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A lightweight material is helping makers of heavy-duty trucks produce a new generation of tractors.

Unlike the boxy, extended-nose tractors long favored by American truck drivers, these new tractors are curvaceous and slippery.

Heavy-duty truck makers are turning to sheet molding compound to help build the tractors. While they seek a contemporary design, the bottom line is aerodynamics. The more aerodynamic the tractor, the less fuel it will consume. And that means lower operating costs for fleet owners and owner-operators.

SMC has been used in the smallest of cars to the heaviest commercial trucks. But the greatest growth in the use of SMC has been in heavy trucks in recent years. Nearly 54 million pounds of SMC is being used on 1997-model heavy trucks, said Troy, Mich.-based SMC Automotive Alliance, an association of 26 molders and raw materials suppliers.

That's up 157 percent since 1993.

Kenworth Truck Co. uses the greatest volume of SMC — a combination of resin, glass and filler — on its new T2000 tractor. Barry Langridge, Kenworth's general manager, called it Kenworth's most aerodynamic truck ever, saying a 6 percent improvement in drag coefficient provided a 3 percent improvement in fuel economy.

Kenworth expects to use 21 million pounds of SMC in 1997, nearly all of it on its T2000. Kenworth uses nearly 1,000 pounds of SMC on each T2000 it builds. That represents the largest single use of SMC on any one vehicle, the SMC Alliance said.

``Their move to aerodynamics is fueling the business for all of us,'' said Richard Pistole, engineering director at Cambridge Industries' Commercial Truck Group, a supplier of SMC and plastics.

Kenworth uses SMC on the T2000 hood, cab door assembly, aero roof, bumper, storage doors, fire wall assembly, fuel tank fairings, sun visor and structural pillars.

Truck makers are attracted to

SMC's formability and light weight, said James Grzelak, sales engineer at Eagle-Picher Plastics Division.

``We can give the shape and fit and meet all of their durability requirements. For Kenworth, it's a significant cultural change for them,'' said Grzelak, who also is the alliance chairman.

The heavy-duty truck industry has been dabbling in SMC since the mid-1980s. Truck manufacturers began using the thermoset composite for hoods about 10 years ago, and interest has progressed slowly since, said Thomas Seiter, director of sales and marketing at Cambridge Industries' Commercial Truck Group.

Navistar International Transportation Corp. has been using limited amounts of SMC. The cost savings is a huge consideration, said David Johanneson, group vice president of truck businesses.

``On a Class 8 truck, weight reduction also is a very significant consideration,'' he said. ``The biggest area we've used it is in hoods, air fairings and battery boxes.''

Just how much further Navistar plans to go with SMC and other plastic products is unknown. While Navistar wants the weight savings, the truck maker first will test SMC and other plastics to make certain the materials are reliable and durable, he said.

Volvo GM Heavy Truck Corp. also believes in the benefits of SMC. When the truck maker unveiled its new VN series in September, the Class 8 tractors had nearly 600 pounds of SMC. VN tractors use SMC for the hood, bumper, sun visor, chassis fairings, fuel tank fairings, side air deflectors, cowl, fender extensions, raised roof assembly and engine cover. However, Volvo GM used high-strength steel for its cab, shunning aluminum and other materials.

Before the T2000 and VN bowed this year, Ford Motor Co.'s AeroMax 9500 tractor boasted the greatest use of SMC. When AeroMax was unveiled in 1995, it carried a record 450 pounds.

Besides its formability, SMC offers heavy-duty truck makers the opportunity to use a lighter, corrosion-resistant material and reduce the complexity of components.

The largest market for SMC is in light-duty trucks, vans and sport-utilities, where a projected 94 million pounds will be used in 1997, a 27 percent increase since 1993. Another 73.3 million pounds of SMC is expected to be used on cars this model year, up 40 percent since 1993. Besides the 53.9 million pounds in heavy-duty trucks, another 15.7 million pounds will be used in medium-duty trucks.