Marc Christ Associate Editor
February 1, 2013

Often incorrectly referred to as rims, a wheel is the spinning component that attaches to the axle. The rim is actually one part of a wheel, the outer part containing the lip and bead for the tire. The other two parts of the wheel are the hub and the spokes. These three components work together to direct driver input to the ground through the tires. They are merely a go-between in the quest for handling, and their design can either adversely affect or favor the overall performance of the wheel, tire, and suspension combination.

For the most part, the dimensions of a wheel are determined by the dimensions of the desired tires, the dimensions of the vehicle's wheel openings, and the size and location of other suspension components (like brake calipers). But other than size, there are other factors that play a role in a wheel's anatomy. Things like composition, backspace, and offset.

Most of us understand how wheel sizes work: a 17x10-inch wheel is a 17-inch-diameter wheel with a 10-inch-wide width. That's easy to see with a simple measuring tape. But the other measurements aren't quite so simple. Offset is the distance from the wheel's hub mounting surface (flange) to the centerline of the wheel. It can be either zero, positive, or negative. Positive offset is where the hub mounting surface is farther toward the outside edge of the wheel, and negative offset is where the mounting surface is more toward the inside edge of the wheel. It is usually measured in millimeters.

Backspace, on the other hand, is the distance between the mounting face and the back inside edge of the wheel. This dictates how far in the wheel will protrude into the wheel opening from the hub. This is very important when selecting a wheel, as you don't want the lip of the wheel or the tire to scrub the inner fender or framerail. Backspace is typically measured in inches, but can also be found in millimeters.

The composition of a wheel can also play a huge role in its performance and durability. The two major types of wheels are cast and forged. Cast wheels, like most factory and affordable aftermarket wheels, are poured into a casting mold to create the wheel shape. These are very durable, and relatively inexpensive to manufacture.

Forged wheels are reserved for premium aftermarket and racing wheels. This denser, stronger product can be much lighter than its cast cousin. Less rotating weight allows for quicker acceleration and better braking. There is a cost, though, when choosing a forged wheel for your Stang. While many cast wheels can be found for a couple hundred dollars each, a set of forged wheels starts at over $2,000.

Other measurements to consider when selecting a wheel are lug pattern and hub bore. Since these don't typically change with vehicle modifications, we wont really go into that.