Offset is the amount the rim hub is offset from center of wheel rim. Zero offset means the hub is in located in the center of the wheel rim. A negative offset means the hub is located closer to the brake side (back) of the wheel rim. A positive offset means the hub is located closer to the front side of the wheel rim.
If you use an offset differant from the original rim, the tires may scuff against the wheel well or stick out from them. A rim with more offset the original one will place additional stress on the suspension parts and cause the car to handle differantly.
I suggest you talk to a good tire dealer who knows about rims. They will understand what you are talking about and can advise you.
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