Tires, other factors influence fuel economy

Aug. 1, 2008
All commercial fleets are looking for ways to mitigate this escalating diesel fuel expenses by increasing fuel economy and minimizing any unnecessary miles

With the continuing rise in the cost of a gallon of diesel fuel, all commercial fleets are looking for ways to mitigate this escalating expense by increasing fuel economy and minimizing any unnecessary miles.

To do this most effectively, it is important to consider the many factors that can affect vehicle fuel economy, said Al Cohn of Pressure Systems International (PSI). The company is the manufacturer of the Meritor Tire Inflation System by PSI, an automatic tire inflation system that monitors and maintains air pressure at a constant and proper level.

When it comes time to acquire new equipment, consideration should be given to aerodynamics, he said. Just about all of the Class 6, 7, and 8 vehicle producers offer fuel-efficient trucks and tractors with a complete aerodynamic package. Trailer manufacturers also offer various aerodynamic components and packages.

A more immediate action is to reduce maximum speeds, as higher speeds have been well documented as a major contributor to bad fuel economy, noted Cohn. Many fleets are lowering their governed speeds to 62 to 63 mph. While this is good for increasing fuel economy, it may lengthen trip time.


Road surfaces also affect fuel economy, he said. The smoother the road surface, the better the fuel economy.

Rough road surfaces may be good for traction, but very poor if your goal is to maximize fuel economy, he said. Additionally tires can wear out more rapidly due to the abrasive nature of some road surfaces.

The specific service routine or duty cycle of a fleet will also affect fuel economy. Pure line-haul service would get the best fuel economy versus poorer fuel economy for regional, local service, or severe-duty vocational fleet operation that involve a high degree of vehicle turning, stopping and starting, and poor surface conditions.

Drivers also have a major impact on fuel consumption, Cohn added. The driver that doesn't rapidly accelerate, is easy on turns, shifts gears at the appropriate time, and knows how to brake effectively gets the best fuel economy.

In addition to mentor programs, fuel bonuses, and other programs to encourage drivers to pay more attention to fuel economy, he observed that fleets are adopting automated manual transmissions to offset the impact new, inexperienced drivers have on fuel consumption.


Tires have a major impact on fuel economy, on top of their own escalating cost that is affected by oil prices, pointed out Cohn.

Next to the cost of fuel, tires are the highest expense for most fleets, he said. As the price of a barrel of oil increases (now at more than $125), the cost of diesel goes up, and so do tire prices. The reason being: almost all of the raw materials that are required to compound and build a commercial truck tire are oil based.

Tires also affect fuel economy when they are run at improper inflation pressures, especially when underinflated. An improperly inflated tire doesn't roll as smoothly or as easily as it was designed to, causing added rolling resistance, which increases fuel consumption.

Understanding the factors that affect fuel economy will help fleets choose the right strategy to maximize fuel economy and maximize profits, Cohn concluded. Fleets report that if they can increase their miles per gallon by even 1/10th (6.6 versus 6.5 miles per gallon), the savings is about $85,000 per year for a line-haul fleet of 100 vehicles, each traveling 120,000 miles per year.

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