You probably don't think about your car's wheels that much, but to state the exceedingly obvious they're an essential part of every car.
They're also 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.
Carbon fiber, however, is light. So could carbon fiber wheels be a match made in heaven, an ideal way of improving the efficiency of future vehicles?
Possibly so, though for the meantime, as demonstrated by Jay Leno in his latest video (via Motor Authority), they're aimed at improving performance.
Why go lightweight?
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 Revolution wheels tested on Jay Leno's Garage
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.
And while this is subjective, carbon fiber also looks pretty cool.
Few of us are immune to the joys of aesthetics on our vehicles, and those who enjoy making a statement about efficiency as much as they enjoy efficiency itself will no doubt get a kick from running carbon fiber wheels...