Unlike light-duty pickup trucks and vans, which offer only a handful of options that can impact fuel economy, medium-duty trucks present dozens of choices that could either improve or diminish fuel efficiency. And, even a small variation in fuel consumption can make a big difference to a fleet’s bottom line when spread across hundreds or thousands of vehicles.

What should fleet managers consider when spec’ing medium-duty trucks to achieve optimal fuel efficiency and overall performance? Focus on these six areas:

1. Rightsizing the Chassis

First, determine how much of a load the truck will need to haul. 

“Just because the customer has been in a Class 7 truck in the past, we like to get a look at what the actual loads are. Get on the scale to find out what the true payload needs are and validate that the truck is matched to the payload needs,” said Mark Stumne, truck application engineer for GE Capital Fleet Services. “A lot of customers are trying to reduce truck size, moving down from a Class 7 to a Class 6, or from a Class 6 to a Class 5 truck. Yet, you need to balance fuel economy with maintenance cost considerations and ensure the truck is still able to do the job.”

2.Spec’ing the Engine

In Class 4 through Class 5 trucks, conventional engine options are limited. Usually, there is one diesel engine and, with some truck manufacturers, a gasoline option. But, with Class 6 and larger, there could be up to a dozen or more diesel engine horsepower and torque combinations to consider.

What option is best from a fuel-economy perspective? “This is best determined by understanding how fast a truck needs to go on the open road,” said Dan Shepherd, truck spec analyst for ARI, a full-service fleet management firm headquartered in Mt. Laurel, N.J.

According to Shepherd, “In a Class 6-7 truck, horsepower is a secondary function to torque rating. This rating dictates whether or not the truck will be able to start from a stopped position on a hill or flat surface, as well as being able to go up a certain grade of hill, while under load. In those situations, fuel economy becomes a lower priority because the truck is useless if it can’t move.”

A fleet manager can be selective when it comes to horsepower, because with certain OEMs, there may be two different engines with the same torque rating but different horsepower.

3. Reviewing Transmission Options

There are many more transmission options today then there were five years ago.

“The automatic transmissions now have six gears available, which allows us to talk about use of rear-end ratios that give us the startability (the torque required to move the truck from a complete stop, regardless of incline or load) we need, while being able to run the engine closer to its sweet spot,” Stumne said. “The extra gears in automatic transmissions and the new automated manual transmissions that have come out in recent years give us more options to consider, especially if you’re looking to downsize the truck for fuel efficiency and still get sufficient startability.”

What about manual transmissions?

“With manual transmissions, fuel efficiency really boils down to the driver,” said Jim Palin, truck application engineer for GE Capital Fleet Services. “Most fleets have decided that there are so few younger people coming into the driver world who know how to shift the manual transmission properly that the solution is to put them into a truck with an automatic transmission.”

4. Reviewing Drive-Axle Ratio Options

The drive-axle ratio option has a huge impact on fuel economy.

Too much gear uses a lot of fuel, but too little gear just won’t get the job done,” Shepherd said. “In the end, the axle ratio ultimately dictates the fuel efficiency in any spec.”

In medium-duty trucks, gear ratios range from as low as 2.69:1 to as high as 7.17:1, depending on the truck class, make and model, and rear-axle capacity.

How do fleet managers determine which drive-axle ratio is best for optimal fuel economy and performance for the job? Use the following guidelines:

• High numerical ratios. This is for maximum towing and payloads and on hilly terrain with steep grades.

• Mid-range numerical ratios. Spec this ratio when the truck requires flexibility for operating on varied terrain with moderate towing and payloads.

• Low numerical ratios. This makes sense for flat terrain, lighter loads, and running at consistent highway speeds.

5. Selecting the Right Tire

Having the right type of tire for the right road surface is very important.

“Tires must be able to handle the truck’s load in any application, but choosing a more aggressive tire when it might not be needed will create more friction on open road asphalt and that can lead to lower fuel economy,” according to Shepherd of ARI. “Much like drive axles, tires are a crucial component to fuel economy and performance and therefore must be chosen carefully.”

6. Making Upfit Considerations

How do upfit specifications — whether for truck bodies, cargo management systems, liftgates, or other equipment — affect medium-duty fuel economy?

“The material used as part of any upfit can have an impact on the overall performance of the truck,” Shepherd said. “For example, using [lightweight] aluminum or fiberglass will have a significantly different impact than steel in terms of fuel economy, if used in suitable applications. Also, fleet managers should make sure that any added components — such as a crane — are not over spec’ed for the truck. Adding unnecessary components results in unnecessary weight, which diminishes fuel efficiency.”

Palin with GE recommended that fleet managers also consider aerodynamic upfits, such as wind fairings installed above the cab on van body trucks, particularly in over-the-road delivery applications, to help achieve fuel savings when operating the truck at highway speeds.

The Bottom Line

Achieving fuel economy gains could be as simple as taking the time to refresh a truck’s spec.

“Sometimes fleet managers make decisions based on older models in their fleet, not knowing that newer, smaller vehicles are capable of doing the same job as the older ones, but can do it more efficiently,” Shepherd said. “It’s best to consider all of the options currently available in light of what you need, and then go from there.”