Offsets:
Another important dimension to be considered when looking for wheels is offset. Offset is the distance from the mounting face of the wheel spider to the rim centerline. Offset is positive when the mounting face (lug circle) is outboard of the centerline and negative if the lug circle is inboard of the centerline. All wheels are designed for either positive, negative or zero offset, usually for disc brake clearance or for handling characteristics.
You generally want to stay at the same offset as your stock wheel.
Generally, you should not increase the offset more than 1/2 inch (12mm) or tire width by 1 inch (25mm), or you'll create further problems. Increasing offset 1/2 inch (12mm) or tire width 1 inch (25mm) will put the entire extra tire width 1/2 inch (12mm) to the outside, where it may not clear the wheel well. Increasing the offset also has the effect of loading the front wheel bearings past their design limits and can actually "cock" the bearings causing rapid wear or premature failure.
Occasionally, disc brakes cause a mounting problem; some wheels were not designed for use with disc brakes and will not clear the brake caliper or will interfere with the disc. Be sure to check before buying wheels, especially used wheels, that they will fit your vehicle. Be sure that the tires on wider wheels will clear the wheel wells, especially when turned at full lock, and that the tires do not interfere with suspension travel.
1. When changing diameters and offset, your number one concern is to make sure the wheel will fit with your current suspension and bodywork. Every car is different, so check with other people who have your same car to determine what will fit with your brakes, suspension drop, body work, etc.
2. When going to a smaller offset wheel, toe-in must be increased (same as decreasing toe-out) to compensate.
3. Different offset will cause the same wheel to weigh more or less. The general rule is that the lower the offset (less positive), the higher the weight because the hub face is thicker.
Sources: AutoZone
The Centerbore & Hub-Centric Wheels:
The centerbore of a wheel is the machined opening on the back of the wheel that centers the wheel properly on the hub of a vehicle. This hole is machined to exactly match the hub so the wheels are precisely positioned as the lug hardware is torqued down. Keeping the wheel precisely centered on the hub when it is mounted will minimize the chance of a vibration. Some wheels are vehicle model specific and will come from the factory with a bore machined to match that vehicle. Some wheels are designed to fit multiple vehicle models and will use a centering ring system to reduce the bore size to match the hubs of different vehicles. These rings keep the wheel precisely positioned as the lug hardware is torqued down.
Some wheels are non-hubcentric by design. These are known as lug-centric wheels. With these wheels it is critical to torque the lug hardware with the vehicle on jack stands, off the ground. This allows the nuts or bolts to center the wheel and torque down without the weight of the vehicle pushing them off center.
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