One of the "holy grails"of carbon fiber application is car wheels. How badly would auto OEMs love to lose those heavy steel wheels? The question always has been: Can a carbon fiber wheel meet all of the required performance specs at an affordable price? The short answer is, yes but not yet. Dymag Racing UK (Chippenham, U.K.) has developed a carbon fiber wheel that meets or exceeds many of the performance requirements of a car wheel, but price, for now, leaves this product in the high-performance category. The future, however, looks bright.
Bevis Musk, Dymag's marketing director and technical director of composites development, says the wheels comprise a forged magnesium hub/spoke system that is fastened to a carbon fiber rim by specially coated titanium fasteners. The rim is molded from a Toray Carbon Fibers America Inc. (Flower Mound, Texas) dry weave carbon fabric supplied by Sigmatex High Technology Fabrics Inc. (Runcorn, U.K.) and infused with a high-performance epoxy from Huntsman (The Woodlands, Texas) in a proprietary RTM-like process that Musk calls "high-pressure casting."It uses a solid metal casting-type mold with injection at 50 psi to 75 psi (3.45 bar to 5.17 bar). A key to process success is a lacquer-based coating that, when applied to the mold surface, serves as the mold release, but at demolding adheres to the rim, providing a durable finish that resists ultraviolet light brake-dust, salt and other corrosives encountered by race and road cars. According to Musk, the wheels come out of the tool to spec and ready to use.
Dymag tests show that the wheels have better damping properties than aluminum and magnesium competitors, with three times the impact resistance. While a standard steel Porsche GT3 RS 18-inch wheel weighs about 14 kg/30.8 lb, a Dymag carbon/magnesium equivalent weighs around 6.5 kg/14.3 lb, saving about 30 kg/66 lb per car and reducing the moment of inertia â€“ the energy required to turn and stop the wheels. The result is either a reduction in emissions, an increase in power, or both. One automaker, says Musk, reports that a weight savings of 30 kg translates to an engine power increase of 40 hp.
At $2,100 to $2,200 each, the wheels are a far cry from the $75 to $600 consumers pay for a custom wheel at the local tire shop, but for high-performance race cars and other specialty applications, Musk says they are on par with magnesium counterparts and, though more expensive than high-performance aluminum wheels, can recover the premium, in many cases, by achieving greater fuel economy.
The next step for Dymag is to reduce the cost of production and, subsequently, the cost of the finished product, with an eye toward the larger consumer market. According to Musk, Dymag's list of interested automakers so far includes custom and larger producers, such as Mosler Automotive, Cadillac/Chevrolet (Corvette), Aston Martin, Ascari, and Ford (GT).
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