Winds of Change

| December 12, 2008

Will record fuel prices drive more truck buyers to seek sleek?

Dima Rips is a classic truck fan, and his favorite model is a Kenworth W900. “I love the style and the look,” says the Russian-born owner-operator, who has driven in the United States for the past 13 years. “I love everything about classic trucks. Everything but their efficiency.”

With their external air cleaners, Texas bumpers, chromed tanks and big, long hoods, classic trucks like the W900, Peterbilt 379 and Freightliner Classic remain popular today – despite major gains in aerodynamic design and increases in fuel prices.

Today’s classic truck models do cut through the wind better than their predecessors thanks to incremental improvements in design, say truck engineers. Most have roof and skirt fairing options, angled windshields and other modern wind-friendly touches, like integrated sleepers.

When it comes to fuel economy and engine power, however, classic trucks can’t compare to their aerodynamically tooled counterparts, experts say. Driver behavior and specifications may have a bigger impact on overall fuel efficiency, but owners of more curvaceous cruisers save thousands of dollars in fuel every year and have more power available to them at higher speeds, all things being equal. When Rips bought a Kenworth T600 to replace his last rig, he focused on fuel efficiency. “There was no doubt in my mind that my next truck was going to be aero,” he says. “I strongly believe that trucking is a business, and the bottom line dictates the rules. Why would I want to pay extra to push the air?”

Sales driven
Rising fuel costs are causing truckers like Rips to consider more aerodynamic models, some truck makers say. “It’s really changing the way owner-operators approach buying a truck,” says Bob Weber, an engineer with International Truck and Engine Corp. “The thing at the top of their minds is fuel price.”

In fact, the classically styled 9900 and 9900i represent a shrinking percentage of International’s Class 8 truck sales, says Ron Schoon, manager of aerodynamics. “Classic sales are going down because of operating costs.”

Other manufacturers aren’t so sure. “It’s too early to really see a shift,” says Peterbilt Chief Engineer Craig Brewster. “Fuel prices are something that they’re watching. If they remain high, we may see some migration to aerodynamic models.”

“It’s hard to measure whether owner-operators are choosing aerodynamic trucks over classic trucks,” says Volvo designer Frank Bio. “Buying trends change over time. Maybe if fuel is becoming more expensive over time, owners realize aerodynamic is a way to save that you can’t ignore anymore.”

Truck makers say one reason fuel prices might not yet impact owner-operator buying habits is that many are getting higher rates or fuel surcharges, which can cover any mpg losses produced by truck styling.

Still, if the surcharge is based on a 5.5 mpg standard, a driver with an aerodynamic truck reaching fuel efficiency levels closer to 7 mpg has much to gain financially from a more streamlined tractor.

In fact, an aerodynamic truck that gets 0.9 mpg better fuel economy than a classic truck can save its owner more than $3,400 a year.

Up on the roof
The main aerodynamic difference between traditional and aero trucks starts at the roofline.”The things that cause drag are those areas that have an abrupt change in flow,” says Volvo’s Ed Saxman. “The biggest thing is the top of the trailer. We learned that in 1983 when we were the first manufacturer to put a fairing on the truck roof.”

Today all manufacturers offer roof fairings that push air up and over the cab and trailer and many owner-operators have come to accept them even on classic models, which typically have less angled roofs. In some cases, owner-operators spec flat roofs, which push air over the cab -and into the brick wall-like front of a standard van trailer.

“If there’s nothing on the roof of the cab to throw air over the trailer, the air is like hitting a billboard,” says Tom Davis, Mack’s highway product manager.

Designers of classic models have taken this into account over the years. Peterbilt’s recently discontinued special edition 379X was not available with a flat roof -nor did its slightly sloped roof and 70-inch sleeper extend to the 13-foot roofline of the typical box van. This kind of setup is fine, if not advantageous, for truckers who haul flatbed, tankers or other trailers that are lower than the roofline. Truckers who operate at slower speeds can also spec lower rooflines because the impact of air resistance on fuel efficiency goes down as speed decreases. But for most over-the-road truckers, the penalty paid for a sleek-looking, flat roofline is substantial.

