Wheel Offset & Backspace Calculator

Offset vs. Backspace

Wheel offset is the distance in millimeters from the wheel centerline to the hub mounting surface. Backspace is the distance in inches from the back edge of the wheel to the hub mounting surface. Both describe where the wheel sits relative to the hub, but they measure from different reference points. Offset is the industry standard used by wheel manufacturers, while backspace is common in the truck and off-road community.

The Formulas

Backspace = (Wheel Width / 2) + (Offset / 25.4)

Offset = (Backspace − Wheel Width / 2) × 25.4

For example, an 8"-wide wheel with +35mm offset has a backspace of (8 / 2) + (35 / 25.4) = 4.0 + 1.38 = 5.38". If you switch to a 9.5"-wide wheel and want to keep the same outer lip position, you need to increase the offset to compensate for the extra width on the inside.

Offset Types

• Positive offset (+): Hub mounting surface is toward the street side of the wheel centerline. The wheel sits further inboard. This is stock on most modern front-wheel-drive and all-wheel-drive vehicles, typically +35 to +55mm.
• Zero offset (0): Hub mounting surface is exactly at the wheel centerline. Common on classic muscle cars and some RWD trucks.
• Negative offset (−): Hub mounting surface is toward the car side of the centerline. The wheel pokes outward. Common on lifted trucks, off-road builds, and deep-dish wheels, typically −12 to −44mm.

Fitment and Clearance Concerns

Changing wheel offset moves the entire wheel and tire assembly inboard or outboard. This affects clearance in multiple areas that you need to check before committing to a new wheel:

• Fender clearance (outside): Lower offset pushes the wheel outward. If the tire lip extends past the fender, it may rub under compression or at full steering lock. Fender rolling or trimming may be required.
• Strut and suspension clearance (inside): Higher offset pulls the wheel inward, closer to the strut body, coil spring, or control arms. This is the most common interference point on lowered vehicles with aftermarket wheels.
• Brake caliper clearance: Wider wheels with deep concave faces or aggressive spokes can contact the brake caliper. Always check clearance with the wheel test-mounted before installing tires.

Scrub Radius and Handling

Offset changes also affect scrub radius — the distance between the tire contact patch center and the steering axis intersection at the ground. A large decrease in offset (moving the wheel outward) increases scrub radius, which makes the steering feel heavier, adds torque steer on front-wheel-drive cars, and increases kickback over bumps. Staying within 10-15mm of the factory offset keeps the scrub radius close to what the engineers designed the suspension geometry around.

Fitment Terms: Poke, Flush, and Tucked

• Flush: The tire sidewall or wheel lip lines up with the edge of the fender. This is the most popular fitment style for street builds because it looks clean and preserves clearance.
• Poke: The wheel and tire extend past the fender line. Common on trucks and stance builds. May require fender flares for street legality depending on your state.
• Tucked: The wheel sits inside the fender well. This is stock fitment on most vehicles and leaves the most room for suspension travel.