Specs that Payback

| July 01, 2009

Andy Zehnder, Kenworth’s on-highway manager, says, “Side extenders deflect the air around the gap between the tractor and trailer to cause it to reattach quickly to the outside edge of the trailer.” Fairings alone, he says, decrease wind resistance 2 percent to 4 percent, resulting in 1 percent to 2 percent fuel savings.

Mack’s Warmkessel says side shields and side shield extenders help close the tractor-trailer gap. “Chassis fairings, including fuel tank fairings, aerodynamic bumpers and aero mirrors, are part of the U.S. Environmental Protection Agency SmartWay package option offered on Macks,” he says.

Zehnder advises to avoid external air cleaners. Unless you drive only in a quarry or at low speeds on secondary roads, they increase wind resistance far too much.

Ken Marko, Peterbilt’s market planning manager, says his company has several new aerodynamic products on both aerodynamic models and traditional models. “They give 24 percent less drag and up to a 12 percent fuel economy improvement when tested at 65 mph,” he says.

The packages include a roof fairing and trim tabs to route air up and over the trailer, a sleeper extension to route air around the sides of the trailer, aerodynamic mirrors, an aero bumper and even an aerodynamic battery box. He reports Peterbilt learned a lot from its Model 372, an aero cabover introduced in the late 1980s, about how to control airflow.

Volvo’s Bio suggests spec’ing a premium interior, but avoid an unusual color to ensure you don’t alienate buyers when it’s time to sell. Crear lists premium seats and a full gauge package as desirable options at resale.

Another option to spec is 22.5-in. diameter, fuel-efficient, low-profile tires that are SmartWay-certified to reduce rolling resistance. Wide singles should also be considered.

George Meiners, of Schneider National, says the best value for owner-operators comes with mid-range engines and drivetrains. He says, “Don’t spec’ extreme horsepower; 450-475 is more desirable than 550s. Heavy-duty transmissions and axles add both cost and weight.” Warranties are much cheaper on midrange components that are made in much greater numbers and have to transmit less torque.

Mack’s Warmkessel says, “You don’t need 600 horsepower to haul 80,000 pounds.” He thinks 425 hp is enough. Bio also believes an engine like Volvo’s D13, at 485 hp and 1,650 lb.-ft. of torque, is right for most operators needing good muscle under the hood.

Proper gearing for fuel economy is essential. “The engine of today likes to run in the 1,300-1,400 rpm band,” Freightliner’s Harrington says. “It is no longer wise to say, ‘I only run 3.55:1 gearsets.’ ” Experts tout the high value of choosing the tire diameter, axle ratio and transmission top gear ratio, so the engine will cruise in the “sweet spot” at your highway speeds. And multi-torque arrangements, along with digital in-dash fuel economy calculators, are highly recommended when you have a hired driver or two. Multi-torque engines add beef to the torque and power curves in top gear only, killing the incentive to downshift too early because doing so won’t reward the driver with more power.

Kenworth’s Zehnder says a GPS system can reduce out-of-route miles by about 3 percent a year.

Lightweight components, such as aluminum wheels, will also help save fuel and increase payload. When it comes to more exotic options like aluminum air tanks, however, Crear says, “You’d need an engineer to make the decision.” International’s Shust says, “You’ll get savings that pay back your cost with lightweight components, if you can add payload. Weight savings for fuel economy alone may or may not work.”

Marko advises looking at an all-aluminum cab and aluminum in the chassis, such as in spring brackets on Peterbilts.

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