Finding the right wheels requires more than selecting the brand and style you want. There are several factors that you must consider when picking a wheel set, including diameter, width, and backspace.
Wheel Width: This is the distance between the wheel's inside flanges, rounded to the nearest ½ inch. The width of the wheel must match the rim size of the tire you want to mount on it. Tires have a minimum and a maximum wheel width.
Wheel Diameter: The diameter is the distance from bead seat to bead seat across the center of the wheel. The wheel diameter must be the same as the tire rim diameter. Verify that the wheel diameter stamped on the wheel and the tire.
Wheel Offset: The offset is the distance between the hub of the drum and the centerline rim of the wheel mounting surface. The offset provides a vehicle's "track," which is the distance between tires on each axle. Keep wheel offsets as close to factory as possible. This will allow you to avoid steering problems.
Wheel without tire
The most effective way to measure the backspace of a wheel is to lay it face-down, with the backside of the wheel facing up. Lay a straight edge diagonally across the inboard flange of the wheel, then measure the distance from the point that the straight edge contacts the flange to the hub mounting pad of the wheel with a tape measure. The result is the backspace of the wheel.