# Wheel Anatomy 201: Beads and Flanges

Welcome, students, to Wheel Anatomy 201: Beads and Flanges. Today we will be reviewing the various structures located on the outer barrel of the wheel. These structures will include the drop center, beads, mounting humps and flanges. Please be sure that you have your wheel diagram available to refer to as we proceed. As always, you may find it easier to right-click on the link and open the diagram in a new tab.

## Barrel

The part of the wheel between the outboard face and inboard rim edge is called the barrel. The barrel is shaped to create the tire mounting structures such as the drop center and the flanges. When the tire is mounted, the outer surface of the barrel closes off the open end of the tire, enabling the tire to hold pressure.

## Drop Center

Most wheels will have a portion of the barrel that is bent inward, creating a ringlike area around the barrel that is closer to the centerline of the wheel than the rest of the barrel. In order to mount a tire that has the same inner diameter as the wheel's outer diameter, one side of the tire must be placed into this depression on the wheel so that the tire can “slide over” just enough to let the other side of the tire slip over the rim edge. This “drop center” will be closer to one or the other edge of the wheel. When the drop center is closer to the face of the wheel, it is known as a “front-mount” wheel and can be placed on a tire mounter with the face up. The tire is then mounted over the outer face of the wheel. On many “deep-dish” wheels, however, it is not possible to place the drop center near the front face because of the dish, and so the drop center is placed closer to the inboard edge of the wheel. These wheels are known as “reverse-mount”, and must be carefully clamped onto the mounter with the face down.

## Flanges

What we call flanges are the flared edges of the barrel on both the inboard and outboard sides of the wheel. The metal of the barrel is flared 90 degrees outward on each side. This prevents the tire from slipping off the wheel. Of course, the outer edge of the outboard flange is also part of the cosmetic face of the wheel.