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If you have an e-mail account anywhere, the odds are good that you get some forwards. They mostly come from friends – jokes and cute stories – and many are political or indignant. Recently, I got one that really got me thinking about fuel economy and its impact on America. The title of the e-mail was, How far can you go on $500 of diesel fuel?

The graphic in the e-mail compared how far a truck could go on $500 of fuel now, versus how far it could go just last year. Even more eye-opening was how far that $500 could take you in 1999 – clear across the country.

The average Class 8 over-the-road truck has two 150-gallon fuel tanks which allow it to go about 1,800 miles without refueling. Thats based on an average fuel economy of 6 miles per gallon, as in the graphic.

One urgent question is whether or not 6 mpg is an accurate figure. In fact, data from the U.S. Department of Transportation shows that average heavy-duty fuel economy has actually dropped – from a high of around 6 mpg in 1997 to just over 5 mpg in 2006. By contrast, fuel prices have quadrupled over the last nine years due to increased crude costs and, in 2007, the introduction of ultra low sulfur diesel (ULSD). So now the same truck can go about 1,560 miles without refueling, but at a cost of over $1,200!

Interestingly, the American Trucking Associations (ATA) reports that while fuel consumption in the trucking industry has stayed essentially constant since 2000 (at about 30 billion to 35 billion gallons a year), the cost has gone from about $46 billion in 2000 to a forecasted $142 billion this year. The difference – $89 billion – is equivalent to the cost of nearly 900 million additional Class 8 tractors (at $100,000/tractor)! If the trucking industry and a major portion of the American infrastructure are to survive, costs must come down, or at least stabilize. And a major component of cost is fuel.

So lets explore the fuel economy issue for heavy-duty trucking. Lets look at the components of fuel economy and try to put some numbers around this issue. Well look at aerodynamics, maintenance, driving habits – and of course lubricants. In the end, we may be able to identify some important savings and find a magic number to quantify the whole thing.


First, lets be clear: Over-the-road trucks are not super-streamlined. Due to the trucks job description (hauling heavy loads) it has to have a rather large powerplant, a heavy frame and significant transmission and gear boxes. Moving up to 40,000 pounds of cargo, plus the weight of the tractor and trailer, requires significant power which consumes great amounts of fuel. Anything that can be done to reduce fuel consumption through aerodynamics is a major plus.

For example, according to commercial truck builder International, proper external design can improve fuel economy by up to 14 percent. The Navistar subsidiarys ProStar design gives the fuel economy improvements shown below.

Other vehicle manufacturers also are working on improvements that are of similar magnitude. Based on 6 mpg, a 14 percent improvement in fuel economy represents an additional 0.84 mpg improvement. When a vehicle is expected to go 100,000 miles or more a year, that is truly significant!

Although not strictly part of aerodynamics, vehicle design is evolving with the advent of new, lighter-weight materials and structural designs. Aluminum is being incorporated into more components of the vehicle and new chassis designs are resulting in greater strength at lower weight. No fuel economy numbers are being offered but it is reasonable to assume that there will be important fuel economy savings going forward.


As with any mechanical device, maintenance can make a difference in the performance and lifespan of a truck. Every truck fleet has a maintenance schedule which allows for periodic inspections, repairs and replacement of various parts of the vehicle. Among the items which are regularly inspected are lights (running lights on trucks and trailers are a significant expenditure for fleets), suspension systems and tires. In addition, damage which affects airflow over the vehicle can be a source of lost mileage, not to mention a safety concern.

Were all aware of the importance of properly inflated tires in maximizing fuel economy. For the trucker, this is even more important since improperly inflated or improperly balanced tires are a major factor in many truck accidents. There have been many articles done on the impact of tires on fuel economy. Bridgestone says that increasing speed results in only a slight increase in the tires impact on fuel economy. Maintaining proper air pressure and balance is an important fuel-saving practice as well as a safety issue. Tire design is also important: Proper tread design can improve fuel efficiency between 6 percent and 14 percent.

There are a number of other maintenance issues that are important to efficient operations. Proper lubrication of the chassis, properly operating shock absorbers – in fact every system on the truck needs to be in optimum working order to maximize fuel economy and efficiency.

Driving Habits

Earlier columns Ive done on passenger car fuel economy showed that driving habits make a big difference in fuel consumption. Its no different in the commercial fleet market. Columnist Jim Windsor of Heavy Duty Trucking (in 1997, no less) reported that ATAs Technology & Maintenance Council identified more than 50 areas to be examined relative to fleet fuel economy. The Number 1 impact on fuel economy identified in this study was driving habits.

The driver makes a huge difference in fuel economy, TMC found. In trucks of similar specifications and in similar service, the differences between a best driver and worst driver can impact mileage by up to 35 percent. Driver training, motivation and incentives continue to be the most cost-effective ways to get top fuel efficiency.

The Number 2 area: speed. To the surprise of no one, slowing down saves fuel. The graph (left) from TMC shows the impact of speed on fuel economy and is very telling.

I spoke with the owner of a small trucking company in the Phoenix area about the cost of his operations. His fleet averages about 6 mpg and his trucks are currently governed at 67 miles/hour. Controlling speed has resulted in much better fuel economy for his fleet, he said.

However, he added, if he lowered the governed speed further, to an even-more-fuel-saving 62 mph, he would find it difficult to retain drivers. I can understand why: The drive from Phoenix to the Los Angeles area – a major part of his business – is mostly through desert areas which are very dull and boring. The sooner you are through the better!

Another operating habit that has changed is idle time. Until recently, most Class 8 trucks averaged about 1,700 hours of idle time per year. Some of the reasons for idle time are to supply power for cab comfort (air conditioning or heating), or to run other auxiliary units which supply cooling to the cargo area. About two years ago, a major increase in the use of auxiliary power units (APU) as well as battery power for cab comfort units cut into idling practices. APUs consume about one-fifth as much fuel as does idling the engine (0.2 gallon/hour for APU vs. 1.0 gal/hr for idling).


Finally, of course, the lubricants used in heavy-duty trucks also play a part in the fuel economy equation. Everything from wheel bearing lubricants to engine oils is involved – especially engine oil.

Compared to the double-digit improvements from aerodynamics, speed control and driving habits, the opportunities for gains from lubrication may look more limited – but they are there. So next months column will offer a closer look at the role of lubricants in the heavy-duty fuel economy puzzle.

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