Specs that Payback

| July 01, 2009

The days of the prototypical heavy-duty truck with a long, straight hood and a wheelbase that reaches halfway across Texas are disappearing. Also vanishing for most truckers are overnight idling and insistence on maximum horsepower.

Yet, spec’ing your truck to improve aerodynamics, reduce wind drag and enhance fuel economy in a more highly regulated environment need not be solely an exercise in shaving pennies per mile. Chances are you’ll see the road better, feel less fatigued because of a smoother ride and less noise, shift less than you ever imagined you could because of better torque, and spend less time under the truck maintaining it.

Unless you spend most of your time well below highway speeds, your fuel bill is probably half spent pushing air. Today’s rigs are aerodynamically optimized by not only making air flow smoothly around the front of the tractor but by attempting to make the tractor and trailer function as an aerodynamic unit.

Freightliner’s Keith Harrington notes the fuel savings of aerodynamic design. “When basic aero cabs are equipped with roof fairings, cab side extenders and chassis side fairings, you have optimized the aerodynamics of the vehicle,” he says. “Each of these devices adds about 1 percent in fuel savings.”

Jerry Warmkessel, Mack’s marketing manager for highway products, advocates a fresh look at wheelbases to use the tractor aerodynamics to reduce trailer drag. “Keep the tractor-trailer gap close,” he says. “Too much gap will cost you more in fuel. To do this, you’ll have to remember that long-wheelbase tractors always tend to increase the tractor-trailer gap.” He suggests a 112-in. to 116-in. BBC (bumper to back of cab) dimension rather than 120-in. He says you’ll also need to order a sliding fifth wheel to optimize the gap.

Mike Morino, an International truck sales engineer, says you might want to save weight and cost by choosing a short wheelbase and then reducing the length of the slider appropriately. If you do, you won’t be sacrificing ride quality, he says.

“In current products, the idea that a longer wheelbase gives a better ride is not true, it’s a myth. There have been so many advances in ride technology, you don’t need to spec’ a long wheelbase. It’s only for appearance, and it’s costing you a lot of money,” he says.

Be careful how far you trim the cab vertically. Steve Crear of Schneider National Finance recommends not going below a cab height of 70 inches. “A sleeper that’s desirable will impact price in a positive way on the back end,” he says. “A lower height ends up going for a discount at sale time. A 72-in. or 75-in. standup sleeper is worth even more.”

Frank Bio, Volvo’s truck product manager, says Volvo’s cab side extenders can also close the cab-to-trailer gap. “There’s a trim tab on the roof fairing that matches the aerodynamics to the trailer gap,” he says. “It adjusts as necessary. The buyer runs the trim tab in different positions, depending on the tractor-to-trailer gap, and it can give about a 1 percent fuel savings. It costs about $275 and can pay for itself in two tankfuls of fuel.”

He adds that side fairings help with crosswinds. Without them, the wind blows under the truck at an angle from the front that tends to slow it down.

Truck profiles clearly matter these days. Crear says, “The square-nosed conventional is out of style, and we’ve been recommending the aero models to our owner-operators for at least the last three years. All the truck manufacturers offer competitive, aerodynamic trucks. I recommend you specify side and roof fairings – anything that will maximize slipperiness.”

Debbie Shust, International product planning and strategy manager, says, “Air fairings pay for themselves in a matter of months. You should specify these – side extenders and skirts. On Internationals, the aero treatments include an aerodynamic bumper design, fenders and a front axle fender that runs around the wheels.”

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