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A rendered CAD model of the rear suspension shows the thermoplastic composite components in red. The glass-reinforced nylon 6 parts are the primary springs, and the upper control arms function as secondary springs in roll conditions.

Racecar with composite-intensive suspension gets track tested in 2015

The tangy yellow-colored 1986 Honda CRX emblazoned with SANLUIS Rassini on its hood uses a patents-pending rear suspension as a replacement to its most recent setup of coil-over-springs and a straight axle with a Mumford linkage for lateral control.

“We’ve converted it to a dual-cantilever thermoplastic spring in the rear. It’s very similar to a double-wishbone geometry. The thermoplastic upper control arms are coupled with what’s very similar to a Watt’s linkage. That means during a two-wheel bump, the rear wheels move together. But when the car goes into roll, the coupling linkage locks the arms and those arms flex to add roll stiffness,” Jonathan Spiegel, Polystrand Inc.’s Senior Engineer, told Automotive Engineering.

The racecar will compete in the Sports Car Club of America’s (SCCA) Grand Touring Lite (GTL) 2015 race season on various tracks in the U.S. Project GTL partners are Polystrand, PPG Fiber Glass, the University of Alabama at Birmingham (UAB), and SANLUIS Rassini.

Polystrand provided the thermoplastic composite material. PPG supplied the continuous fibers for reinforcement of the thermoplastic material. UAB conducted materials property evaluation and molded the glass-reinforced springs and upper control arms, while SANLUIS Rassini handled suspension modeling, fabrication work, as well as final rear suspension assembly.

The racecar will compete against other purpose-built, highly modified series production sports cars, starting in the spring of 2015.

“We’ll be putting the rear suspension system under a real torture test. If we run the minimum number of SCCA’s GTL races, the suspension will experience several thousand miles of racing. Each race means continual high-stress on these lightweight, recyclable components,” said Spiegel, who designed the racecar’s suspension layout.

Bob Friedrichs, SANLUIS Rassini’s Vice President Engineering Suspension Group North America, noted that “the development of the GTL project in collaboration with Polystrand and PPG is an important one. It allows for testing of new continuous fiber thermoplastic technology for suspension springs and provides us with a lot of [vehicle] limit handling data in a short period of time.”

Spiegel estimates that the front-wheel-drive racecar shed more than 100 lb (45 kg) by replacing its all-steel rear suspension with a configuration featuring glass-reinforced nylon 6 springs and upper control arms attached to a steel subframe.

“The suspension loads are now fed directly into the frame structure rather than being in the unibody, so the car no longer needs all that supporting structure. In a production car that supporting structure would take up rear-passenger compartment volume and trunk space,” said Spiegel. “The prototype suspension not only reduces the mass but we can put what mass there is down lower, so that will help with the car’s handling.”

For SANLUIS Rassini, the world’s largest designer and manufacturer of leaf springs for light-duty vehicles, developing lightweight suspension components for future production applications is important. According to Friedrichs, “A commercially viable composites-intensive suspension for passenger cars would absolutely be a game changer.”

Weight savings between 30-40% are possible. “The implication that would have on lightweighting and CAFE standards would be huge,” Friedrichs noted.

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