The major differences between forged wheels and cast wheels can be easily discerned not only by a professional engineer, but also by a knowledgeable auto enthusiast. Forged wheels provide an ‘edgy’, more expensive look and feel. Forged alloy wheels, and especially forged magnesium wheels, signify luxury and style and are often chosen as an aftermarket wheels upgrade for supercars and racing cars. But the differences go deeper than design. Forged wheels weigh around 30% lighter than cast ones. And as we’ll see, when it comes to mechanical properties, high quality forged wheels outperform cast wheels in a number of respects.
In die-casting (also called casting), metal is pre-heated until it reaches a liquid state when it is poured into a desired shape or mold. This is the most cost-effective process known today, but it has several disadvantages. When liquid metal is poured into a form it can absorb air that forms small cavities and creates a chaotic metal grain structure. Although this difference is invisible without a microscope, it negatively affects a wheel’s ability to withstand pressure. Cast wheels are more likely to crack in an accident. A test conducted by the Alcoa Technical Center (New Kensington, Pennsylvania, U.S.) simulated a truck hitting a high curb at 50 km/h. Results showed that a cast aluminum wheel broke while a forged wheel deformed, but still passed safety requirements.
During the forging process the metal remains cold and solid and is brought into the required shape by adding extremely high pressure. A true net-shape forging process requires very powerful hydraulic presses. Only a few manufacturers in the world have the equipment to utilize this technology, and SMW Engineering is one of them. Another option many famous wheel brands use today is purchasing forged wheel blanks and machining them into desired shapes.
Over time cheaper alternatives such as flow-forming and liquid forging have been developed by various other wheel producers. In flow-forming, the metal is first cast into a block with future spokes and the forerunner and then formed to the required shape by the rotary drawing method. This helps achieve a finer metal structure than during casting, but because the wheelbase is cast, the finished product remains notably heavier than a net-shape forged wheel.
Liquid forging is a hybrid of forging and casting, where molten metal is poured into a mold under high pressure. This process requires 3,000-5,000 ton presses, which are more common than 15,000+ ton presses required for near-net-shape forging. Although this helps improve wheel characteristics, liquid forged wheels lack the elasticity and ductility of true-forged ones.
A wheel made out of 2 or 3 pieces is called a component wheel. The component pieces are fastened together, with the overall wheel characteristics depending on the method used to create each of the components. Unlike forged monobloc wheels, component wheels are less durable because they are made from discrete parts attached to each other.
In a forged wheels versus cast wheels battle, forged wheels are a clear winner. High quality forged wheels are well worth the monetary investment as these light and durable wheels improve acceleration and stopping time, prolong the life of a vehicle’s suspension and contribute to lower gas mileage. That’s why a lot of today’s premium-priced cars come equipped with forged monobloc wheels or offer forged wheels as an upgrade.