Big Rig Basics: More Miles, Fewer Gallons
December 1, 2010
Attention to your driving habits, maintenance diligence and your truck’s aerodynamics will help you maximize fuel economy
If you don’t mind burning hundreds of dollars in fuel needlessly each week, don’t read any further. But if you want to squeeze the most out of every gallon you buy, here are money-saving tips from some of the best in the business.
The person behind the wheel is the biggest factor in reducing wasted fuel. How you drive will help determine your fuel savings. As a plus, many of the best practices for increasing fuel economy do double duty in prolonging equipment life.
Driving too fast is the biggest cause of reduced fuel mileage. Every mph increase above 50 mph reduces fuel mileage by 0.1 mpg. Increasing speed from 60 to 70 mph cuts fuel economy by 1 mpg.
Owner-operator Leonard “Lennie” Bower has limited his highway speed to 63-64 mph for years, keeping fuel costs low and extending component life. He practices slow starts and stops. He gets 6.4 mpg. Last year, when he pulled the wheels off his back axle to inspect the brakes, he still had 50 percent of his brakes left after 600,000 miles.
Independent Brian Kufahl runs four Freightliner trucks and three 48-foot trailers in his Marathon, Wis., fleet. His loaded trucks consistently hit close to 9 mpg, with a best of 9.1. Most of the time, Kufahl and his drivers set cruise control at 60 mph. Beyond that, drivers are allowed one hour a day at 65 mph for passing slow traffic, Kufahl says. He also has his engines’ rpm set to enhance fuel efficiency, not speed.
“Some people will say they can’t make good time,” he says of slower speeds. “But if they would keep the left door shut, they can make time. I’ll see some of the same owner-operators pass me three or four times” in a day.
Owner-operator Gary Adams of Garland, Texas, keeps his rpm between 1,200 and 1,500 when shifting. He typically runs the speed limit but would drive slower if he didn’t have as many time-sensitive loads. He regularly gets 6.7 to 6.9 mpg, and once hit 8.5.
Owner-operator Henry Albert of Statesville, N.C., pays attention to geography in his driving. He doesn’t stop at rest areas or truckstops that are in valleys. “I only stop at the top of hills or level ground if I can help it,” he says. “If you have to go up a big grade coming out of a truckstop, it can cost $10 to get up to speed.”
Albert runs the speed he needs to meet his deadlines. “If I’m running light and I’m not in a hurry and there’s a heavier truck ahead of me, I don’t step out to pass him. I use less fuel, and he’s breaking the air for me,” he says.
Adams recommends knowing your route options well enough to make choices that can enhance fuel economy. For example, “Cement gives you better mileage than asphalt, which seems to roll under your tires a bit,” he says.
How you take care of your equipment can make a difference in lifting fuel mileage. Improvements from maintenance practices such as monitoring tire pressure and changing filters add up.
Kevin Koorenny of Redlands, Calif., has owned his 1996 Freightliner Classic since becoming an operator under his own authority six years ago. Since he’s owned it, he’s increased his fuel mileage from 4.5 to 6.5 mpg, even getting as high as 7 on occasion.
“I keep my tires inflated at the level the manufacturer recommends,” he says. “I don’t run with 95 pounds of air in my tires like a lot of people do. I check inflation every week.”
Koorenny watches his air filter and replaces it every three months. “It gets a little expensive, but they are fairly cheap. I figure a clean air filter helps the engine breathe.
Checking tire pressure during your pre-trip routine will pay off. Every 10 psi a tire is underinflated reduces fuel efficiency by 1 percent.
Kevin Koorenny pays attention to maintenance items such as monitoring tire inflation pressure and replacing air filters to maximize fuel economy on his 1996 Freightliner. (Photo courtesy Kevin Koorenny)
Tires flex more as speed increases. Flexing leads to increased friction, higher tire temperatures and reduced fuel mileage. Rolling resistance increases as a tire flexes during motion. Cooler-running tires operating at lower speeds are more fuel-efficient than tires that run hotter.
Replacing a dual-tire setup with one extra-wide tire increases fuel efficiency 5 percent, Michelin says. Kufahl says he’s improved fuel mileage by adding wide-base tires, which are on all of his drives and trailers.
