Where there’s a wheel, there could be a way toward a quick and relatively easy reduction in CO2 emissions for existing and future vehicle programs. Alcoa Wheel Products, a division of Alcoa, states that by selecting a forged alloy wheel, OEMs can see an immediate weight benefit with subsequent improvements to fuel consumption and CO2 emissions.
With "dimension creep" and pedestrian safety legislation raising hood lines, wheels have been growing proportionally larger, with subsequent increases in unsprung mass. Although cast alloy wheels can be produced cost effectively, Alcoa Wheel Products believes forging now offers an immediate weight saving solution—even on an existing vehicle platform—where traditional mass reduction programs may involve costly tooling and validation.
The company has been at the forefront of developing, producing, and supplying alloy wheels to the global automotive industry for 60 years. It now sees forging as a particularly apposite technology for current automotive needs.
Forging is the process of forcing a solid billet of aluminum between forging dies under extreme pressure. Compared to cast wheels, forging retains a better metal structure (alignment of the aluminum grain structure is retained) and offers improved strength and durability, factors that with appropriate design can lead to a significantly lighter wheel, stated Alcoa.
"Our analysis shows that an optimized forged, as opposed to cast or two-piece alloy, wheel can save up to 39 kg per car," said David Yates, Commercial and Marketing Manager, Alcoa Europe. "This is based on a 19-in U.S. SUV wheel. A recent program in Europe for a sports car manufacturer demonstrated that we could save close to 10 kg compared to their current cast wheel."
Alcoa states that a weight reduction of 45 kg (99 lb) equates to a fuel economy improvement of 1.5%.
Reducing unsprung wheel weight can improve vehicle dynamics and reduce inertia. Stated Yates: "This is a further way to improve handling or acceleration with minimal cost and testing on an existing car."
However, a forged wheel has a higher piece cost. As an aftermarket item in North America, the cost difference between forged and cast may vary from 20% to 40%, estimates Yates; but in strength terms (crush test), a forged wheel is twice as strong.
There are other benefits, he said: "A single blank can be machined into five or six variants. OEMs can quickly refresh a car or offer a range of value-added accessory products with minimal tooling. We are already offering this in the U.S. with a single blank delivering six different SUV wheels. Our eight-axis machining capability delivers a significant design and manufacturing advantage over the competition."
The Lamborghini Reventón is one of the latest cars to be equipped with Alcoa’s forged wheels. With a limited production run, Lamborghini required the flexibility of Alcoa's manufacturing capability to develop a lightweight wheel for the Reventón, which sells at 1 million euros.
Alcoa will supply the forged directional-specific 18 x 9-in front and 18 x 13-in rear wheels, with each undergoing extensive machining and finishing, resulting in lightweight construction while meeting required strength and durability. The wheels are finished in Lamborghini Bright Black and fitted with carbon fiber "winglets" to complement the Reventón’s edgy exterior surfacing.