Backspacing – isalso called rear spacing, it is the distance from the mounting pad to the back edge of the rim. This is different than wheel offset.
Bolt Pattern – is the arrangement of the bolt holes on a wheel. The bolt pattern or bolt circle is the diameter of an imaginary circle (P.C.D) formed by the centers of the wheel lugs. Most bolt patterns are represented in the following manner: 100 x 4H or 4/100. The "100" indicates the diameter of the bolt circle measured in millimeters. The “4” indicates the number of lug holes. Bolt patterns can be 4, 5, 6, 8, or 10 lug holes. However, tuner applications are typically 4 or 5 lugs. Bolt patterns are measured in both inches and millimeters. Thus, a wheel with 5 lug holes and a diameter of 114.3 mm can be referred to as either 5 x 114.3 or 5 x 4.5. 1 inch is equivalent to 25.4 mm.
Cast Wheels – is the most common type of aluminum wheel. Casting is a relatively inexpensive way to produce quality alloy wheels. The casting of wheels is the process of getting molten aluminum inside a mold to form a wheel. There are two methods used to produce cast wheels, gravity casting and low pressure casting.
Casting, Gravity – is the process of pouring molten aluminum into a mold utilizing the earth’s gravity to fill the mold while it cooled. Gravity casting is one of the most economical methods to manufacture alloy wheels if reducing weight is not a primary concern. Since the process relies on the earth’s gravity to fill the mold, the aluminum is not as densely packed in the mold as the low pressure casting. Generally speaking, gravity cast wheels will have to be made heavier in order to achieve the desired strength.
Casting, Low Pressure– isthe process of the molten aluminum drawn up into the mold using a high-pressure vacuum. Low pressure casting allows the molten aluminum to move quicker into the mold thus produces a finished product that is denser with less trapped air than gravity cast wheels. Although low pressure cast wheels are stronger and less porous than gravity cast wheels, the production cost is significantly higher.
Center bore – is the size of the machined hole on the back of the wheel that centers it properly on the hub of the car. Center bores are measured in inches or mm. When the wheel is perfectly positioned with its center bore matching the hub or becomes hub centric, the chance of vibration is minimized. Sometimes hub rings may be required to be placed in the back of the wheels for them to become hub centric and thus reduce the risk of vibration while driving.
Forged Wheels, Fully– is c onsidered the best wheel manufacturing technique. Forging allows for the compression of an aluminum billet (one solid piece of aluminum) into an aluminum wheel using over 8000 tons or 16 million pounds of pressure combined with heat. Forging produces a wheel that is both stronger and lighter then the standard low pressure aluminum wheel. The costs of tooling, technology, development and equipment make this type of wheel very exclusive and usually demand a high price in the aftermarket.
Forged Wheels, Semi-Solid – is a process which the aluminum billet is heated to an almost liquid state and then it is forced into a mold at a very high rate. The finished product offers mechanical properties very similar to the fully forged wheel but without its high production and tooling costs. Although semi-solid wheel may offer an excellent value to many consumers, fully forged wheel remains the ultimate wheel in the market.
Hub Centric – is a wheel with a center bore made to match up with a vehicle's hub diameter.
Hub Centric Rings (Hub Rings or Spacers) – is the hard plastic or aluminum rings mounted on a vehicle's hub before the wheel. Without hub rings, there is a possibility of getting a vibration even if the wheel & tire assembly is perfectly balanced.
Load Index – indicates the maximum weight that each tire is able to support.