Wheel adapters have three main functions.
Change bolt patterns and properly fit wheels from one vehicle to the hub of a different vehicle.
Adapt aftermarket or stock wheels to a trailer.
Modify a wheel bolt pattern and install wheels that may have a different bolt pattern.
Wheel spacers can widen the stance on the cars, trucks and SUVs. Spacers are often used to fix back spacing and clearance issues. Most wheel spacers are designed to bolt between a wheel and the stock mounting hub to match up the stance of the vehicle.