Forged Wheels Move Into the Volume Market

When it comes to alloy wheels, there is no doubt that forged products are top of the tree in terms of strength, technological benefits but also price. However, while they will never be the cheapest products on offer, there are signs that their fitment is becoming increasingly prevalent in the marketplace, with some of the best known volume models now sporting forged aluminium wheels as an option. Tyres & Accessories interviewed David Yates, marketing manager for Alcoa Forged Specialty Wheels, Europe to find out more.

You might think that the recession would have put the kibosh on sales of what is to all extents and purposes the premium of wheel upgrade options. However, while the environment has been tough for everyone, things have not been as bad as could have been expected for Alcoa forged wheel. In fact, according to David Yates, when you consider the US-based company’s relatively short history of selling forged wheels in the European market, there is a lot to be pleased about: “The credit crunch has had an affect on us. Car wheel volumes have been reduced significantly overall, however these are growing “rapidly” in Europe. Although we [Alcoa] invented forged wheels 60 years ago, we have only been pushing passenger car forged wheels in Europe for less than 3.5 years, following the US model [of introduction].”

What has changed since the last time Tyres &Accessories spoke to Alcoa on this subject is that forged wheels have moved from only being supplied on the supersport cars, to luxury brands last year and, most recently, into the realm of true volume production. While cars like the Toyota Prius and its Hybrid drive have been designed with fuel consumption in mind for a fairly long time, others haven’t, and still more want to work in further reductions and benefits and so require the benefits offered by lighter, stronger wheels such as forged products.

Before the credit crunch Alcoa was knocking on the door of selling 2 million units a year in Europe. Last year saw this figure “reduce a little bit,” but 2010 is already showing signs of recovery with “OEMs we never thought would look at our wheels” taking an interest. Take a look close look at the Vauxhall/Opel Insignia OPC, for example. The high performance variant of the 2009 UK car of the year comes with 19-inch wheels (on 245/40), but crucially offers 20-inch lightweight forged wheels (with 255/35 tyres) as an option. Peugeot/PSA models are expected to do something similar next, with the best known German and American volume brands also said to be taking an interest. In the longer term company forecasts are aiming to quadruple this by around 2015.

Alcoa aiming to sell 8 million a year by 2015

The key to Alcoa Europe’s recent development has been its relationships with purchasing OEMs. And the current legislative and economic climate has provided a particularly good opportunity to present the benefits of forged technology – tough emissions targets of 130 g/km of CO2 are increasingly forcing carmakers to find additional methods of reduced fuel consumption. The European rules, passed in December 2008, mean a new CO2 regulation was agreed for the continent, with a target emission level of 130g/km per vehicle. This is being phased in over the coming years, but by 2012 75 per cent of each car manufacturer’s new registrations have to comply with the level or face punitive fines.

With the weight saving possible, stylists no longer have to feel guilty about selecting large wheels as forging minimises the engineering compromises,” claims Yates, adding: “Reducing the unsprung wheel weight can improve vehicle dynamics while reducing wheel and tyre inertia improves fuel economy. Our analysis shows an optimised forged, as opposed to cast or two-piece alloy wheel, can actually save up to 39kg per car.” This is based on a 19-inch US SUV wheel, but a recent Alcoa programme for a European sports car manufacturer demonstrated a saving of 12kg per vehicle over their current cast wheel. “A good rule of thumb is that every 30kg saved equates to a fuel economy improvement of one per cent,” says Yates.

One of the key benefits of taking to the forged approach is that a phenomenon called “rotational inertia” has an exponential effect when it comes to reducing fuel consumption. This effect, which for those most familiar with tyres, can be helpfully compared to rolling resistance, which has a similarly positive effect to low rolling resistance tyres, meaning the benefits of lower weight wheel increase as the weight reduction increases. The concept rests on the specifics of where the wheel is heaviest.

There has always been an effort to manage wheel weight with respect to predetermined targets provided by the automotive OEMs. The benefits of reducing un-sprung weight and the corresponding positive effect on noise, vibration, and performance are well known. However, there has been comparatively little effort in managing the distribution of mass within the wheel. As the vehicle moves (translational or linear movement), the wheel and tyre combination moves with it. In addition, the wheel and tyre rotate. Forces are required to accelerate the wheel and tyre in both a linear and a rotational direction. To minimise the rotational force required for a given wheel mass, the rotational inertia should be at a minimum. Consequently, every gram saved at the rim is more useful than a gram saved at the hub. Alcoa’s engineers have exploited the strength properties associated forged aluminium (such is the benefit from alignment of the aluminium grain structure, Alcoa reports forged wheels can offer double the strength of a cast wheel in a 20 per cent lighter finished product) to produce the lightest practical rims.

The benefit can be magnified by the use of lower aspect tyres which weigh less than their taller predecessors. A forged wheel makes a bigger rim diameter feasible as a replacement for a given cast wheel diameter. By maintaining the original outer tyre diameter, a saving in tyre mass is achieved. The strength of a forged wheel also allows vehicle designers increased flexibility with other parts of the car. For example, designers push for the spoke/rim interface to be as tight as possible while engineers seek to accommodate bigger and bigger disc and caliper packages within the wheel. The casting process inhibits this; radii and fillets have to be introduced and draft angles allowed for.

The design flexibility from forging also helps vehicle manufacturers offer multiple wheel variants from a single blank. “Several different designs can be machined up from a single blank,” says Yates. “OEMs can quickly refresh a car or offer a range of value-added accessory products with minimal tooling. We are already doing this in the US with a single blank providing six different SUV wheels.” To achieve this flexibility, Alcoa Wheel Products has invested in the latest machinery, as Yates keenly points out: “Our eight-axis machining capability delivers a significant design and manufacturing advantage over the competition.”

As increasing manufacturing volumes enable Alcoa’s premium forged wheels to compete more closely with cheaper cast wheels, the prospects look good for wider adoption of forged wheels across the mainstream vehicle population. Ongoing developments in technology are leading to ever lighter wheels and OEMs seeking reductions in fuel consumption are keen to take advantage of ‘bolt-on’ benefits, requiring only minimal type approval.

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