Some info that i got from internet...
The most important step in choosing your rims is in the specifications. It is crucial to proper operation and performance that the rims fit your ride properly. These specs include the rim diameter, width, bolt pattern, and offset. The rim diameter is the size of the rim measured across its center. Most enthusiasts look for something that's a couple of inches bigger than the factory diameter to help "fill in" the space in the rim well. The width refers to the distance from the inner lip to the outer lip of the rim as viewed from the top. Original equipment rims are typically a bit too narrow to achieve optimal performance results. A slightly wider rim gives you the ability to install a wider tire, increasing the amount of tread on the pavement and improving traction and cornering performance. The bolt pattern specifies the configuration of lug holes both in total number (4-bolt / 5-bolt / 6-bolt), and the distance between them across the center of the rim. For instance, a rim with a 4:100 bolt pattern has 4 lug holes spaced 100mm apart when measured from the center of the rim. Auto manufacturers use several different arrangements depending the make and model. The offset is the measured distance between the rims mounting surface on the hub, and the centerline of the rim. It's responsible for the fitment of the rim in the wheel well from side to side. It's critical, especially on lowered vehicles, that the offset is correct for the application to keep the tires from rubbing on the edge of the fenders when the suspension travels downward. It is measured in high (positive), medium (zero), and low (negative) ratings.
The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types.
The hub mounting surface is even with the centerline of the wheel.
The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.
The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.
If the offset of the wheel is not correct for the car, the handling can be adversely affected. When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. For most cars, this won't work correctly. We have test fitted thousands of different vehicles for proper fitment. Our extensive database allows our sales staff to offer you the perfect fit for your vehicle.