How far the mounting surface is from the centerline. High offset: Tucks wheels into the fender. Low offset: Pushes wheels out for a "wide" look.
High shine, but requires constant cleaning and can peel over time.
A hybrid process. Lighter and stronger than standard casting.
If you buy larger rims, you must buy tires with a lower profile (shorter sidewall). This ensures your stays accurate and your tires don't rub against the wheel wells.