The difference in drag between a flat roof and a roof fairing that pushes air over the top of the trailer is as much as 23 percent, according to Volvo engineers. That translates to an 11 percent fuel efficiency penalty paid by owners of van haulers with flat-roofed trucks.

“If you’re going to run full-height van bodies,” says Peterbilt’s Brewer, “you need to have a full-height aerodynamic roof.”

Streamlined
Beyond the roof, many items combine to affect airflow. Hood design, headlamps, wind visors, mirrors, windshield angle, bumpers and A-posts all receive lots of attention during design. “Anything that’s square shaped – especially leading edges -causes drag,” Brewer says. “The rounder you can make them to a point improves aerodynamics.”

Chassis fairings, for example, which cover uneven surfaces such as toolboxes and fuel tanks, help air flow smoothly down the sides of cabs and can add 1 percent to 2 percent to fuel efficiency, Kenworth says. Depending on specifications, classic trucks typically have a mix of surfaces, which can impede airflow. Even small items, such as a sun visor, can dramatically impact aerodynamics. When Peterbilt designed its recently released Model 386, an over-the-road tractor aimed at the fleet market, the company tested more than 80 sun visor designs using air tunnels and computer-aided computational fluid design.

“We refined designs to one that provided the least aerodynamic drag while still providing sun visor features,” Brewster says. “All of the elements that are out in the air flow work as a system. If you change one thing, that can really hurt the impact elsewhere and degrade performance.”

Many of the features most popular with classically inclined owner-operators impede airflow. Large, flat, stainless steel Texas bumpers, for example, push air instead of channeling it around the hood. This has a big effect on a truck’s ability to move in the wind, says Volvo’s Bio. “Energy is being stolen from the vehicle and imparted to the air every place it eddies,” he says.

“Even bug deflectors or shields have an aerodynamic penalty of up to 5 percent,” says International’s Weber. That translates to a 2 percent to 3 percent drop in fuel efficiency. “It’s on the leading edge of the hood. All the airflow is trying to get around the hood, and by adding a bug shield, you’ve increased the area.”

Windshields are also a big factor. Classically designed trucks have more upright windshields that end at nearly right angles at the truck’s A-pillar. Aerodynamically styled trucks feature windshields that lean back. The windshield on International’s 9000, for example, is set at a 28-degree angle, allowing air to flow up and over the cab. At the same time, the A-pillar is rounded, channeling air around the truck. “On classic trucks the vertical windshield blocks a lot of air,” Weber says. “The air stagnates, reaches a high pressure and creates drag.”

Today’s engines also take a toll on aerodynamics. Because post-October 2002 engines run hotter, they require larger, redesigned cooling systems – a major challenge for truck makers. “Additional cooling has always come at the expense of aerodynamics,” says Matt Markstaller, test center project engineer for Freightliner. “The new engines and their increased heat rejection have given us the opportunity to take a new look at this challenge. We have made great progress in providing increased cooling without sacrificing aerodynamic efficiency.”

Axle-forward design, a popular element of classic truck styling, makes matters worse, says Mack’s Davis. “Any time you move the axle forward, the cooling system has to be changed.” Raising the cooling system brings up the nose of the truck, which causes more air to hit it, Davis says, “Instead of a teardrop design, it flattens it out.”Axle-back configurations allow engineers to slope the hood, wrap the bumper and flare fenders, giving air a place to go and lowering resistance.

External air cleaners and stacks also foul airflow. The latter, for example, can reduce the effectiveness of cab extenders.

Distinctive versus classic styling
While most owner-operators still dream of long, straight hoods, shiny air cleaners and chromed stacks, tastes are beginning to change, some truck designers say. At the Mid-America Trucking Show, International surveyed show truck owners and asked them what they wanted out of design. The answer was suprising.

