Cast VS. Rotary Forged VS. Fully Forged Wheels: What's the difference?
Not all wheels are created equal. If you're looking for aftermarket wheels, there are several things that you should consider. As wheels are made using different methods and alloys, they have distinct advantages and disadvantages over one another. Some wheels are inexpensive to purchase, some offer premium quality, and some focus on style solely.
If you're looking for aftermarket wheels, there are several things that you should consider. As wheels are made using different methods and alloys, they have distinct advantages and disadvantages over one another. Some wheels are inexpensive to purchase, some offer premium quality, and some focus on style solely. Modern car wheels are getting more durable and aesthetically pleasing as technology and manufacturing improvements. As we continue our discussion of wheels, we'll take a peek at the difference between cast wheels, Flow Form wheels, and forged wheels.
What are cast wheels?
The most common type of aftermarket wheels is cast wheels. They are made by pouring molten aluminum into a mold to form the shape by either gravity or low pressure. Cast wheels are the most common type of wheels that account for 90% of OE (Originally Equipped) wheels that are found on most cars. There are two popular casting methods used by manufacturers: gravity casting and low-pressure casting.
Gravity Casting: Gravity casting involves utilizing the earth's gravity to fill the mold with molten aluminum. This method is a cost-effective solution for producing a large number of identical wheels in a short amount of time. The process solely relies on gravity to do the work, where the aluminum molecules are not as densely packed in the mold as the other methods would offer. To compensate for the fact there may be voids formed during the cooling process, gravity-cast wheels often use extra material on the design to account for porosity thus making the wheels heavier with bulkier spokes.
Low-pressure casting: Low-pressure casting is the most popular casting method used by manufacturers nowadays. It involves injecting molten aluminum quickly into the mold by applying positive pressure. It results in a denser and more consistent wheel with better mechanical properties than a gravity-cast wheel. This method has a slightly higher production cost than gravity casting but offers higher quality.
What are Rotary Forged wheels?
It has many different names from different manufacturers: FlowForm, Rotary Forged, Flow Forged, Hybrid Forged, etc. Rotary forged wheels combine the manufacturing techniques of both casting and forging. It begins with low-pressure casting to form the wheel face with a shortened and thickened barrel on the backside. Then a rotary machine will spin, heat up and use rollers to press the thickened part of the barrel into its final width and shape. Through a combination of heat, pressure, and spinning, the process aligns the grain structure and molecular properties of the aluminum alloy, resulting in greater strength on the barrel of the wheel. This hybrid manufacturing technique creates the wheel with a cast spoke face and a forged-like barrel. Many manufacturers now have a Rotary Forged wheels lineup available as an intermediate option bridging the gap between cast and fully forged wheels. Rotary Forged wheels are suitable for most drivers who are looking to enhance the look and performance of their car at a lower price point.
What are forged wheels?
Forged wheels are the pinnacle in aftermarket wheels.
Forged wheels typically use aerospace-grade 6061-T6 forged aluminum alloys as raw material which has the best mechanical property for engineers to work with. To manufacture this raw material, a large piece of an aluminum cylinder is heated up under controlled high temperature, then put into a hydraulic press and pressed into a much smaller block under 8,000 to 10,000 tons of pressure. The resulting part is commonly called “forging”. These forgings are shipped to manufacturers where wheel designs will be shaped using CNC (Computer Numerically Controlled) machines. The forgings will go through a series of CNC operations to create the profile, width, offset, and spokes. Then finishes are applied by hand to create the finished wheel.
This manufacturing process eliminates any porosity, shrinkage, and other micro-processes presented in the raw material. The resulting aluminum material has a high degree of uniformity in the grain structure which allows the material to have a very high strength-to-weight ratio. As a result, forged wheels can be much more durable with much less material resulting in a far lighter wheel than rotary forged and cast wheels.
Off the shelf VS Custom Forged Wheels
Some manufacturers offer off-the-shelf forged wheels, these forged wheels are mass-produced with pre-made sizes, widths, offsets, bolt patterns, and a limited selection of finishes to choose from. An advantage of this method is that the wheels are immediately ready to ship. Custom forged wheels usually take between 4-7 weeks to manufacture.
Forgelite’s custom forged wheels are individually made to order, and there's a wide array of customization options such as diameter, width, offset, and brake clearance. Additionally, Forgelite offers over 42 curated powder coat finish options to choose from (with access to 6500+ powder coats from Prismatic Powders), and custom-milled engraving on your wheels.
