A lot of measurements need to be taken to make sure a given wheel is going to properly fit a given car. This graphic provided by Larry Kingsland of Boze Alloys shows a few of them. Inner Measurement (A) is the hub face to the inner wheelwell. Knowing this will make sure your tire doesn’t rub on the inside. The Outer Measurement (B) determines the clearance to the outer lip. The Brake Caliper (C) and Brake Radius (D) measurements help ensure that the caliper clears the wheel hoop as well as the spokes. This is especially critical when running big-brake kits. Hub diameter (E) and Hub Height (F) is important as well. If the hub is too big, then the wheel won’t fit on the car; too small and the wheel won’t be properly centered, or “hub centric,” and instead you’ll have to hope that the lugs properly center the wheel.