MUNICH: You can't re-invent the car wheel, but that hasn't stopped it from evolving considerably over the past few decades. Car wheels have become increasingly sophisticated design elements and they are still changing.
Thanks to the recent focus on efficiency, particularly among electric cars, more attention than ever is being paid to wheel designs, leading to disc-like rims that reduce drag.
Most wheels are silver or black and brightly-coloured wheels are the exception. Soon it may be possible to change the colour on demand. BMW recently presented a chameleon-like, colour-changing version on its i Vision Dee study. The wheels are covered with a special foil from the supplier E Ink.
The colour of the foil changes using an electrical impulse and up to 32 colours are possible.
"This results in different colour combinations so that the car and also the wheels can appear in a different colour or pattern depending on the driver's wishes or the purpose of use," says Stella Clarke who is E Ink project manager at BMW.
After the electrical impulse has been given, the power is switched off and the wheel colour "freezes". The hue is retained in a power-saving manner, says the carmaker,
Although there are currently no plans to use the technology in series production, BMW claims this is possible. Especially if it proves feasible to paint the e-ink film directly onto the body and wheels instead of a foil. This would be faster and cheaper in production than gluing.
Whereas in the 1980s wheels of 15 or 16 inches were considered large, today's cars often use wheels sized between 19 and 23 inches. This not only makes cars look more imposing but helps accommodate the larger brake systems of increasingly powerful models.
"For decades, car wheels were considered a functional element. Above all, they were supposed to be robust," says Paolo Tumminelli, design professor at Cologne Technical University.
Tumminelli also sees a trend in manufacturers designing wheels to fit a specific model. "There are only a few uniform wheels for all vehicles now, because the wheels have to harmonise with the vehicle's design," says Tumminelli.
"The wheel must literally and visually carry the vehicle and contribute to an overall harmony," says Andreas Krause, who is Creative Director Exterior Design Rims at BMW. At the Bavarian maker, each wheel design is developed specifically for a model.
BMW wheel designer Andreas Krause says the biggest trend in wheels is aerodynamic optimisation.
"Flat wheels with small openings produce less wind turbulence than open wheels. This reduces consumption and, in the case of electric cars, increases the range," he says.
The wheels on the new BMW 7 Series luxury saloon are largely closed. Making them with no openings at all is not possible because the brakes need cooling.
Although e-cars brake strongly with their e-motors thanks to energy recovery, conventional brakes are still necessary, says Krause. "What I can imagine in the future is that the rear wheels are closed and the front ones offer only minimal openings."
Intelligent solutions in which apertures on the wheels open and close themselves, according to usage or speed are also conceivable, he added.
However, not all customers want closed wheels. For sporty vehicles, open wheels with cross spokes dominate. Customers also want the expensive brake system (often painted in a bright colour to draw attention) to be clearly visible, says Tumminelli.
Porsche, for example, has brake systems with the callipers painted in different colours, such as red or yellow, depending on the performance rating of the car.
Big wheels also bring disadvantages. They are heavy, reduce comfort and increase fuel consumption. The unsprung mass of a vehicle such as wheels, tyres and brakes should be as low as possible, say engineers. This reduces the load on the wheel on uneven roads and boosts safety as well as comfort and improves handling.
"The light alloy wheel will need get even become lighter in the future in order to reduce the weight of the unsprung masses, lower fuel consumption and thus increase the range," says Tumminelli.
Albert Rosello, a wheel designer at Audi, also sees a trend towards more aerodynamic and lighter wheels, especially for electric cars. In order to create the best and most handsome wheels possible, Audi is also using AI in the design process for the first time.
In the self-learning programme FelGAN, two algorithms compete against each other to create ever-better design ideas.
"FelGAN gives us fresh inspiration and suggestions for new designs. But we creatives still decide which designs to follow up on and choose for which model in the end," says Rosello. "We often only continue to use certain elements of the AI creation," says Rosello.
The programme can come up with more than 100 suggestions per second, including completely new ideas and changes to existing designs.
