Offset: Is the distance between the mounting surface of the wheel (point the wheel contacts the hub) and the center line of the wheel.
Positive Offset: Wheel touches the hub on the outer half of the wheel. The more positive offset the wheel has, the more the wheel goes inward toward the vehicle.
Negative Offset: Wheel touches the hub on the inner half of the wheel. The more negative offset the wheel has, the more the wheel goes outward away from the vehicle.
Zero Offset: Wheel touches the hub at the exact center line of the wheel.
Backspace (Backside Setting): The distance from the mounting surface to the back flange of the wheel.
Hub Centric: The wheel centers on the hub instead of the lug.
Lug Centric: The wheel centers on the lugs instead of the hub.
Caliper Clearance: The amount of space available for a brake caliper, measured from the mounting surface to the backside of the wheel center.
Centerbore: The machined opening in the center of the wheel that allows the hub to pass through.
Listed Rim Width: Measured from beadseat to beadseat inside the wheel where the tire sits.
Overall Width: Measured from outside edge to outside edge of a rim which will be 1" larger than the stated or listed rim width.
The Plus 1 guide will advise you on how to determine the tire size when going up in wheel size (ex. from a 15" to 16" wheel). Many vehicles allow a larger wheel to be installed than came originally on the vehicle. However it is critical to have the correct tire or you may experience tire rub. To "plus size" your vehicle you must choose a tire with basically the same diameter as the original. The following formula will help you determine overall tire diameter:
Step 1: Tire width (in Millimeters) X .03943 (ex. if tire size is P215/65R15 the tire width in millimeters is 215).
Step 2: Multiply your answer by the aspect ratio (ex. if tire size is P215/65R15 the aspect ratio is 65%).
Step 3: Multiply your answer by 2 and then add the rim diameter.
To plus size a vehicle with 15" rims to 16" rims when the factory tire is 205/60R15, the original diameter is 24.72 inches. Recommended plus size in 16" is 225/50R16 which has a diameter of 24.88.