If you can afford it, buy an auxiliary power unit. Compared with burning up to a gallon of fuel per hour of idling, a fuel-efficient APU will burn only 0.1 gallon and keep you cool or warm as needed – non-diesel, battery-powered APUs are likewise on the market to eliminate fuel needed for idling entirely.
Pay attention to your oil. Oil thickens at low temperatures, leading to increased fuel consumption. Synthetic oil is less affected by temperature, which makes it more fuel-efficient.
Change your air and fuel filters at the intervals recommended by your truck manufacturer. Regularly inspect charge air hoses and clamps to minimize air leaks that can reduce fuel efficiency.
Check your rig for proper alignment. If your tractor is out of alignment by only a quarter-degree, that sideways pull will reduce fuel economy.
A truck uses energy to overcome aerodynamic, mechanical and rolling resistance. For a truck traveling 55 mph, about half the energy is used to move air around that truck, Kenworth notes. At 65 mph, the energy usage to cut through the air rises to two-thirds. The more you can ease the flow of air around your truck, the better your fuel economy.
Depending on what aerodynamic devices you use, your aerodynamic drag will decline and your fuel economy will improve. Engineers note a 2-to-1 ratio – 2 percent reduction in drag generates a 1 percent fuel economy gain. For example, a full roof fairing would produce the greatest fuel economy improvement of 5-10 percent, while aerodynamic mirrors and air cleaners would improve it 1-2 percent.
Kufahl’s committed to aerodynamics. His Freightliner Cascadias are spec’d with 72-inch raised roofs, short wheelbases, chassis skirts, aerodynamic bumpers and direct-drive transmissions. His trailers are outfitted with skirts from in front of the landing gear to the trailer end with a trailer tail. “When I skirted my trailer, I pulled a full mile to the gallon better,” he says. “That doesn’t count the trailer tail or nose gap fairing.”
Brian Kufahl and his son have installed factory-built and homemade aerodynamic devices on Kufahl Transport tractors and trailers.
To reduce wind resistance, Koorenny moved his 48-foot Utility van about 18 inches closer to his cab. That positioning also helps in weight distribution to achieve maximum loads.
Adams prefers the classic, boxy-hooded truck look, but he’s owned the more fuel-efficient Kenworth T600s for almost 20 years. “Keep as low a profile as you can,” he says. “Don’t allow much space between the back of your cab and your trailer or load. That makes a big difference for me.”
Kufahl recommends taking advantage of the U.S. Environmental Protection Agency’s SmartWay Transport program (www.epa.gov/smartway), which details the effectiveness of various fuel-saving measures. The website includes calculators for single owners and fleets to measure your fuel savings.
“There isn’t a silver bullet that will get you a mile per gallon,” says Albert. “You have to look around for a tenth here and a tenth there.”
Shifting and Cruise Control
Use restraint when accelerating from stop, advises Kenworth. In its white paper on fuel economy, the truck manufacturer says short-shifting at 1,100 to 1,200 rpm in all the low-range gears limits fuel consumption. The step to high range requires more rpm. Use 1,500 rpm as the maximum shift point. “Lug the engine to 1,150 rpm before downshifting. The upper end of the power curve – 1,500 to 1,800 or 2,100 rpm – has the most severe fuel burn rate,” the company says.
Kenworth recommends using cruise control frequently. Set the cruise as soon as you are up to speed. Choose a lane that avoids merging traffic and other slowdowns that may force you to turn off your cruise control and lose momentum. You burn more fuel every time you need to regain speed. Constant speeds save fuel, the company notes.
Out-of-Route Miles Cost
Route management is another important factor in fuel economy. Out-of-route miles cost time and money and burn more fuel.
Kenworth estimates that out-of-route miles may account for from 3 to 10 percent of a driver‘s total mileage each year. For example, if an operator drives 100,000 miles a year at 6 mpg, out-of-route miles of 3 percent – or 3,000 miles – require 500 extra gallons of diesel fuel. Multiply that by $3 a gallon and the operator spends $1,500 in additional fuel costs