Australia’s Carbon Revolution may not be the best known wheel manufacturer in the world, but they are among the most interesting. Most of the brands that are known and sell in high volume like BBS, Rial and O.Z. make their wheels from metal alloys, mostly aluminum. Carbon Revolution uses carbon fiber composites. To date, they have mostly supplied their exceptionally lightweight wheels for high performance machines like the Ford GT, Shelby GT350 and Ferrari 488 Pista. Now they are looking to expand to more mainstream vehicles, especially those powered by batteries.
Carbon fiber composites aren’t a particularly new concept. They have been used in aerospace for many years before McLaren brought this lightweight and high-strength material to Formula One in 1981 and to road in the 1990s in the legendary F1. In 2013, BMW made the first use of a carbon composite structure in a relatively high volume model for the first time with the i3.
However, the approach being pitched by Carbon Revolution with a focus on the wheels may turn out to be both more cost effective and offer a greater efficiency advantage than what BMW did. Given the cost and mass of batteries, maximizing energy efficiency is critical for EVs to get the most range from the least amount of battery.
Reducing mass of any kind is a straightforward path to improve efficiency by simply reducing the workload on the propulsion system and energy storage (aka the battery). But not all mass reductions have the same impact. We know about inertia from Newton’s second law of motion. In a very simplified form it comes down to an object at rest will stay at rest or an object in motion will continue to move unless an unbalanced force is applied.
But inertia has directional vectors associated with it. Accelerating a vehicle requires a force in the direction you want to move. In the case of a wheel, there are actually several important directions, horizontal, vertical and rotation.
Vertical inertia must be overcome to follow the contours of the road such as bumps or potholes. As wheels get larger, which they seem to be inexorably doing for aesthetic purposes, they get very heavy and ride quality degrades rapidly because the wheel can’t accelerate up or down fast enough to follow the road, thus transmitting those forces into the cabin.
Horizontal inertia has to be overcome to accelerate, brake or steer the vehicle. However, that is achieved by actually turning the wheels from the engine or motors so rotational inertia has to be overcome. Again, the larger the diameter of the wheel, the greater the rotational inertia and this turns out to be a larger factor in EV efficiency than just the sheer mass of the wheel. If two wheels of different sizes have the same mass, the one with the weight furthest from the center will take more energy to drive.
That’s where carbon fiber wheels can be a huge benefit for EVs thanks to a mass reduction of 40 to 50% compared to a similarly sized alloy wheel. According to Carbon Revolution CEO Jake Dingle, carbon wheels on a typical SUV can save up to 130 lbs of mass that moves vertically and rotates. Given the bulk of batteries which can weigh up to 1,600 lbs in the Ford F-150 Lightning or more than 2,900 lbs in the GMC Hummer, that’s a notable reduction that would improve driving range.
But there are more benefits to carbon composite wheels. Compared to aluminum or steel, the cross-linked fibers in the composite structure dampen out road impacts that are transmitted more directly through metal. The result is up to 5 dB less road noise coming into the cabin. Since EVs don’t have an engine to mask out other ambient sounds, reducing those sounds at the source helps to keep things quiet without adding more sound deadening matting.
Carbon composite wheels also offer more flexibility in shaping that isn’t possible with cast or forged aluminum. This can enable more aerodynamically shaped wheels that reduce drag and of course improve efficiency.
On an EV, using a larger diameter but narrower wheel can help reduce aerodynamic drag while maintaining a reasonable contact patch for the tire on the road. That’s what BMW did with the i3. If those larger, narrower wheels were made of carbon fiber composite instead of aluminum, they would have had an even more positive effect on range.
Carbon Revolution’s wheels are manufactured through a resin transfer molding process that doesn’t require manual layup of the fibers as would be done for something like the structure of a high-performance sports car. The dry fibers are significantly cheaper than the resin pre-impregnated fiber used in other processes and doesn’t require curing in an autoclave. The company is doing concurrent engineering of its products and processes to increase production capacity and automate many of the steps.
While carbon fiber wheels still carry a significant price premium today, that is shrinking as the volumes go up. This year, the company is projecting production of about 50,000 wheels and at 1 million units expects value parity with alloy wheels. Carbon Revolution’s first SUV program is launching toward the end of 2022 and Dingle is expecting about 15 vehicle programs over the next six years with a significant production expansion by mid decade.