If the rear wheels are 18", they are not factory wheels.
Before anyone can answer your question, you would need to provide additional information, such as:
- make and style of wheels (photo or link would be helpful)
- size of the wheels, including width
- description of the wheel condition, including any flaws such as gouges, chips, scratches, curbing, etc (photo would be helpful)
- make, model, and size of the tires
- description of the tire condition, including a tread depth measurement (in 32nds of an inch)