Wheel size is designated by rim width and rim diameter (Figure 42-2).
Rim width is determined by measuring across the rim between the flanges.
Rim diameter is measured across the bead seating areas from the top to bottom of the wheel.
Some rims have safety ridges near their lips. In the event of a tire blowout, these ridges
tend to keep the tire from moving into the dropped center and from coming off the wheel.
Replacement wheels must be equal to the original equipment wheels in load capacity, diameter, width, off-set,and
mounting configuration. An incorrect wheel can affect wheel and bearing life, ground and tire clearance,
speedometer and odometer calibrations. A wrong size wheel can also affect the antilock brake system.