Carbon Fibre Wheels Bid For Mainstream Scale

Carbon Fibre Wheels Bid For Mainstream Scale

Engineers struggle to save weight on EVs. Carbon-fiber wheels might be one of the biggest opportunities as wheel and tire sizes grow.

Regular wheels are surprisingly heavy, as you’ll know if you’ve ever rotated your tires or had to change to a spare at the side of the road. Heaviness is a quality undesirable for fuel efficiency. The weight of regular wheels has more impact on the car than just its curb weight, though reduce the weight of any component on a car and you work towards a more efficient vehicle.

It’s the properties of a car’s wheels that also influence how the reduced weight of carbon fiber components can bring about improvements.

Firstly, wheels are not “sprung” mass. Sprung mass refers to any part of the vehicle carried by the suspension, but wheels move about on the other end of a vehicle’s suspension. They and the tires follow the lie of the land, and the lower their weight the easier they’re able to do this.

Carbon fiber wheels have less inertia when they move, hitting a bump and returning to their starting position rather than being launched over it, to however small a degree. This, as you might imagine, is better for ride quality. But wheels also spin, generating rotational mass.

A spinning mass, as Carbon Revolution’s Brett Gass demonstrates with a gyroscope in the video, is harder to turn. It’s also harder to start and stop, because you’re always fighting against that rotational mass. The key here is improving that ability to start. Make a wheel light (indeed, making all four wheels light), and it takes less effort to get moving. Less effort to get moving means less fuel or electricity used, increasing mileage and range.

Carbon fiber structures aren’t just light, but also very stiff and strong–hence their use in racing cars for years. This helps prevent flex under harder cornering, something noted in the video.

While currently expensive–the full set of wheels mounted to the Porsche costs $15,000–improvements in the technology used to make carbon fiber is also bringing down the cost. It may never be as cheap as making aluminum wheels, but its benefits could make it desirable for those really serious about economy.

Bentley announced a new wheel design for the Bentayga SUV that makes them the largest carbon-fiber wheels ever fitted to a production car. Developed by Bentley’s Mulliner division in collaboration with Bucci Composites, the 22-inch wheels will be available to order later this year.

 Compared with the Bentayga’s regular 22-inch wheels, these new carbon composite rollers save 13 pounds per corner in unsprung mass. The carbon wheels are also stronger and stiffer than normal wheels, and there’s less of a loss of camber under hard G-forces. 

The carbon wheels are also safer in the event of a major impact that would damage them, as the weave pulls apart for gradual air loss instead of the immediate air loss that would happen with an aluminum wheel.

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