Compare your current and new wheel setup to calculate inner clearance, outer wheel position, effective offset, backspacing, and the effect of wheel spacers.
Wheel width is converted from inches to millimeters before calculating its inner and outer positions. One inch equals 25.4 millimeters.
Consider replacing an 8-inch-wide ET35 wheel with a 9-inch-wide ET30 wheel without using a spacer.
The new wheel provides approximately 17.7 mm less inner clearance and extends approximately 30.4 mm farther outward.
A positive offset places more of the wheel inward toward the suspension and vehicle body.
Zero offset means the hub mounting surface is positioned directly on the wheel centerline.
A negative offset moves the wheel farther outward and can create a deeper wheel appearance.
Inner clearance is the available space between the wheel and suspension or brake components.
Outer position indicates how far the wheel moves toward the fender compared with the old setup.
A spacer reduces the effective offset and moves the entire wheel outward by its thickness.
Wheel offset is the distance between the wheel centerline and the surface that mounts against the vehicle hub. It is normally measured in millimeters.
ET is an abbreviation used for wheel offset. For example, ET35 means the wheel has a positive offset of 35 millimeters.
Less inner clearance means the new wheel sits closer to suspension, brake, or body components. Physical clearance should be checked before installation.
Farther outward means the outside edge of the new wheel moves closer to the fender or extends farther beyond the body compared with the old wheel.
A spacer reduces the effective positive offset. For example, an ET40 wheel with a 10 mm spacer has an effective offset of ET30.
No. Offset measures the mounting surface relative to the wheel centerline, while backspacing measures the distance from the mounting surface to the inner edge of the wheel.
A lower offset moves the wheel outward and may cause the tire or wheel to contact the fender. Wheel width, tire size, suspension height, and steering movement also affect rubbing.
This calculator compares wheel width and offset. Tire width, sidewall shape, suspension travel, camber, and vehicle ride height must also be checked separately.