Slight over-specing of engines improves fuel economy: Study

FORT LAUDERDALE, Fla. — Increasing torque ratings, lowering gear ratios, and making chassis improvements are just a few technical ways to maximize fuel efficiency, according to a new study by Florida-based PHH FirstFleet.

The 18-month, telematics-based fuel report of U.S. truck fleets in the grocery, manufacturing, fuel, and retail markets, is said to go beyond the study of speed monitoring and anti-idling as fuel-saving techniques.

Headed by applications engineer Ezel Baltali, the study concluded that by slightly over-spec’ing engines in order to run more consistently in the “sweet spot,” choosing a gear ratio low enough to suit a fleet’s application and location, and enabling the correct fuel-efficient, engine-specific parameters, fuel economy will improve by about 5 percent.

Higher gear ratios may improve performance and add power in
lower gears, additional power causes equipment to lose fuel economy.

When combined with other variables including progressive shifting, APUs and chassis improvements, the so-called “sweet spot” is where both fuel efficiency and performance are maximized.

In general, says the study, “fleet managers must choose the correct rear axle gear ratio for the fleet’s application and needs, but also consider that while higher gear ratios may improve overall performance and provide added power in lower gears, additional power causes equipment to lose fuel economy.”

Furthermore, speeding above 70 mph, demands over 60 percent of the engine’s total available horsepower, which significantly increases fuel consumption. “If speed is decreased to 55 mph in the appropriate gear, the horsepower demand is reduced to only 40 percent and draws less fuel.” Also, progressive shifting — drivers shifting quickly in lower gears prevents over-revving — decreases fuel consumption and increases fuel economy.

As for chassis improvements, new innovations in trailer aerodynamics, as well as roof fairings, side fairings, and bumper and side skirts, provide decreased wind resistance, which reduces required horsepower and thus fuel consumption.

Fleets should also consider low profile radial or wide based single tires, the study recommends. Fuel economy is said to improve as much as 5 percent because of decreased weight and lower rolling resistance.

In the future, PHH FirstFleet’s Fuel Study is expected to explore the relationship between maintenance, cost-per-mile and fuel efficiency.

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