension and brake components, causing damage.
Does offset affect handling?
Yes. More negative offset (wider track) reduces body roll and adds grip but increases steering effort and scrub radius. More positive offset does the opposite.
How do I measure offset without a wheel marking?
Place the wheel face down on a flat surface, measure the total width to get the centerline, then measure from the back of the wheel to the mounting pad. Subtract centerline depth from mounting pad depth.