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Wheel Anatomy: Part II

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Last month, we began a multi-part series on the concepting, design and production of today’s hot custom wheels with an inside look at cast one-piece aluminum wheels. This month, we’re going to touch on the newest forged one-piece wheels and then describe two-piece wheels.

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Forged wheels are literally forged in a press and made into one-, two- and three-piece wheels.

With one-piece cast wheels being shifted more and more to Pacific rim countries, forged wheels are becoming the hot ticket in the U.S. for manufacturers that want to keep or gain marketshare. The biggest advantages of a forged wheel are its strength, lighter weight and outstanding surface finish.

Some forged wheels are made in a press, but there are other, newer processes that actually use a forging press to spin a die while pressing an aluminum billet into shape. This process – rotary forging – causes the molecular structure of the wheel to line up in such a way that it becomes even stronger than a traditional forged wheel. Advanced Metalforming Technologies in Oxnard, Calif., uses such equipment.

Depending on the process, billet aluminum can be pressed to a near net shape that requires 20% less finish machining, or it can be pressed into a flat disc with various profiles that can be used to create different designs when milled out. Here, you see a disc being spun into what will eventually be a one-piece forged wheel.

This process produces a raw spun wheel ready to be CNC-machined into the desired design. A lack of seams afforded by forging allows these wheels to be easily painted, polished or chrome plated.

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The design of the wheel is created with CAD/CAM software, which produces a 2D and 3D model of the wheel.

After machining, the finished wheel looks exactly like the computer model.

But, as is the case with cast aluminum wheels, the variety of widths and offsets possible with one-piece forged wheels are limited.

Two-Piece Wheels

Traditionally, two-piece aluminum wheels have an outer rim, known as a “hoop,” that is created by taking a straight, flat piece of aluminum and rolling it into a circle. The seam joining the ends is welded, and the hoop is placed onto a machine that presses a roller against the hoop to form the contour of the flanges, bead seats, bell and drop center.

Cast, billet or forged centers can be used to complete a two-piece aluminum wheel. The centers are pressed into the outer hoop using a process known as “sweating,” in which the outer hoop is heated, causing it to expand. The face is then pressed into the outer hoop at a specified backside setting and then welded into place.

The biggest benefit of a two-piece wheel over a one-piece is the variety of offsets and widths possible. That’s because the centers can be placed virtually anywhere within the hoop. Typically, a two-piece wheel is lighter than a comparably sized one-piece unit, which contributes to better handling and improved gas mileage.

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The lighter weight also helps in racing applications because the lighter the wheel, the less torque it takes to turn it. This translates into lower unsprung weight and quicker ETs at the drag strip. We’ll cover this topic more in-depth in an upcoming article. For now, you can see how this new forging technology is creating spectacular two-piece wheels like never before.

Advanced Metalforming Technologies has the ability to create a forged outer hoop, the benefit of which is added strength, especially in the flanges. Rolled outer hoops don’t hold up well to curb damage or potholes, but a forged one has the strength to go rock climbing yet still offer the flexibility of custom widths and offsets.

One word of caution, though, concerning a two-piece wheel: These days, the popular use of an outer hoop is to flip it around and place the drop center toward the rear. This allows the designer to create a face that is larger, thus providing the illusion of a larger wheel. The drawback, however, is that this places the narrow part of the drop center where the brake caliper should be located.

When Dodge started putting 17-inch wheels on trucks as OE, they also beefed up the calipers. The first time we all started putting new 17-inch wheels on the truck, it wasn’t clear if the drop center was reversed unless we went to 18 inches or larger. So, make sure your technicians conduct a complete dry test fit before mounting tires on these wheels.

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Also, it’s critical that your employees mount these tires from the rear on a reversed drop center wheel while clamping it from the outside.

Obviously, the price of new wheels has to reflect all of these advances in technology and production. So, next time you see a two-piece wheel at double the price of a one-piece, you’ll know why.

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