“Add power and you are faster on the straights, reduce weight and you are faster everywhere - so a lighter car corners harder and faster, brakes quicker, is more agile,” the founder of carmaker Lotus Colin Chapman once said.
Take your grandfather’s car: about 60% of its total weight were probably due to steel. But today’s vehicles are a different breed.
Car firms find more and more ways to shave off weight. This improves not just their speed, but – most importantly – helps cut their fuel consumption to meet ever more stringent fuel economy standards, which in turn reduces carbon emissions and meets consumer demand. In the United States, federal fuel economy standards require automakers to improve car efficiency to 54.5 mpg by 2025.
To hit the target, manufacturers are turning to innovation – eyeing many different materials such as high-strength steels, carbon fibre, magnesium, compressed wood and even soy to shed weight without compromising safety.
Cutting a vehicle's weight by 10% can improve its fuel economy by 6 to 8%, according to the US Department of Energy. In other words, reducing a car’s weight by a mere 50kg reduces the CO2 emitted per km by up to 5g and increases fuel economy by up to 2%, says Patrick Cazuc, global automotive leader at DuPont International Operations. The Switzerland-based company works with carmakers to find innovative light-weighting solutions – such as replacing metal parts with lighter materials like high-performance polymers. Lighter cars also lead to less brake and tire wear, he says – as well as shorter braking distances, producing less waste heat.
Learning from space
When it comes go weight, it doesn’t really matter whether a car runs on fossil fuels, electricity or any other energy source, says Lyndon Sanders of Far Composites. “In electric vehicles, this extra efficiency shows up as one of two drivers, either extra range from the same batteries or reduced cost from fewer batteries,” he adds. After all, you need to be light to extend the mileage you can cover before you have to recharge the batteries.
Last year, a research project to apply the science behind Formula 1 and space satellites to make vehicles lighter won a £1.7 million grant from the UK government. Now a consortium including Jaguar Land Rover and Nissan is doing just that, with the aim of cutting the weight of steel components in cars such as the Nissan Leaf by more than half, and extend the distance a plug-in car can drive by up to a quarter.
Of course, shedding weight isn’t easy – and new materials are expensive. One obvious candidate to replace steel is one of the lightest metals – aluminium – and many carmakers have opted for it. “Aluminium has helped to abandon the general belief that a heavy car is safer than a light one,” says Rafael Fuertes, strategy and innovation head at Sapa, an Oslo-based joint venture of Orkla and Hydro that makes aluminium parts. Sapa helps automotive manufactures identify what car parts can be replaced with aluminium, and how the design of the components can be improved to make them lighter and safer. The company also collaborates with universities to develop new alloys that could sustain high impacts.
One kilogram of aluminium in a car reduces its CO2 emissions by 19kg over the car’s lifetime, he adds. And “if we include the production and distribution of fuel, then a car’s weight reduction of 100kg means a saving of 10g of CO2 per km.” Another plus is that aluminium can be recycled endlessly.
Fancy new materials
Back in 1994, Audi was the first carmaker in the world to introduce a series-produced car with a body completely made from aluminium – the Audi A8. “The need to pare back weight is in sharper focus than ever, particularly as we enter the era of the electrified drivetrain,” says Alex Fisk of Audi UK. “So we are making ever more increasingly intensive use of aluminium material mixes and carbon fibre-reinforced polymers wherever appropriate.”
The new Audi R8 supercar, for instance, uses aluminium – but also sports carbon fibre-reinforced polymer (CFRP) for the rear wall, the centre tunnel and the three-part B‑pillars. Meanwhile, the Audi A6 Avant TDI ultra is fitted with glass fibre-reinforced polymer springs, saving approximately 4.4kgs of weight, says Fisk. And thanks to aluminium, the new seven-seat Q7 luxury SUV is some 325kg lighter than the previous model, he adds – the equivalent of a concert grand piano.
A perhaps less obvious, but just as useful material is magnesium – it is 35% lighter than aluminium and 75% lighter than steel. Carmakers heat it and then pour it into a die to make various parts. While it’s even more expensive than aluminium, there are companies opting for it instead – such as Fiat Chrysler Automobiles, which has opted for a magnesium skeleton covered by a thin steel shell for the liftgate of its 2017 Pacifica minivan. The result: the weight of the liftgate has been reduced by about 10kg.
DuPont, meanwhile, is working Vizilon on a new thermoplastic composite (TPC) - a family of light-weighting solutions that includes continuous fibre-reinforced composites. The material “offers mechanical properties superior to injection-molded reinforced thermoplastics,” says Cazuc. In other words, it “has the strength of steel at just one-quarter of the density.”
Other lightweight materials are Zytel PLUS nylon resin, which can easily handle long exposure to hot oil, hot air, road salt, coolants and other automotive chemicals, and Hytrel TPC-ET thermoplastic elastomer, which is used instead of metal for air ducts, adds Cazuc. Elastomer has the flexibility of rubber, but the strength of plastic.
Then there is carbon fibre, an ultra-light and durable material. It is used in cars, but not that much – it’s expensive, so not many carmakers are betting on it just yet. For instance, while the Tesla Roadster, a high-performance all-electric sports car, is made with carbon-fibre body panels and an aluminium chassis, the Tesla Model S all-electric sedan, a more affordable option, uses aluminium for the body but no carbon fibre.
Going bio
Another alternative is Axontext, produced by a subsidiary of Far Composites, Axon Automotive. The material can be used to produce a carbon fibre spaceframe chassis – at the same cost as an aluminium alternative, says Sanders. It also allows for compression moulding and wet pressing processes, and which makes it possible to create panels for hybrid metal and carbon fibre car bodies, he adds. The Hyundai Intrado, for example, uses Axontex, which makes it 70% lighter than the same car made of steel.
Another approach are biocomposites, which are being developed by a number of firms. Muhammad Pervaiz, a biomaterials engineer at the University of Toronto, is developing hybrid lightweight biocomposite materials and structures that use renewable sources to extract nanocellulose fibres. They find their way into injection moulding and thermoforming techniques, which transform them into high-strength thermoplastic composite structures that contain carbon fibres. “We have already developed automotive prototypes,” Pervaiz says, adding that they are “at least 25-30% more lightweight” compared to conventionally-made cars.
One of the carmakers looking into biocomposites is Ford. The company is collaborating with Weyerhaeuser – one of the world’s largest producers of timber - to use plastic composite material made from cellulose fibres harvested from sustainably grown trees instead of fiberglass or mineral reinforcements. According to Ford, cellulose-based plastic composite is just as durable as traditional composites, but weighs 10 percent less.
The key to weight-loss success is how the various approaches to “light weighting” are being combined. For instance, at the Lotus Lightweight Laboratory in Hethel, England, engineers constantly try to find new ways of doing just that, which, according to the company’s spokesperson, has helped to sharply slim the latest models. For example, the 2017 Evora Sport 410 is 112 kg lighter and benefits from a power increase of more than 60 hp compared to the 2014 Evora S – while the weight of the latest version of the Lotus Elise, “the lightweight champion,” is around 41 kg below that of the previous model.
So what about steel? It’s hasn’t been forgotten - a number of companies are developing advanced high-strength steels that can provide up to 35% in weight savings, according to the Steel Market Development Institute (SMDI). It is now possible to make different types of steel that are two to three times stronger than they were a decade ago – and by making it stronger it means parts can be made thinner and hence lighter. Volkswagen, for instance, used nearly 15 % more high-strength steel in one of its latest Golf models, which made it about 100kg lighter than the previous model.
So your grandfather’s car shouldn’t feel totally estranged from today’s world of new materials; after all, steel is still in the game.