Another advantage of custom forged wheels is the ability to maximize concavity. Since each set is tailor-made to the client’s vehicle, You can virtually customize every aspect of the wheel to make them fit your style. The costs of material, labor, tooling, development and manufacturing processes make forged wheels very exclusive and come at a premium price point. If you want the best in aftermarket wheels, forged wheels are for you.
Wheel weight is the most popular topic when discussing aftermarket wheels. The mass of the wheels contributes to the unsprung weight of a car. Unsprung weight refers to weight below the vehicle suspension including wheel, tires, and brakes. As the unsprung weight can heavily affect how the vehicle feels and handles. The lighter the unsprung weight, the better the car handles. Weight reduction is the main goal of performance wheels.
Aftermarket cast wheels are sometimes lighter than OE wheels depending on the styles and sizes. However, to combat the material irregularity in casting aluminum, manufacturers have to add redundant material to spokes and barrels to increase their strength, thus making the wheel heavy.
Rotary Forged is lighter compared to cast wheels. The face/spokes are the same as a cast wheel, while the barrel is rolled out with heat and pressure. Therefore the barrel poses a forged-like strength which in return reduces its thickness and reduces overall wheel weight.
A fully forged wheel is the lightest among them all, it’s generally 25-30% lighter compared to a cast wheel of the same size. The forged 6061-T6 aluminum has outstanding mechanical strength, manufacturers can use a lot less material to achieve the same strength compared to cast or Rotary Forged wheels. Therefore forged wheels have slimmer spoke designs and have weight-reduction pockets cut into the back, which further reduces their weight.
Regardless of what type of manufacturing methods are used to make wheels, all wheels need to undergo physical or computer simulation tests to make sure they meet all applicable regulations and safety standards. However, the difference in material shows if there is an impact on the wheel. Under heavy impact, cast wheels tend to crack and break due to voids presented in the casting aluminum. In most situations, it would be fine, but if the wheel snapped, the result can be catastrophic. So when buying cast wheels, it is always recommended to choose a reputable brand because of safety concerns. Rotary wheel barrels are stronger than cast wheels, however, due to the spokes being the same as cast wheels, a similar cracking and breaking situation would happen under heavy impact. Fully forged wheels are the strongest in theory, however, because manufacturers use less material to achieve the same strength as all others, it will take the same amount of force and loading. The difference is that under the impact, the forged aluminum will bend out of shape instead of snapping to allow for sufficient time for the driver to stop the car safely.
The performance of the wheel affects how a car handles and feels, and it is largely due to the weight of the wheels like mentioned before. “Unsprung Weight/Mass” commonly refers to the weight of all car parts that are below suspensions such as brakes, wheels, and tires. It affects how quickly a car can turn, accelerate and turn. Therefore, a low unsprung weight will improve a vehicle’s handling and performance. Forged wheels being the lightest of them all brings the driver the most significant improvement, followed by rotary-formed wheels, then cast wheels. In addition, because of the material strength and rigidity used to produce forged wheels, they provide better lateral support to the vehicle when taking corners at high speeds, as well as providing excellent feedback from the road surface.
Because the casting process involves a casting and a de-molding process, to produce parts without defects, many manufacturers choose simplified designs to make sure molten aluminum can reach every corner of the mold and can be easily taken out of the mold after cooling down. As a result, cast wheels are often plain and rounded on the design with a painted finish to cover any surface imperfection. Rotary-formed wheels are similar to cast wheels, however often they go through a simple machining process to add additional features and elements. Forged wheels often have complex designs thanks to modern precision machining techniques. Starting from a solid chunk of forging, a high-precision CNC machine is capable of carving out the smallest surface detail that the designer envisioned. With hand-applied premium finishes such as brushed or polished finish. Forged wheels are often considered a precision art piece that can greatly accentuate a car.
Cast wheels are the least expensive among all due to their simple design and mass production capability. They are popular among all levels of car enthusiasts due to their availability and affordability. Rotary-formed wheels typically cost more than cast wheels due to a more complex manufacturing method. However, they are still typically about a quarter of the price of fully forged wheels. Therefore it has gained big popularity in recent years as they are relatively inexpensive and also much lighter compared to cast wheels. Forged wheels are the real premium products. A set of forged wheels are typically in the price range of thousands of dollars due to the labor, material, and equipment involved in the manufacturing process. However, it offers the most custom wheel experience as almost every set of wheels is individually made so they can be tailored to your car.
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