“Owner-operators want distinctive styling – not necessarily classic styling,” Weber says. “These are the Pride & Polish guys. They’re hardcore image guys.”

The Freightliner Coronado, launched in 2000, was a step in this direction. While the truck was touted as a classically designed, big-hooded owner-operator truck, “it’s a very good-looking, distinct vehicle that also offers the latest in aerodynamics,” Markstaller says.

The new Volvo VT 880 is also a hybrid, featuring streamlined design with classic touches. But demand is still strong for traditional models. Fleets spec them to attract drivers, and owner-operators still desire them.

Mack, for example, recently launched its Rawhide regional hauler, which is being marketed to owner-operators with the slogan: “Legendary performance meets classic style.” The truck features a big stainless bumper, 6-inch chromed stacks and air horns mounted on its flat roof.

That emotional appeal is important, says Mack’s Tom Davis. “There’s something to be said for having pride in what you do. That classic configuration says a lot about their professionalism.”

Ultimately, the choice between classic design and aerodynamic efficiency comes down to personal preference. Owner-operator Stanley Ryan, for example, runs four aerodynamic Volvo 610 models, but their sloped hoods had little to do with his purchase decision. “I love the truck because of cab roominess,” he says. “I don’t like the blind spots produced by square features. I was in a classic truck the other day that had a small cab and a narrow windshield. I didn’t like it.” But most owner-operators who choose the aerodynamic option do so because of its bottom-line impact.

“All other things being equal,” says owner-operator Dima Rips, “if an aero truck could save me $5,000 to $10,000 a year extra, I sure would know how to use it.”


The aero payoff
At 65 miles per hour, aerodynamic trucks average 15 percent more in fuel efficiency than similarly spec’d classic trucks, according to one Kenworth study. For example, if you average 6 mpg in a classic truck, you should average 6.9 mpg in its aerodynamic twin. While it doesn’t look like much up front, that fraction can be worth thousands of dollars a year, especially if you drive mostly over-the-road.

The faster you go, the greater percentage of fuel efficiency is eaten up by drag. Says International’s Ron Schoon: Aerodynamic drag represents about 50 percent of resistance at 65 mph; at 75 mph, 70 percent of resistance is air.

Going from 0 to 50, the difference isn’t that dramatic. Owner-operators who haul in cities or who rarely go over 50 mph might not notice much of a financial or horsepower benefit in an aerodynamic model.

Highway drivers won’t just see the difference in their wallets, they’ll feel the difference in power. At 70 mph, aerodynamic trucks have a 56-hp advantage over their squarer cousins, says Volvo’s Ed Saxman.


Old style, new tricks
Owner-operators who are hooked on classics can still improve their fuel efficiency:

  • Add roof fairings, says Volvo’s Ed Saxman. “Cover the trailer, if you have a flat roof conventional.”

  • Close the trailer-tractor gap, says Mack’s Tom Davis. A space of 30 inches to 36 inches is better than gaps larger than 40 inches. But don’t forget to keep trailer clearance in mind.
  • Add side fairings to cover gaps between tool boxes, stairs and fuel tanks, Davis says.
  • Minimize the effect of add-ons, says Kenworth’s Mike Dozier. When adding external parts like spot mirrors, a single mounting arm is better than multiple arms. “Once the air gets in between the arms, it results in higher drag,” Dozier says. Aerodynamic mirrors can save as much as 2 percent in fuel efficiency over squarer models, Kenworth says.

What you gain
Potential fuel economy improvement in MPG*

Full roof fairing
(for use with van trailer) 5-10%
Cab extenders 2-4%
Chassis fairings 1-2%
Air cleaners (underhood) 1-2%
Aerodynamic mirrors 1-2%

*percentage not cumulative


Do the numbers
Assume an annual run of 120,000 miles, 100,000 of them at 65 mph. An aerodynamic truck that gets 0.9 mpg better fuel economy than a comparable classic truck at highway speeds will save $3,400 a year.

CLASSIC FUEL USAGE
100,000 miles

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